A morphological basis for path-dependent evolution of visual systems

Path dependence influences macroevolutionary predictability by constraining potential outcomes after critical evolutionary junctions. Although it has been demonstrated in laboratory experiments, path dependence is difficult to demonstrate in natural systems because of a lack of independent replicates. Here, we show that two types of distributed visual systems recently evolved twice within chitons, demonstrating rapid and path-dependent evolution of a complex trait. The type of visual system that a chiton lineage can evolve is constrained by the number of openings for sensory nerves in its shell plates. Lineages with more openings evolve visual systems with thousands of eyespots, whereas those with fewer openings evolve visual systems with hundreds of shell eyes. These macroevolutionary outcomes shaped by path dependence are both deterministic and stochastic because possibilities are restricted yet not entirely predictable.

Distribution of Axial Length in Australians of Different Age Groups, Ethnicities, and Refractive Errors

Purpose

Treatments are available to slow myopic axial elongation. Understanding normal axial length (AL) distributions will assist clinicians in choosing appropriate treatment for myopia. We report the distribution of AL in Australians of different age groups and refractive errors.

Methods

Retrospectively collected spherical equivalent refraction (SER) and AL data of 5938 individuals aged 5 to 89 years from 8 Australian studies were included. Based on the SER, participants were classified as emmetropes, myopes, and hyperopes. Two regression model parameterizations (piece-wise and restricted cubic splines [RCS]) were applied to the cross-sectional data to analyze the association between age and AL. These results were compared with longitudinal data from the Raine Study where the AL was measured at age 20 (baseline) and 28 years.

Results

A piece-wise regression model (with 1 knot) showed that myopes had a greater increase in AL before 18 years by 0.119 mm/year (P < 0.001) and after 18 years by 0.011 mm/year (P < 0.001) compared to emmetropes and hyperopes, with the RCS model (with 3 knots) showing similar results. The longitudinal data from the Raine Study revealed that, when compared to emmetropes, only myopes showed a significant change in the AL in young adulthood (by 0.016 mm/year, P < 0.001).

Conclusions

The AL of myopic eyes increases more rapidly in childhood and slightly in early adulthood. Further studies of longitudinal changes in AL, particularly in childhood, are required to guide myopia interventions.

Translational Relevance

The axial length of myopic eyes increases rapidly in childhood, and there is a minimal increase in the axial length in non-myopic eyes after 18 years of age.

Alteration of organ size and allometric scaling by organ-specific targeting of IGF signaling

The size of an organ is proportional to the other body parts or the whole body. This relationship is known as allometry. Understanding how allometry is determined is a fundamental question in biology. Here we tested the hypothesis that local insulin-like growth factor (Igf) signaling is critical in regulating organ size and its allometric scaling by organ-specific expression of Igf binding protein (Igfbp). Overexpression of Igfbp2a or 5b in the developing zebrafish eye, heart, and inner ear resulted in a disproportional reduction in their growth relative to the body. Stable transgenic zebrafish with lens-specific Igfbp5b expression selectively reduced adult eye size. The action is Igf-dependent because an Igf-binding deficient Igfbp5b mutant had no effect. Targeted expression of a dominant-negative Igf1 receptor (dnIgf1r) in the lens caused a similar reduction in relative eye growth. Furthermore, co-expression of IGF-1 with an Igfbp restored the eye size. Finally, co-expression of a constitutively active form of Akt with Igfbp or dnIgf1r restored the relative eye growth. These data suggest that local Igf availability and Igf signaling activity are critical determinants of organ size and allometric scaling in zebrafish.

Eye morphogenesis in the blind Mexican cavefish

The morphogenesis of the vertebrate eye consists of a complex choreography of cell movements, tightly coupled to axial regionalization and cell type specification processes. Disturbances in these events can lead to developmental defects and blindness. Here, we have deciphered the sequence of defective events leading to coloboma in the embryonic eye of the blind cavefish of the species Astyanax mexicanus. Using comparative live imaging on targeted enhancer-trap Zic1:hsp70:GFP reporter lines of both the normal, river-dwelling morph and the cave morph of the species, we identified defects in migratory cell behaviours during evagination that participate in the reduced optic vesicle size in cavefish, without proliferation defect. Further, impaired optic cup invagination shifts the relative position of the lens and contributes to coloboma in cavefish. Based on these results, we propose a developmental scenario to explain the cavefish phenotype and discuss developmental constraints to morphological evolution. The cavefish eye appears as an outstanding natural mutant model to study molecular and cellular processes involved in optic region morphogenesis.

Elastic Instabilities Govern the Morphogenesis of the Optic Cup

Because the normal operation of the eye depends on sensitive morphogenetic processes for its eventual shape, developmental flaws can lead to wide-ranging ocular defects. However, the physical processes and mechanisms governing ocular morphogenesis are not well understood. Here, using analytical theory and nonlinear shell finite-element simulations, we show, for optic vesicles experiencing matrix-constrained growth, that elastic instabilities govern the optic cup morphogenesis. By capturing the stress amplification owing to mass increase during growth, we show that the morphogenesis is driven by two elastic instabilities analogous to the snap through in spherical shells, where the second instability is sensitive to the optic cup geometry. In particular, if the optic vesicle is too slender, it will buckle and break axisymmetry, thus, preventing normal development. Our results shed light on the morphogenetic mechanisms governing the formation of a functional biological system and the role of elastic instabilities in the shape selection of soft biological structures.

Early Pediatric Benefit of Lutein for Maturing Eyes and Brain-An Overview

Lutein is a dietary carotenoid preferentially accumulated in the eye and the brain in early life and throughout the life span. Lutein accumulation in areas of high metabolism and oxidative stress such as the eye and the brain suggest a unique role of this ingredient during the development and maturation of these organs of common embryological origin. Lutein is naturally provided to the developing baby via the cord blood, breast milk and then infant diet. The presence of this carotenoid depends on fruit and vegetable intakes and its bioavailability is higher in breastmilk. This paper aims to review the anatomical development of the eye and the brain, explore the presence and selective deposition of lutein in these organs during pregnancy and infancy and, based on its functional characteristics, present the latest available research on the beneficial role of lutein in the pediatric population. The potential effects of lutein in ameliorating conditions associated with increase oxidative stress such as in prematurity will be also addressed. Since consumption of lutein rich foods falls short of government guidelines and in most region of the world infant formulas lack this bioactive, dietary recommendations for pregnant and breastfeeding women and their child can help to bridge the gap.

Crumbs and the apical spectrin cytoskeleton regulate R8 cell fate in the Drosophila eye

The Hippo pathway is an important regulator of organ growth and cell fate. In the R8 photoreceptor cells of the Drosophila melanogaster eye, the Hippo pathway controls the fate choice between one of two subtypes that express either the blue light-sensitive Rhodopsin 5 (Hippo inactive R8 subtype) or the green light-sensitive Rhodopsin 6 (Hippo active R8 subtype). The degree to which the mechanism of Hippo signal transduction and the proteins that mediate it are conserved in organ growth and R8 cell fate choice is currently unclear. Here, we identify Crumbs and the apical spectrin cytoskeleton as regulators of R8 cell fate. By contrast, other proteins that influence Hippo-dependent organ growth, such as the basolateral spectrin cytoskeleton and Ajuba, are dispensable for the R8 cell fate choice. Surprisingly, Crumbs promotes the Rhodopsin 5 cell fate, which is driven by Yorkie, rather than the Rhodopsin 6 cell fate, which is driven by Warts and the Hippo pathway, which contrasts with its impact on Hippo activity in organ growth. Furthermore, neither the apical spectrin cytoskeleton nor Crumbs appear to regulate the Hippo pathway through mechanisms that have been observed in growing organs. Together, these results show that only a subset of Hippo pathway proteins regulate the R8 binary cell fate decision and that aspects of Hippo signalling differ between growing organs and post-mitotic R8 cells.

Emmetropisation responses when visual information is presented at only one or two near target planes in chick*

PURPOSE

When visual information is confined to one object plane and zero or hyperopic defocus is present, emmetropisation is directed towards this plane, when myopic defocus is present, emmetropisation processes fail. We investigated the effect of introducing information at a second nearer plane on emmetropisation responses under these conditions.

METHODS

The visual environment was controlled using lenses (+30 D, +40 D and +50 D) and cones with a Maltese cross target (MX) at one or two distances. Four different target configurations were used: 1. a single target was located at 3.3 cm, 2. a vertical hemi-field target was added at 2.5 cm, 3. a transparent target was added at 2.5 cm or 4. a single target was located at 2.5 cm. An additional cone length of 4.0 cm and nearer target distance of 3.3 cm was used with the +50 D lens. The imaging devices were applied monocularly to eight-day-old chicks and worn for four days. At the end of the treatment, refractive errors and eye growth were measured. Potential regional differences in growth were also assessed.

RESULTS

The configuration of the target and the interaction between target configuration and lens power had significant refractive and axial growth effects. With a single target plane, myopic and hyperopic defocus resulted in myopia. When defocus was experienced at two planes, refractive errors shifted towards the plane with the lower defocus and emmetropisation responses, although still not normal, were more consistent.

CONCLUSIONS

When visual information is provided at two distances, the target with the lesser incident defocus has the greater influence on the resultant refractive error. Emmetropisation responses are more accurate when information is presented at many distances.

The biological basis of myopic refractive error

Myopia is among the most common refractive errors and is associated with the greatest risk of pathological outcomes. Most animals, including humans, are born with hyperopic errors. During development, axial elongation of the eye occurs and is regulated through a vision-dependent process, known as emmetropisation The extremely rapid changes in the prevalence of myopia and the dependence of myopia on the level of education indicate that there are very strong environmental impacts on the development of myopia. This conflicts with the common occurrence of familial patterns of inheritance of myopia, which suggests a role for genetic determination. There are more than 150 defined genetic syndromes in which familial high myopia is one of the features, including some that are not associated with other syndromes. The evidence for the roles of both nature and nurture in the aetiology of myopia is discussed. This review also examines the experimentally induced refractive errors associated with form-deprivation, recovery from form deprivation and the effects of both negative and positive lenses. In addition, it looks at the local and optical control of eye growth. Finally, the various control pathways for growth are considered. These include dopamine, ZENK-glucagon, retinoic acid and retinoic acid receptors, crystallin, seratonin and melatonin, vasoactive intestinal peptide and enkephalins, nitric oxide and various growth factors.

Light-induced and circadian expressions of melanopsin genes opn4xa and opn4xb in the eyes of juvenile grass puffer Takifugu alboplumbeus

Animals regulate a variety of aspects of physiology according to environmental light conditions via nonvisual opsins such as melanopsin. In order to study photic regulation of fish physiology, expression changes of the genes for melanopsin (opn4xa and opn4xb) and effects of light on them were examined in juvenile grass puffer Takifugu alboplumbeus using quantitative real-time PCR. In the brain of juvenile fish, no significant diurnal nor circadian changes were observed in opn4x mRNA levels. On the other hand, in the eyes, the mRNA level of opn4xa showed a significant diurnal rhythm with a peak at Zeitgeber time (ZT) 4, while no apparent circadian changes were observed. The mRNA level of opn4xb in the eyes showed a diurnal change similar to that of opn4xa, while it showed a significant circadian change. Furthermore, continuous exposure to light during a subjective night significantly increased the mRNA levels of opn4xa in the eyes at ZT24, suggesting that light induces gene expression of opn4xa in the eyes and that the induction occurs only during the night-day transition period. These results suggest that Opn4xa and Opn4xb play differential roles in the eyes of juvenile grass puffer to mediate the physiological effects of environmental light information.

Identification of MFRP and the secreted serine proteases PRSS56 and ADAMTS19 as part of a molecular network involved in ocular growth regulation

Precise regulation of ocular size is a critical determinant of normal visual acuity. Although it is generally accepted that ocular growth relies on a cascade of signaling events transmitted from the retina to the sclera, the factors and mechanism(s) involved are poorly understood. Recent studies have highlighted the importance of the retinal secreted serine protease PRSS56 and transmembrane glycoprotein MFRP, a factor predominantly expressed in the retinal pigment epithelium (RPE), in ocular size determination. Mutations in PRSS56 and MFRP constitute a major cause of nanophthalmos, a condition characterized by severe reduction in ocular axial length/extreme hyperopia. Interestingly, common variants of these genes have been implicated in myopia, a condition associated with ocular elongation. Consistent with these findings, mice with loss of function mutation in PRSS56 or MFRP exhibit a reduction in ocular axial length. However, the molecular network and cellular processes involved in PRSS56- and MFRP-mediated ocular axial growth remain elusive. Here, we show that Adamts19 expression is significantly upregulated in the retina of mice lacking either Prss56 or Mfrp. Importantly, using genetic mouse models, we demonstrate that while ADAMTS19 is not required for ocular growth during normal development, its inactivation exacerbates ocular axial length reduction in Prss56 and Mfrp mutant mice. These results suggest that the upregulation of retinal Adamts19 is part of an adaptive molecular response to counteract impaired ocular growth. Using a complementary genetic approach, we show that loss of PRSS56 or MFRP function prevents excessive ocular axial growth in a mouse model of early-onset myopia caused by a null mutation in Irbp, thus, demonstrating that PRSS56 and MFRP are also required for pathological ocular elongation. Collectively, our findings provide new insights into the molecular network involved in ocular axial growth and support a role for molecular crosstalk between the retina and RPE involved in refractive development.

During ocular refractive development, the eye’s growth is modulated, such that the ocular axial length matches the optical power enabling the eyes to achieve optimal focus. Alterations in ocular growth mainly contribute to refractive errors. Mutations in human PRSS56 and MFRP are responsible for nanophthalmos that exhibit a severe reduction in ocular axial length, and high hyperopia. Importantly, mutant mouse models lacking either Müller glia expressed PRSS56, or retinal pigment epithelium (RPE) localized MFRP exhibit ocular axial length reduction. Here, we have identified Adamts19 as a factor whose levels were significantly upregulated in the retina of mice lacking either Prss56 or Mfrp. Importantly, utilizing Adamts19 knockout mice we demonstrate that upregulation of retinal Adamts19 expression constitutes a compensatory mechanism that provides partial protection against ocular axial reduction due to mutation in Prss56 and Mfrp. Next, utilizing a mouse model of early-onset myopia, we demonstrate that the mutant Irbp induced ocular axial elongation is completely dependent on Prss56 as well as Mfrp, suggesting an interplay between Müller glia and RPE in the regulation of ocular axial growth. Collectively, these findings suggest that ocular refractive development relies on complex interactions occurring between genetic factors in the retina and RPE.

E3 ubiquitin ligase-mediated regulation of vertebrate ocular development; new insights into the function of SIAH enzymes

Developmental regulation of the vertebrate visual system has been a focus of investigation for generations as understanding this critical time period has direct implications on our understanding of congenital blinding disease. The majority of studies to date have focused on transcriptional regulation mediated by morphogen gradients and signaling pathways. However, recent studies of post translational regulation during ocular development have shed light on the role of the ubiquitin proteasome system (UPS). This rather ubiquitous yet highly diverse system is well known for regulating protein function and localization as well as stability via targeting for degradation by the 26S proteasome. Work from many model organisms has recently identified UPS activity during various milestones of ocular development including retinal morphogenesis, retinal ganglion cell function as well as photoreceptor homeostasis. In particular work from flies and zebrafish has highlighted the role of the E3 ligase enzyme family, Seven in Absentia Homologue (Siah) during these events. In this review, we summarize the current understanding of UPS activity during Drosophila and vertebrate ocular development, with a major focus on recent findings correlating Siah E3 ligase activity with two major developmental stages of vertebrate ocular development, retinal morphogenesis and photoreceptor specification and survival.

Hmx1 regulates urfh1 expression in the craniofacial region in zebrafish

H6 family homeobox 1 (HMX1) regulates multiple aspects of craniofacial development as it is widely expressed in the eye, peripheral ganglia and branchial arches. Mutations in HMX1 are linked to an ocular defect termed Oculo-auricular syndrome of Schorderet-Munier-Franceschetti (MIM #612109). We identified UHRF1 as a target of HMX1 during development. UHRF1 and its partner proteins actively regulate chromatin modifications and cellular proliferation. Luciferase assays and in situ hybridization analyses showed that HMX1 exerts a transcriptional inhibitory effect on UHRF1 and a modification of its expression pattern. Overexpression of hmx1 in hsp70-hmx1 zebrafish increased uhrf1 expression in the cranial region, while mutations in the hmx1 dimerization domains reduced uhrf1 expression. Moreover, the expression level of uhrf1 and its partner dnmt1 was increased in the eye field in response to hmx1 overexpression. These results indicate that hmx1 regulates uhrf1 expression and, potentially through regulating the expression of factors involved in DNA methylation, contribute to the development of the craniofacial region of zebrafish.

The Pax6 master control gene initiates spontaneous retinal development via a self-organising Turing network

Understanding how complex organ systems are assembled from simple embryonic tissues is a major challenge. Across the animal kingdom a great diversity of visual organs are initiated by a 'master control gene' called Pax6, which is both necessary and sufficient for eye development. Yet precisely how Pax6 achieves this deeply homologous function is poorly understood. Using the chick as a model organism, we show that vertebrate Pax6 interacts with a pair of morphogen-coding genes, Tgfb2 and Fst, to form a putative Turing network, which we have computationally modelled. Computer simulations suggest that this gene network is sufficient to spontaneously polarise the developing retina, establishing the first organisational axis of the eye and prefiguring its further development. Our findings reveal how retinal self-organisation may be initiated independently of the highly ordered tissue interactions that help to assemble the eye in vivo These results help to explain how stem cell aggregates spontaneously self-organise into functional eye-cups in vitro We anticipate these findings will help to underpin retinal organoid technology, which holds much promise as a platform for disease modelling, drug development and regenerative therapies.

Defining the relationship between maternal care behavior and sensory development in Wistar rats: Auditory periphery development, eye opening and brain gene expression

Defining the relationship between maternal care, sensory development and brain gene expression in neonates is important to understand the impact of environmental challenges during sensitive periods in early life. In this study, we used a selection approach to test the hypothesis that variation in maternal licking and grooming (LG) during the first week of life influences sensory development in Wistar rat pups. We tracked the onset of the auditory brainstem response (ABR), the timing of eye opening (EO), middle ear development with micro-CT X-ray tomography, and used qRT-PCR to monitor changes in gene expression of the hypoxia-sensitive pathway and neurotrophin signaling in pups reared by low-LG or high-LG dams. The results show the first evidence that the transcription of genes involved in the hypoxia-sensitive pathway and neurotrophin signaling is regulated during separate sensitive periods that occur before and after hearing onset, respectively. Although the timing of ABR onset, EO, and the relative mRNA levels of genes involved in the hypoxia-sensitive pathway did not differ between pups from different LG groups, we found statistically significant increases in the relative mRNA levels of four genes involved in neurotrophin signaling in auditory brain regions from pups of different LG backgrounds. These results suggest that sensitivity to hypoxic challenge might be widespread in the auditory system of neonate rats before hearing onset, and that maternal LG may affect the transcription of genes involved in experience-dependent neuroplasticity.

Effect of Age at Primary Intraocular Lens Implantation on Refractive Growth in Young Children

PURPOSE

To evaluate the effect of age at primary intraocular lens (IOL) implantation on rate of refractive growth (RRG3) during childhood.

METHODS

A retrospective chart review was performed for children undergoing primary IOL implantation during cataract surgery. RRG3 was calculated for one eye from each patient using the first postoperative refraction, last refraction that remained stable (< 1.00 diopters [D] change/2 years), and the corresponding ages. RRG3 values for pseudophakic patients operated on from ages 0 to 5 months were compared with values for patients operated on at ages 6 to 23 months and 24 to 72 months. Patients with refractive errors that stabilized were grouped by age at surgery to compare age at refractive plateau.

RESULTS

Of 296 eyes identified from 219 patients, 46 eyes met the inclusion criteria. There was a statistically significant difference in RRG3 among age groups. The mean RRG3 value was -19.82 ± 5.23 D for the 0 to 5 months group, -22.32 ± 7.45 D for the 6 to 23 months group (0 to 5 months vs 6 to 23 months, P = .43), and -9.64 ± 11.95 D for the 24 to 72 months group (0 to 5 months vs 24 to 72 months, P = .01).

CONCLUSIONS

Age at primary IOL implantation affects the RRG3, especially for children 0 to 23 months old at surgery. Surgeons performing primary IOL implantation in infants may want to use age-adjusted assumptions, because faster refractive growth rates can be expected in young children. [J Pediatr Ophthalmol Strabismus. 2020;57(4):264-270.].

Intimate functional interactions between TGS1 and the Smn complex revealed by an analysis of the Drosophila eye development

Trimethylguanosine synthase 1 (TGS1) is a conserved enzyme that mediates formation of the trimethylguanosine cap on several RNAs, including snRNAs and telomerase RNA. Previous studies have shown that TGS1 binds the Survival Motor Neuron (SMN) protein, whose deficiency causes spinal muscular atrophy (SMA). Here, we analyzed the roles of the Drosophila orthologs of the human TGS1 and SMN genes. We show that the Drosophila TGS1 protein (dTgs1) physically interacts with all subunits of the Drosophila Smn complex (Smn, Gem2, Gem3, Gem4 and Gem5), and that a human TGS1 transgene rescues the mutant phenotype caused by dTgs1 loss. We demonstrate that both dTgs1 and Smn are required for viability of retinal progenitor cells and that downregulation of these genes leads to a reduced eye size. Importantly, overexpression of dTgs1 partially rescues the eye defects caused by Smn depletion, and vice versa. These results suggest that the Drosophila eye model can be exploited for screens aimed at the identification of genes and drugs that modify the phenotypes elicited by Tgs1 and Smn deficiency. These modifiers could help to understand the molecular mechanisms underlying SMA pathogenesis and devise new therapies for this genetic disease.

We explored the functional relationships between TGS1 and SMN using Drosophila as model organism. TGS1 is an enzyme that modifies the structure of the 5’-end of several RNAs, including telomerase RNA and the small nuclear RNAs (snRNAs) that are required for messenger RNA maturation. The SMN protein regulates snRNAs biogenesis and mutations in human SMN cause Spinal Muscular Atrophy (SMA), a devastating disorder characterized by neurodegeneration, progressive paralysis and death. We show that mutations in the Drosophila TGS1 (dTgs1) gene cause lethality, which is rescued by a human TGS1 transgene. We also show that the dTgs1 protein physically interacts with all subunits of the Smn complex, and that downregulation of either dTgs1 or Smn leads to a reduced Drosophila eye size. Notably, overexpression of dTgs1 partially rescues the eye defects caused by Smn knockdown, and vice versa, indicating that these genes cooperate in eye development. These results suggest that the eye model can be exploited for screens aimed at detection of chemical and genetic modifiers of the eye mutant phenotype elicited by dTgs1 and Smn deficiency, providing new clues about SMA pathogenesis and potential therapies.

Identification of genomic enhancers through spatial integration of single-cell transcriptomics and epigenomics

Single-cell technologies allow measuring chromatin accessibility and gene expression in each cell, but jointly utilizing both layers to map bona fide gene regulatory networks and enhancers remains challenging. Here, we generate independent single-cell RNA-seq and single-cell ATAC-seq atlases of the Drosophila eye-antennal disc and spatially integrate the data into a virtual latent space that mimics the organization of the 2D tissue using ScoMAP (Single-Cell Omics Mapping into spatial Axes using Pseudotime ordering). To validate spatially predicted enhancers, we use a large collection of enhancer-reporter lines and identify ~ 85% of enhancers in which chromatin accessibility and enhancer activity are coupled. Next, we infer enhancer-to-gene relationships in the virtual space, finding that genes are mostly regulated by multiple, often redundant, enhancers. Exploiting cell type-specific enhancers, we deconvolute cell type-specific effects of bulk-derived chromatin accessibility QTLs. Finally, we discover that Prospero drives neuronal differentiation through the binding of a GGG motif. In summary, we provide a comprehensive spatial characterization of gene regulation in a 2D tissue.

Zika virus non-structural protein NS4A restricts eye growth in Drosophila through regulation of JAK/STAT signaling

To gain a comprehensive view of the changes in host gene expression underlying Zika virus (ZIKV) pathogenesis, we performed whole-genome RNA sequencing (RNA-seq) of ZIKV-infected Drosophila adult flies. RNA-seq analysis revealed that ZIKV infection alters several and diverse biological processes, including stress, locomotion, lipid metabolism, imaginal disc morphogenesis and regulation of JAK/STAT signaling. To explore the interaction between ZIKV infection and JAK/STAT signaling regulation, we generated genetic constructs overexpressing ZIKV-specific non-structural proteins NS2A, NS2B, NS4A and NS4B. We found that ectopic expression of non-structural proteins in the developing Drosophila eye significantly restricts growth of the larval and adult eye and correlates with considerable repression of the in vivo JAK/STAT reporter, 10XStat92E-GFP At the cellular level, eye growth defects are associated with reduced rate of proliferation without affecting the overall rate of apoptosis. In addition, ZIKV NS4A genetically interacts with the JAK/STAT signaling components; co-expression of NS4A along with the dominant-negative form of domeless or StatRNAi results in aggravated reduction in eye size, while co-expression of NS4A in HopTuml (also known as hopTum ) mutant background partially rescues the hop-induced eye overgrowth phenotype. The function of ZIKV NS4A in regulating growth is maintained in the wing, where ZIKV NS4A overexpression in the pouch domain results in reduced growth linked with diminished expression of Notch targets, Wingless (Wg) and Cut, and the Notch reporter, NRE-GFP Thus, our study provides evidence that ZIKV infection in Drosophila results in restricted growth of the developing eye and wing, wherein eye phenotype is induced through regulation of JAK/STAT signaling, whereas restricted wing growth is induced through regulation of Notch signaling. The interaction of ZIKV non-structural proteins with the conserved host signaling pathways further advance our understanding of ZIKV-induced pathogenesis.This article has an associated First Person interview with the first author of the paper.

Medroxyprogesterone acetate affects eye growth and the transcription of associated genes in zebrafish

Medroxyprogesterone acetate (MPA) is a widely used synthetic progestin in contraception pills and hormone replacement therapy. However, its effects on eye growth and development and function were largely unknown. In this study, the transcription of genes in the Notch signaling pathway and the visual cycle network were evaluated after chronic MPA exposure at 4.32 (L), 42.0 (M), and 424 (H) ng L^-1 for 120 days in zebrafish. Meanwhile, the histology of the eyes was also examined. Transcriptional results showed that MPA at all three concentrations significantly increased the transcription of notch1a, dll4, jag1a, ctbp1 and rbpjb (key genes in the Notch signaling pathway) in the eyes of females. The up-regulation of noth1a, ctbp1 and kat2b was also observed in the eyes of males exposed to MPA at 424 ng L^-1. In the visual cycle pathway, MPA increased the transcription of opn1sw1, opn1sw2, arr3a and rpe65a in the eyes of females from the M and H treatments. Histopathological analysis showed that exposure to 42.0 ng L^-1 of MPA increased the thicknesses of inner nuclear layer in females and outer segment in males. Moreover, exposure to 424 ng L^-1 of MPA increased the lens diameter in females. These results indicated that chronic MPA exposure affected the transcription of genes in the Notch signaling and in the visual cycle pathways, resulting in overgrowth of the eyes and interference of the eye functions. This study suggests that MPA pose a risk to fitness and survival of zebrafish in areas where MPA contamination exists.

Distinct and Overlapping Expression Patterns of the Homer Family of Scaffolding Proteins and Their Encoding Genes in Developing Murine Cephalic Tissues

In mammals Homer1, Homer2 and Homer3 constitute a family of scaffolding proteins with key roles in Ca²⁺ signaling and Ca²⁺ transport. In rodents, Homer proteins and mRNAs have been shown to be expressed in various postnatal tissues and to be enriched in brain. However, whether the Homers are expressed in developing tissues is hitherto largely unknown. In this work, we used immunohistochemistry and in situ hybridization to analyze the expression patterns of Homer1, Homer2 and Homer3 in developing cephalic structures. Our study revealed that the three Homer proteins and their encoding genes are expressed in a wide range of developing tissues and organs, including the brain, tooth, eye, cochlea, salivary glands, olfactory and respiratory mucosae, bone and taste buds. We show that although overall the three Homers exhibit overlapping distribution patterns, the proteins localize at distinct subcellular domains in several cell types, that in both undifferentiated and differentiated cells Homer proteins are concentrated in puncta and that the vascular endothelium is enriched with Homer3 mRNA and protein. Our findings suggest that Homer proteins may have differential and overlapping functions and are expected to be of value for future research aiming at deciphering the roles of Homer proteins during embryonic development.

Effects of tritiated water on locomotion of zebrafish larvae: a new insight in tritium toxic effects on a vertebrate model species

Tritium (³H), a radioactive isotope of hydrogen, is ubiquitously present in the environment. In a previous study, we highlighted a mis-regulation of genes involved in muscle contraction, eye transparency and response to DNA damages after exposure of zebrafish embryo-larvae from 3 hpf to 96 hpf at 0.4 and 4 mGy/h of tritiated water (HTO). The present study aimed to link this gene mis-regulation to responses observed at higher biological levels. Analyses on spontaneous tail movement, locomotor activity and heart rate were performed. Histological sections of eyes were made to evaluate the impact of HTO on eye transparency and whole embryo immunostainings were realized to assess DNA double strand breaks repair using gamma-H2AX foci. We found a decrease of basal velocity as well as a decrease of response in 96 hpf larvae exposed at 0.4 mGy/h after a tactile stimulus as compared to controls. Histological sections of larvae eyes performed after the exposure to 4 mGy/h did not show obvious differences in lens transparency or retinal development between contaminated and control organisms. Gamma-H2AX foci detection revealed no differences in the number of foci between contaminated organisms and controls, for both dose rates. Overall, results highlighted more detrimental effects of HTO exposure on locomotor behavior in 96 hpf larvae exposed at the lowest dose rate. Those results could be linked to mis-regulation of genes involved in muscle contraction found in a previous study at the same dose rate. It appears that not all effects found at the molecular scale were confirmed using higher biological scales. These results could be due to a delay between gene expression modulation and the onset of physiological disruption or homeostatic mechanisms to deal with tritium effects. However, crossing data from different scales highlighted new pathways to explore, i.e. neurotoxic pathways, for better understanding HTO effects on organisms.

Biallelic Deletion of Pxdn in Mice Leads to Anophthalmia and Severe Eye Malformation

Peroxidasin (PXDN) is a unique peroxidase containing extracellular matrix motifs and stabilizes collagen IV networks by forming sulfilimine crosslinks. PXDN gene knockout in Caenorhabditis elegans (C. elegans) and Drosophila results in the demise at the embryonic and larval stages. PXDN mutations lead to severe eye disorders, including microphthalmia, cataract, glaucoma, and anterior segment dysgenesis in humans and mice. To investigate how PXDN loss of function affects organ development, we generated Pxdn knockout mice by deletion of exon 1 and its 5′ upstream sequences of the Pxdn gene using the CRISPR/Cas9 system. Loss of both PXDN expression and collagen IV sulfilimine cross-links was detected only in the homozygous mice, which showed completely or almost closed eyelids with small eyes, having no apparent external morphological defects in other organs. In histological analysis of eye tissues, the homozygous mice had extreme defects in eye development, including no eyeballs or drastically disorganized eye structures, whereas the heterozygous mice showed normal eye structure. Visual function tests also revealed no obvious functional abnormalities in the eyes between heterozygous mice and wild-type mice. Thus, these results suggest that PXDN activity is essential in eye development, and also indicate that a single allele of Pxdn gene is sufficient for eye-structure formation and normal visual function.

Drift and Directional Selection Are the Evolutionary Forces Driving Gene Expression Divergence in Eye and Brain Tissue of Heliconius Butterflies

Investigating gene expression evolution over micro- and macroevolutionary timescales will expand our understanding of the role of gene expression in adaptation and speciation. In this study, we characterized the evolutionary forces acting on gene expression levels in eye and brain tissue of five Heliconius butterflies with divergence times of ∼5-12 MYA. We developed and applied Brownian motion (BM) and Ornstein-Uhlenbeck (OU) models to identify genes whose expression levels are evolving through drift, stabilizing selection, or a lineage-specific shift. We found that 81% of the genes evolve under genetic drift. When testing for branch-specific shifts in gene expression, we detected 368 (16%) shift events. Genes showing a shift toward upregulation have significantly lower gene expression variance than those genes showing a shift leading toward downregulation. We hypothesize that directional selection is acting in shifts causing upregulation, since transcription is costly. We further uncovered through simulations that parameter estimation of OU models is biased when using small phylogenies and only becomes reliable with phylogenies having ≥ 50 taxa. Therefore, we developed a new statistical test based on BM to identify highly conserved genes (i.e., evolving under strong stabilizing selection), which comprised 3% of the orthoclusters. In conclusion, we found that drift is the dominant evolutionary force driving gene expression evolution in eye and brain tissue in Heliconius Nevertheless, the higher proportion of genes evolving under directional than under stabilizing selection might reflect species-specific selective pressures on vision and the brain that are necessary to fulfill species-specific requirements.

Predicting gene regulatory interactions based on spatial gene expression data and deep learning

Reverse engineering of gene regulatory networks (GRNs) is a central task in systems biology. Most of the existing methods for GRN inference rely on gene co-expression analysis or TF-target binding information, where the determination of co-expression is often unreliable merely based on gene expression levels, and the TF-target binding data from high-throughput experiments may be noisy, leading to a high ratio of false links and missed links, especially for large-scale networks. In recent years, the microscopy images recording spatial gene expression have become a new resource in GRN reconstruction, as the spatial and temporal expression patterns contain much abundant gene interaction information. Till now, the spatial expression resources have been largely underexploited, and only a few traditional image processing methods have been employed in the image-based GRN reconstruction. Moreover, co-expression analysis using conventional measurements based on image similarity may be inaccurate, because it is the local-pattern consistency rather than global-image-similarity that determines gene-gene interactions. Here we present GripDL (Gene regulatory interaction prediction via Deep Learning), which incorporates high-confidence TF-gene regulation knowledge from previous studies, and constructs GRNs for Drosophila eye development based on Drosophila embryonic gene expression images. Benefitting from the powerful representation ability of deep neural networks and the supervision information of known interactions, the new method outperforms traditional methods with a large margin and reveals new intriguing knowledge about Drosophila eye development.

Analysis of genetic networks regulating refractive eye development in collaborative cross progenitor strain mice reveals new genes and pathways underlying human myopia

BACKGROUND

Population studies suggest that genetic factors play an important role in refractive error development; however, the precise role of genetic background and the composition of the signaling pathways underlying refractive eye development remain poorly understood.

METHODS

Here, we analyzed normal refractive development and susceptibility to form-deprivation myopia in the eight progenitor mouse strains of the Collaborative Cross (CC). We used RNA-seq to analyze gene expression in the retinae of these mice and reconstruct genetic networks and signaling pathways underlying refractive eye development. We also utilized genome-wide gene-based association analysis to identify mouse genes and pathways associated with myopia in humans.

RESULTS

Genetic background strongly influenced both baseline refractive development and susceptibility to environmentally-induced myopia. Baseline refractive errors ranged from - 21.2 diopters (D) in 129S1/svlmj mice to + 22.0 D in CAST/EiJ mice and represented a continuous distribution typical of a quantitative genetic trait. The extent of induced form-deprivation myopia ranged from - 5.6 D in NZO/HILtJ mice to - 20.0 D in CAST/EiJ mice and also followed a continuous distribution. Whole-genome (RNA-seq) gene expression profiling in retinae from CC progenitor strains identified genes whose expression level correlated with either baseline refractive error or susceptibility to myopia. Expression levels of 2,302 genes correlated with the baseline refractive state of the eye, whereas 1,917 genes correlated with susceptibility to induced myopia. Genome-wide gene-based association analysis in the CREAM and UK Biobank human cohorts revealed that 985 of the above genes were associated with myopia in humans, including 847 genes which were implicated in the development of human myopia for the first time. Although the gene sets controlling baseline refractive development and those regulating susceptibility to myopia overlapped, these two processes appeared to be controlled by largely distinct sets of genes.

CONCLUSIONS

Comparison with data for other animal models of myopia revealed that the genes identified in this study comprise a well-defined set of retinal signaling pathways, which are highly conserved across different vertebrate species. These results identify major signaling pathways involved in refractive eye development and provide attractive targets for the development of anti-myopia drugs.

Peptidomic analysis of zebrafish embryos exposed to polychlorinated biphenyls and their impact on eye development

Polychlorinated biphenyls (PCBs), a class of persistent organic pollutant, are closely related to abnormal eye development in children. However, little is known regarding the role of peptides in the development of PCB-induced ocular dysplasia. To characterize the nature of PCB exposure on peptides involved in the development of the ocular system, we used liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) to detect differential expression of peptides between normal and PCB-exposed zebrafish embryos. A total of 7900 peptides were analyzed, 90 of which were differentially expressed, with 29 being up-regulated and 61 down-regulated. These peptides were investigated using ingenuity pathway analysis (IPA) and gene ontology (GO) analysis to explore their role in eye development. This study identified 18 peptides associated with the development of the optic nerve and ocular system in the PCB-exposure group, as well as 10 peptides that are located in the functional domain of their precursor proteins. These peptides provide potential biomarkers for the treatment of ocular dysplasia caused by PCBs and may help us understand the mechanism of abnormal eye development caused by organic pollutants.

Multilevel regulation of the glass locus during Drosophila eye development

Development of eye tissue is initiated by a conserved set of transcription factors termed retinal determination network (RDN). In the fruit fly Drosophila melanogaster, the zinc-finger transcription factor Glass acts directly downstream of the RDN to control identity of photoreceptor as well as non-photoreceptor cells. Tight control of spatial and temporal gene expression is a critical feature during development, cell-fate determination as well as maintenance of differentiated tissues. The molecular mechanisms that control expression of glass, however, remain largely unknown. We here identify complex regulatory mechanisms controlling expression of the glass locus. All information to recapitulate glass expression are contained in a compact 5.2 kb cis-acting genomic element by combining different cell-type specific and general enhancers with repressor elements. Moreover, the immature RNA of the locus contains an alternative small open reading frame (smORF) upstream of the actual glass translation start, resulting in a small peptide instead of the three possible Glass protein isoforms. CRISPR/Cas9-based mutagenesis shows that the smORF is not required for the formation of functioning photoreceptors, but is able to attenuate effects of glass misexpression. Furthermore, editing the genome to generate glass loci eliminating either one or two isoforms shows that only one of the three proteins is critical for formation of functioning photoreceptors, while removing the two other isoforms did not cause defects in developmental or photoreceptor function. Our results show that eye development and function is largely unaffected by targeted manipulations of critical features of the glass transcript, suggesting a strong selection pressure to allow the formation of a functioning eye.

A comparative map of macroautophagy and mitophagy in the vertebrate eye

Photoreception is pivotal to our experience and perception of the natural world; hence the eye is of prime importance for most vertebrate animals to sense light. Central to visual health is mitochondrial homeostasis, and the selective autophagic turnover of mitochondria (mitophagy) is predicted to play a key role here. Despite studies that link aberrant mitophagy to ocular dysfunction, little is known about the prevalence of basal mitophagy, or its relationship to general autophagy, in the visual system. In this study, we utilize the mito-QC mouse and a closely related general macroautophagy reporter model to profile basal mitophagy and macroautophagy in the adult and developing eye. We report that ocular macroautophagy is widespread, but surprisingly mitophagy does not always follow the same pattern of occurrence. We observe low levels of mitophagy in the lens and ciliary body, in stark contrast to the high levels of general MAP1LC3-dependent macroautophagy in these regions. We uncover a striking reversal of this process in the adult retina, where mitophagy accounts for a larger degree of the macroautophagy taking place, specifically in the photoreceptor neurons of the outer nuclear layer. We also show the developmental regulation of autophagy in a variety of ocular tissues. In particular, mitophagy in the adult mouse retina is reversed in localization during the latter stages of development. Our work thus defines the landscape of mitochondrial homeostasis in the mammalian eye, and in doing so highlights the selective nature of autophagy in vivo and the specificity of the reporters used. Abbreviations: ATG: autophagy related; GFP: green fluorescent protein; LC3: microtubule associated protein 1 light chain 3; ONH: optic nerve head; ONL: outer nuclear layer; RPE: retinal pigment epithelium.

DEAD-box RNA helicase Belle posttranscriptionally promotes gene expression in an ATPase activity-dependent manner

Drosophila Belle (human ortholog DDX3) is a conserved DEAD-box RNA helicase implicated in regulating gene expression. However, the molecular mechanisms by which Belle/DDX3 regulates gene expression are poorly understood. Here we performed systematic mutational analysis to determine the contributions of conserved motifs within Belle to its in vivo function. We found that Belle RNA-binding and RNA-unwinding activities and intrinsically disordered regions (IDRs) are required for Belle in vivo function. Expression of Belle ATPase mutants that cannot bind, hydrolyze, or release ATP resulted in dominant toxic phenotypes. Mechanistically, we discovered that Belle up-regulates reporter protein level when tethered to reporter mRNA, without corresponding changes at the mRNA level, indicating that Belle promotes translation of mRNA that it binds. Belle ATPase activity and amino-terminal IDR were required for this translational promotion activity. We also found that ectopic ovary expression of dominant Belle ATPase mutants decreases levels of cyclin proteins, including Cyclin B, without corresponding changes in their mRNA levels. Finally, we found that Belle binds endogenous cyclin B mRNA. We propose that Belle promotes translation of specific target mRNAs, including cyclin B mRNA, in an ATPase activity-dependent manner.

Neurodevelopmental Outcomes after Intravitreal Bevacizumab Therapy for Retinopathy of Prematurity: A Prospective Case-Control Study

PURPOSE

To evaluate the neurodevelopmental and ocular developmental outcomes in premature children who have undergone intravitreal bevacizumab injection (IVB) for treatment of type 1 retinopathy of prematurity (ROP).

DESIGN

Prospective case-control study.

PARTICIPANTS

We enrolled 3 groups of premature patients: premature children who had no history of ROP (group 0), premature children with history of ROP without treatment (group 1), and premature children with ROP who had received a single IVB (0.625 mg; group 2).

METHODS

Ocular developmental assessment, including cycloplegic refractometry, axial length, Cardiff acuity, and neurodevelopmental assessment via the Bayley Scales of Infant and Toddler Development, Third Edition (Bayley III), were performed at 1 to 3 years of age and were compared between groups.

MAIN OUTCOME MEASURES

Ocular developmental outcomes and Bayley III scores.

RESULTS

A total of 148 patients (85 boys and 63 girls) were included. The mean age at assessment was 1.49±0.59 years. Group 0 patients demonstrated significantly higher gestational age (GA), birth weight, and Apgar scores compared with group 1 and 2 patients. There were no significant differences between groups 1 and 2 in demographics or systemic risk factors except for lower GA in group 2. The cylindrical power was significantly larger in groups 1 and 2 compared with group 0. The spherical equivalent was significantly more myopic and the Cardiff acuity was significantly poorer in group 2 than in group 0. There were no significant differences between groups 1 and 2 in refractive status, axial length, or Cardiff acuity. Neurodevelopmental assessment using Bayley III showed no significant difference among the 3 groups in any aspect after adjusting for GA and other systemic risk factors. The risks for poor neurodevelopmental outcomes also were not significantly different.

CONCLUSIONS

At the mean age of 1.5 years, children with prior history of IVB (group 2) showed similar refractive and visual outcomes and similar neurodevelopmental outcomes compared with premature patients with ROP without requirement of treatment (group 1), although there is a possibility that a small but clinically significant difference may not have been detected in the current study.

Predation selects for smaller eye size in a vertebrate: effects of environmental conditions and sex

Increased eye size in animals results in a larger retinal image and thus improves visual acuity. Thus, larger eyes should aid both in finding food as well as detecting predators. On the other hand, eyes are usually very conspicuous and several studies have suggested that eye size is associated with predation risk. However, experimental evidence is scant. In this study, we address how predation affects variation in eye size by performing two experiments using Eurasian perch juveniles as prey and either larger perch or pike as predators. First, we used large outdoor tanks to compare selection due to predators on relative eye size in open and artificial vegetated habitats. Second, we studied the effects of both predation risk and resource levels on phenotypic plasticity in relative eye size in indoor aquaria experiments. In the first experiment, we found that habitat altered selection due to predators, since predators selected for smaller eye size in a non-vegetated habitat, but not in a vegetated habitat. In the plasticity experiment, we found that fish predators induced smaller eye size in males, but not in females, while resource levels had no effect on eye size plasticity. Our experiments provide evidence that predation risk could be one of the driving factors behind variation in eye size within species.

Trimethyltin chloride induces reactive oxygen species-mediated apoptosis in retinal cells during zebrafish eye development

Trimethyltin chloride (TMT), one of the most widely used organotin compounds in industrial and agricultural fields, is widespread in soil, aquatic systems, foodstuffs and household items. TMT reportedly has toxic effects on the nervous system; however, there is limited information about its effects on eye development and no clear associated mechanisms have been identified. Therefore, in the present study, we investigated eye morphology, vison-related behavior, reactive oxygen species (ROS) production, apoptosis, histopathology, and gene expression to evaluate the toxicity of TMT during ocular development in zebrafish embryos. Exposure to TMT decreased the axial length and surface area of the eye and impaired the ability of zebrafish to recognize light. 2',7'-dichlorofluorescein diacetate and acridine orange assays revealed dose-dependent increases in ROS formation and apoptosis in the eye. Furthermore, pyknosis of retinal cells was confirmed through histopathological analysis. Antioxidative enzyme-related genes were downregulated and apoptosis-inducing genes were upregulated in TMT-treated zebrafish compared to expression in controls. Retinal cell-specific gene expression was suppressed mainly in retinal ganglion cells, bipolar cells, and photoreceptor cells, whereas amacrine cell-, horizontal cell-, and Müller cell-specific gene expression was enhanced. Our results demonstrate for the first time the toxicity of TMT during eye development, which occurs through the induction of ROS-mediated apoptosis in retinal cells during ocular formation.

Eye organogenesis: A hierarchical view of ocular development

This chapter provides an overview of the early developmental origins of six ocular tissues: the cornea, lens, ciliary body, iris, neural retina, and retina pigment epithelium. Many of these tissue types are concurrently specified and undergo a complex set of morphogenetic movements that facilitate their structural interconnection. Within the context of vertebrate eye organogenesis, we also discuss the genetic hierarchies of transcription factors and signaling pathways that regulate growth, patterning, cell type specification and differentiation.

Effects of Deepwater Horizon crude oil on ocular development in two estuarine fish species, red drum (Sciaenops ocellatus) and sheepshead minnow (Cyprinodon variegatus)

Polycyclic aromatic hydrocarbons (PAHs) present in crude oil have been shown to cause the dysregulation of genes important in eye development and function, as well as morphological abnormalities of the eye. However, it is not currently understood how these changes in gene expression are manifested as deficits in visual function. Embryonic red drum (Sciaenops ocellatus) and sheepshead minnow (Cyprinodon variegatus) were exposed to water accommodated fractions (WAFs) of weathered crude oil and assessed for visual function using an optomotor response assay in early life-stage larvae, with subsequent samples taken for histological analysis of the eyes. Larvae of both species exposed to increasing concentrations of oil exhibited a reduced optomotor response. The mean diameters of retinal layers, which play an important role in visual function and image processing, were significantly reduced in oil-exposed sheepshead larvae, though not in red drum larvae. The present study provides evidence that weathered crude oil has a significant effect on visual function in early life-stage fishes.

A transcriptomics analysis of the Tbx5 paralogues in zebrafish

TBX5 is essential for limb and heart development. Mutations in TBX5 are associated with Holt-Oram syndrome in humans. Due to the teleost specific genome duplication, zebrafish have two copies of TBX5: tbx5a and tbx5b. Both of these genes are expressed in regions of the lateral plate mesoderm and retina. In this study, we perform comparative RNA sequencing analysis on zebrafish embryos during the stages of lateral plate mesoderm migration. This work shows that knockdown of the Tbx5 paralogues results in altered gene expression in many tissues outside of the lateral plate mesoderm, especially in the somitic mesoderm and the intermediate mesoderm. Specifically, knockdown of tbx5b results in changes in somite size, in the differentiation of vasculature progenitors and in later patterning of trunk blood vessels.

Patterning the insect eye: From stochastic to deterministic mechanisms

While most processes in biology are highly deterministic, stochastic mechanisms are sometimes used to increase cellular diversity. In human and Drosophila eyes, photoreceptors sensitive to different wavelengths of light are distributed in stochastic patterns, and one such patterning system has been analyzed in detail in the Drosophila retina. Interestingly, some species in the dipteran family Dolichopodidae (the “long legged” flies, or “Doli”) instead exhibit highly orderly deterministic eye patterns. In these species, alternating columns of ommatidia (unit eyes) produce corneal lenses of different colors. Occasional perturbations in some individuals disrupt the regular columns in a way that suggests that patterning occurs via a posterior-to-anterior signaling relay during development, and that specification follows a local, cellular-automaton-like rule. We hypothesize that the regulatory mechanisms that pattern the eye are largely conserved among flies and that the difference between unordered Drosophila and ordered dolichopodid eyes can be explained in terms of relative strengths of signaling interactions rather than a rewiring of the regulatory network itself. We present a simple stochastic model that is capable of explaining both the stochastic Drosophila eye and the striped pattern of Dolichopodidae eyes and thereby characterize the least number of underlying developmental rules necessary to produce both stochastic and deterministic patterns. We show that only small changes to model parameters are needed to also reproduce intermediate, semi-random patterns observed in another Doli species, and quantification of ommatidial distributions in these eyes suggests that their patterning follows similar rules.

A simple model is able to account for a diversity of photoreceptor patterns in different fly species, ranging from highly deterministic to fully random.

Visual Function and Fundus Morphology in Relation to Growth and Cardiovascular Status in 10-Year-Old Moderate-to-Late Preterm Children

PURPOSE

To study visual function and ocular fundus morphology in relation to growth, metabolic status, and blood pressure in moderate-to-late preterm (MLP) children at 10 years of age.

DESIGN

Prospective cohort study.

METHODS

In this population-based observational study, nonsyndromic MLP children born in Gothenburg, Sweden, were examined neonatally in the years 2002-2003 concerning length, weight, head circumference, and insulin-like growth factor I (IGF-I). At 10 years of age, 33 children (10 girls) were examined regarding previously mentioned variables, and regarding visual acuity, refraction, fundus morphology, IGF binding protein 3, leptin, adiponectin, and blood pressure. An age- and sex-matched control group consisted of 28 children (9 girls).

RESULTS

Myopia was more commonly found in MLP children than in controls (P = .004, 95% CI 1.8 to 49.8). The MLP group had smaller optic disc area (P = .01, 95% CI -0.5 to -0.1), smaller rim area (P = .001, 95% CI -0.5 to -0.2), fewer branching points (P = .0001, 95% CI -5.7 to -2.1), and higher index of tortuosity of arteries (P = .03, 95% CI 0.002 to 0.03) and veins (P = .02, 95% CI 0.003 to 0.02). Refraction correlated with IGF-I (P = .0005, r_s = 0.60 in right eye, and P = .002, r_s = 0.55 in left eye) at 10 years of age. Tortuosity of arteries at assessment correlated with neonatal IGF-I levels (P = .03, r_s = -0.39). Tortuosity of veins correlated with a leptin/adiponectin ratio at assessment (P = .04, r_s = 0.37).

CONCLUSION

The findings suggest that being born MLP is associated with myopia, smaller optic disc and rim areas, and abnormal retinal vascularization. Furthermore, metabolic status and growth factors seem to have an impact on ocular development.

Effects of glucocorticoid on the eye development in guinea pigs

Glucocorticoid (GC) has been widely used in clinic. However, the effect of GC on normal and myopic development of eyes is still unknown. In this study, 3-week-old guinea pigs were randomly divided into four groups: No-Lens (control), GC+No-Lens, negative lens-induced myopia (LIM), and GC+LIM. To induce myopia, right eyes were covered with a -10 D lens in GC+LIM and LIM groups. GC+No-Lens and GC+LIM groups received intraperitoneal injections of hydrocortisone (10 mg/kg) once daily for 2 weeks, and then received intragastric hydrocortisone (32.5 mg/kg) every other day for the next 4 weeks, while No-Lens (control) and LIM groups were injected intraperitoneally with saline for 2 weeks, and then given saline by intragastric administertion for the next 4 weeks. Several parameters were assessed: ocular axial length and refractive error, sclera thickness, matrix metalloprotein-2 (MMP-2) and tissue inhibitor metalloprotease-2 (TIMP-2) expressions and localization of the posterior sclera, plasma concentrations of free triiodothyronine (FT3), free thyroxine (FT4), testosterone (T), and oestradiol (E2). Results indicated that: (1) in normal eye development, hydrocortisone could inhibit both the axial elongation and the myopic shift; whereas (2) in LIM eye development, hydrocortisone (a) enhanced the axial elongation, myopic shift and sclera thinning; (b) enhanced the MMP-2 expression and decreased TIMP-2 expression, and (c) elevated the plasma concentration of E2 but decreased the levels of FT3, FT4, and T. In conclusion, glucocorticoid may influence both normal and LIM eye development. The balance of the hormones is fundamental for the eye development.

Gene expression in response to optical defocus of opposite signs reveals bidirectional mechanism of visually guided eye growth

Myopia (nearsightedness) is the most common eye disorder, which is rapidly becoming one of the leading causes of vision loss in several parts of the world because of a recent sharp increase in prevalence. Nearwork, which produces hyperopic optical defocus on the retina, has been implicated as one of the environmental risk factors causing myopia in humans. Experimental studies have shown that hyperopic defocus imposed by negative power lenses placed in front of the eye accelerates eye growth and causes myopia, whereas myopic defocus imposed by positive lenses slows eye growth and produces a compensatory hyperopic shift in refractive state. The balance between these two optical signals is thought to regulate refractive eye development; however, the ability of the retina to recognize the sign of optical defocus and the composition of molecular signaling pathways guiding emmetropization are the subjects of intense investigation and debate. We found that the retina can readily distinguish between imposed myopic and hyperopic defocus, and identified key signaling pathways underlying retinal response to the defocus of different signs. Comparison of retinal transcriptomes in common marmosets exposed to either myopic or hyperopic defocus for 10 days or 5 weeks revealed that the primate retina responds to defocus of different signs by activation or suppression of largely distinct pathways. We also found that 29 genes differentially expressed in the marmoset retina in response to imposed defocus are localized within human myopia quantitative trait loci (QTLs), suggesting functional overlap between genes differentially expressed in the marmoset retina upon exposure to optical defocus and genes causing myopia in humans. These findings identify retinal pathways involved in the development of myopia, as well as potential new strategies for its treatment.

The worldwide prevalence of myopia is predicted to increase from the current 23% to about 50% in the next three decades. Although much effort has been directed towards elucidating the mechanisms underlying refractive eye development and myopia, treatment options for myopia are mostly limited to optical correction, which does not prevent progression of myopia nor the pathological blinding complications often associated with the disease. Several experimental optics-based treatments have had only limited effect on myopia progression, and currently available drug treatments are limited and the mechanisms of action are not well understood. The development of safe and effective pharmacological treatments for myopia is urgently needed to prevent the impending myopia epidemic. The main obstacles that prevent the development of anti-myopia drugs are the uncertainties regarding the mechanisms controlling eye growth and optical development, including the molecular signaling pathways underlying it. In this study, we show that, contrary to the conventional thinking that myopic and hyperopic defocus trigger opposite changes in the same genes and pathways to guide postnatal eye growth, defocus of opposite signs affect eye growth via largely distinct retinal pathways. Knowing that myopic and hyperopic defocus signals drive eye growth in opposite directions and propagate via different pathways provides a framework for the development of new anti-myopia drugs. Myopia can be controlled pharmacologically by stimulating pathways underlying the retinal response to positive lenses and/or by suppressing pathways underlying the retinal response to negative lenses.

Elimination of Signaling by the Luteinizing Hormone Receptor Reduces Ocular VEGF and Retinal Vascularization during Mouse Eye Development

Purpose/Aim: Vascular endothelial growth factor (VEGF) dysregulation is implicated in the pathogenesis of retinopathy of prematurity (ROP). Identifying the factors that contribute to VEGF regulation during normal retinal vascularization is the key to ROP prevention. Currently, physiologic hypoxia is thought to be responsible for retinal VEGF regulation in utero. However, a potential hormonal contribution to VEGF regulation during eye development has not been fully investigated. The placental hormone, human chorionic gonadotropin and the pituitary hormone, and luteinizing hormone (LH) induce VEGF expression in several tissue types. Both of these gonadotropins activate the same LH receptor (LHR) in the human body; LHRs are expressed in the retina. In this study, we aimed to show that LHR signaling participates in VEGF regulation in the developing eye.

METHODS

When offspring from breeding pairs of LHR knockout mice (lhrkos) reached 21 days old, eyes and serum were extracted from homozygote lhrkos and wildtype (WT) siblings. VEGF levels were measured using Mouse VEGF Quantikine immunoassay kit. Retinas were incubated with isolectin for endothelial cell staining, flat mounted and imaged by confocal microscopy. Retinal vascular density was quantified using Imaris software. Some eyes were sectioned and stained for histopathologic review.

RESULTS

Ocular VEGF and retinal vascular volumes were significantly reduced by ~ 15% in lhrko eyes. Serum VEGF was not changed. The lhrko retinas did not display any anomalies.

CONCLUSIONS

We provide evidence that LHR signaling plays a role in VEGF regulation and vascularization in the developing eye. Given that human preterm infants may have altered LHR-activity, the effect of gonadotropins on eye development should be further studied to identify novel strategies for ROP prevention.

Long-term development of refractive error in refractive, nonrefractive and partially accommodative esotropia

Accommodative esotropia (AE) is a convergent deviation due to an excess of the convergence linked to the innervational stimulus for accommodation and it is usually associated to the presence of hyperopia. The development of hyperopia over time has been widely described but the lack of comparative analysis among accommodative esotropia subtypes, does not allow to verify the existence of different developmental patterns. In this study we aimed to describe the long term changes of refractive error in patients affected by accommodative esotropia as a function of the strabismus type: refractive (RAE), non-refractive (NRAE) and partially accommodative esotropia (PAE). The medical records of 66 patients (24 RAE, 22 PAE, 20 NRAE), who wore the full correction of their cycloplegic refraction error during the entire follow up period, were retrospectively reviewed. Mean outcome was the analysis of the variations, among groups, of refractive error over time; differences between mild (≤3.00D) and high (≥5.00D) hyperopia, effects of amblyopia and relationship with AC/A ratio were also investigated. All patients were followed up from approximately 4 years of age to 20, with mean follow up of 16.06±0.29 years. Our results described similar non-linear trend of refractive error development among groups. The initial increase of hyperopia (up to 7–8 years) was followed by a decreasing trend persisting up to adulthood (approximately 20 years of age). During this period, spherical equivalent decreased at a lower mean annual rate in patients affected by RAE (-0.07D) compared to other groups (NRAE -0.11D, p = 0.003 and PAE 0.13D, p = 0.002). In all groups, however, significant amount of hyperopia was found at last examination; indeed the observed difference in SE values from baseline to the end of follow up, was not significant (RAE: +0.27D, 95% C.I. -0.49 to +1.04D, p = 0.472; PAE: -0.69D, 95% C.I. -1.67 to +0.28D, p = 0.154; NRAE: -0.39D, 95% C.I. -1.11 to +0.34D, p = 0.278). AC/A ratio, amblyopia and amount of initial hyperopia appeared to have no significant role in longitudinal change of the refractive error. In conclusion, this study provides a complete overview, from childhood to adulthood, of refractive error development in different form of accommodative esotropia.

Molecular cloning and functional expression of the 5-HT7 receptor in Chinese mitten crab (Eriocheir sinensis)

Serotonin (5-HT) regulates numerous physiological functions and processes, such as light adaptation, food intake and ovarian maturation, and plays the role through 5-HT receptors. To our knowledge, this is the first study to isolate and characterize the serotonin receptor 7 (5-HT₇ receptor) cDNA encoded in Eriocheir sinensis, an economically important aquaculture species in China, by performing rapid-amplification of cDNA ends. The full-length of 5-HT₇ receptor gene cDNA is 2328 bp and encodes a polypeptide with 590 amino acids that are highly homologous with other crustaceans 5-HT₇ receptor genes. Analysis of the deduced amino acid sequence of the 5-HT₇, including 7 transmembrane domains and some common features of G protein-coupled receptors (GPCRs), indicated that 5-HT₇ receptor was a member of GPCRs family. A gene expression analysis of the 5-HT₇ receptor by RT-PCR revealed that the 5-HT₇ receptor transcripts were widely distributed in various tissues, in which high expression levels were observed in the cranial ganglia, thoracic ganglia and intestines. Further study about the effects of photoperiods on the 5-HT₇ expression in the tissues showed that a significantly increasing expression of the 5-HT₇ receptor was observed in the thoracic ganglia induced by constant light. In addition, in the eyestalks, the expression levels of 5-HT₇ mRNA in constant darkness and constant light were lower than control treatment. Then, the expression levels of the 5-HT₇ receptor in three feeding statuses displayed that there were significantly increasing expressions in the hepatopancreas and intestines after feeding, compared with before feeding and during the feeding period. Finally, the 5-HT₇ mRNA expression levels in stage III and stage IV were higher than the levels in stage I of ovarian development. Our experimental results showed that the 5-HT₇ receptor structurally belongs to GPCRs, and the thoracic ganglia and eyestalks are the important tissues of the 5-HT₇ receptor for light adaptation. The 5-HT₇ receptor may also be involved in the physiological regulation of the hepatopancreas and intestines after ingestion in E. sinensis. In addition, the 5-HT₇ receptor is involved in the process of ovarian maturation. The study provided a foundation for further research of light adaptation, digestive functions and ovarian maturation of the 5-HT₇ receptor in Decapoda.

Histological development of the long-snouted seahorse Hippocampus guttulatus during ontogeny

The objective of the present study was to describe histological development of the European long-snouted seahorse Hippocampus guttulatus, to increase understanding of the biology and physiology of the species. Most vital organs were present in juveniles by the time of their release from the male's pouch. Digestive tract specialization occurred at 89 effective day-degrees (D°_eff ), corresponding to 15 days post partum (dpp), with development of the first intestinal loop and mucosal folding. At 118 D°_eff (20 dpp), lipids were being mobilized from the liver and oocytes attained the perinuclear stage. The fovea emerged at 177 D°_eff (30 dpp), contemporaneous with the shift from pelagic to benthic behaviour in juveniles. At this stage, the most interesting feature was the formation of the second intestinal loop. Male gonads were never observed during the study (from 0 to 354 D°_eff ; 0-60 dpp), but the first oogonia were present at 30 D°_eff (5 dpp). In 354 D°_eff (60 dpp) juveniles, oocytes were observed in a cortical alveoli stage, indicating maturity. Low digestive efficiency was observed at early stages, which was due to a poorly developed gastrointestinal tract and an immature digestive tract prior to 89 D°_eff . The present study demonstrates that approximately 89 and 177 D°_eff represent two important transitional stages in the early development of H. guttulatus. At a temperature of approximately 19 ± 1°C and an age of 1 month (177 D°_eff ), main organs were fully functional, suggesting that the adult phenotype was largely established by that age, with females becoming mature at the age of 2 months (354 D°_eff ).

Circadian rhythms, refractive development, and myopia

PURPOSE

Despite extensive research, mechanisms regulating postnatal eye growth and those responsible for ametropias are poorly understood. With the marked recent increases in myopia prevalence, robust and biologically-based clinical therapies to normalize refractive development in childhood are needed. Here, we review classic and contemporary literature about how circadian biology might provide clues to develop a framework to improve the understanding of myopia etiology, and possibly lead to rational approaches to ameliorate refractive errors developing in children.

RECENT FINDINGS

Increasing evidence implicates diurnal and circadian rhythms in eye growth and refractive error development. In both humans and animals, ocular length and other anatomical and physiological features of the eye undergo diurnal oscillations. Systemically, such rhythms are primarily generated by the 'master clock' in the surpachiasmatic nucleus, which receives input from the intrinsically photosensitive retinal ganglion cells (ipRGCs) through the activation of the photopigment melanopsin. The retina also has an endogenous circadian clock. In laboratory animals developing experimental myopia, oscillations of ocular parameters are perturbed. Retinal signaling is now believed to influence refractive development; dopamine, an important neurotransmitter found in the retina, not only entrains intrinsic retinal rhythms to the light:dark cycle, but it also modulates refractive development. Circadian clocks comprise a transcription/translation feedback control mechanism utilizing so-called clock genes that have now been associated with experimental ametropias. Contemporary clinical research is also reviving ideas first proposed in the nineteenth century that light exposures might impact refraction in children. As a result, properties of ambient lighting are being investigated in refractive development. In other areas of medical science, circadian dysregulation is now thought to impact many non-ocular disorders, likely because the patterns of modern artificial lighting exert adverse physiological effects on circadian pacemakers. How, or if, such modern light exposures and circadian dysregulation contribute to refractive development is not known.

SUMMARY

The premise of this review is that circadian biology could be a productive area worthy of increased investigation, which might lead to the improved understanding of refractive development and improved therapeutic interventions.

Hippo Signaling Circuit and Divergent Tissue Growth in Mammalian Eye

Vertebrate organ development is accompanied by demarcation of tissue compartments, which grow coordinately with their neighbors. Hence, perturbing the coordinative growth of neighboring tissue compartments frequently results in organ malformation. The growth of tissue compartments is regulated by multiple intercellular and intracellular signaling pathways, including the Hippo signaling pathway that limits the growth of various organs. In the optic neuroepithelial continuum, which is partitioned into the retina, retinal pigment epithelium (RPE) and ciliary margin (CM) during eye development, the Hippo signaling activity operates differentially, as it does in many tissues. In this review, we summarize recent studies that have explored the relationship between the Hippo signaling pathway and growth of optic neuroepithelial compartments. We will focus particularly on the roles of a tumor suppressor, neurofibromin 2 (NF2), whose expression is not only dependent on compartment-specific transcription factors, but is also subject to regulation by a Hippo-Yap feedback signaling circuit.

Patterning mechanisms diversify neuroepithelial domains in the Drosophila optic placode

The central nervous system develops from monolayered neuroepithelial sheets. In a first step patterning mechanisms subdivide the seemingly uniform epithelia into domains allowing an increase of neuronal diversity in a tightly controlled spatial and temporal manner. In Drosophila, neuroepithelial patterning of the embryonic optic placode gives rise to the larval eye primordium, consisting of two photoreceptor (PR) precursor types (primary and secondary), as well as the optic lobe primordium, which during larval and pupal stages develops into the prominent optic ganglia. Here, we characterize a genetic network that regulates the balance between larval eye and optic lobe precursors, as well as between primary and secondary PR precursors. In a first step the proneural factor Atonal (Ato) specifies larval eye precursors, while the orphan nuclear receptor Tailless (Tll) is crucial for the specification of optic lobe precursors. The Hedgehog and Notch signaling pathways act upstream of Ato and Tll to coordinate neural precursor specification in a timely manner. The correct spatial placement of the boundary between Ato and Tll in turn is required to control the precise number of primary and secondary PR precursors. In a second step, Notch signaling also controls a binary cell fate decision, thus, acts at the top of a cascade of transcription factor interactions to define PR subtype identity. Our model serves as an example of how combinatorial action of cell extrinsic and cell intrinsic factors control neural tissue patterning.

[Ocular surface aging: Pathophysiology and consequences for management]

All the components of the ocular surface and the lacrimal system are affected by aging. Aging induces lacrimal gland fibrosis, Meibomian gland dysfunction, loss of corneal sensitivity, decreased corneal cell density, impairment of immune defences, increased local inflammation associated with hormonal changes, conjunctivochalasis, lid abnormalities, etc. Furthermore, homeostasis of the ocular surface may be altered by various age-related systemic comorbidities and iatrogenic interventions. Altogether, aging is considered the most predominant risk factor for dry eye disease. The increasing knowledge of the pathophysiology of aging of the ocular surface allows for refinement of the management of ocular surface disease in the elderly.

Müller glia-derived PRSS56 is required to sustain ocular axial growth and prevent refractive error

A mismatch between optical power and ocular axial length results in refractive errors. Uncorrected refractive errors constitute the most common cause of vision loss and second leading cause of blindness worldwide. Although the retina is known to play a critical role in regulating ocular growth and refractive development, the precise factors and mechanisms involved are poorly defined. We have previously identified a role for the secreted serine protease PRSS56 in ocular size determination and PRSS56 variants have been implicated in the etiology of both hyperopia and myopia, highlighting its importance in refractive development. Here, we use a combination of genetic mouse models to demonstrate that Prss56 mutations leading to reduced ocular size and hyperopia act via a loss of function mechanism. Using a conditional gene targeting strategy, we show that PRSS56 derived from Müller glia contributes to ocular growth, implicating a new retinal cell type in ocular size determination. Importantly, we demonstrate that persistent activity of PRSS56 is required during distinct developmental stages spanning the pre- and post-eye opening periods to ensure optimal ocular growth. Thus, our mouse data provide evidence for the existence of a molecule contributing to both the prenatal and postnatal stages of human ocular growth. Finally, we demonstrate that genetic inactivation of Prss56 rescues axial elongation in a mouse model of myopia caused by a null mutation in Egr1. Overall, our findings identify PRSS56 as a potential therapeutic target for modulating ocular growth aimed at preventing or slowing down myopia, which is reaching epidemic proportions.