The role of Pax-6 in eye and nasal development

Coexistence of congenital lacrimal gland agenesis and congenital aniridia: Case report

Purpose

To document a rare case of congenital aniridia due to paired box gene 6 (PAX6), elongated protein 4 (ELP4) and fusion gene DKFZp686k1684 mutation with bilateral congenital lacrimal gland agenesis and multiple ocular comorbidities, aiming to expand the understanding of its clinical presentations and therapeutic interventions.

Observations

A 10-year-old female presented with severe dry eyes and photophobia, with no tears since birth in both eyes. Diagnosed with sporadic aniridia, previously the patient developed secondary glaucoma requiring multiple surgeries in both eyes. Examination revealed severe dry eyes, foveal hypoplasia, aniridia-associated keratopathy, and was suspicious for absence of lacrimal gland with no palpebral lobe evident on bilateral external inspection. Magnetic resonance imaging revealed lacrimal gland hypoplasia of the right eye and lacrimal gland agenesis of the left eye. Over 10 years, the patients' condition was managed with punctal plugs and artificial tears allowing for stable vision with resolution of bilateral superficial punctate keratitis. Whole genome sequence analysis revealed a large deletion in chromosome 11p13 including the whole PAX6 gene, ELP4 and fusion gene DKFZp686k1684.

Conclusion and importance

This case illustrates an association between congenital aniridia and lacrimal gland agenesis. The findings highlight the complexity of genetic influences on ocular development and the importance of early identification and management to prevent complications.

Making sense of vertebrate senses from a neural crest and cranial placode evo-devo perspective

The evolution of vertebrates from protochordate ancestors marked the beginning of the gradual transition to predatory lifestyles. Enabled by the acquisition of multipotent neural crest and cranial placode cell populations, vertebrates developed an elaborate peripheral nervous system, equipped with paired sense organs, which aided in adaptive behaviors and ultimately, successful colonization of diverse environmental niches. Underpinning the enduring success of vertebrates is the highly adaptable nature of the peripheral nervous system, which is enabled by the exceptional malleability of the neural crest and placode developmental programs. Here, we explore the embryonic origins of the vertebrate senses from the neural crest and cranial placodes and discuss the evolutionary trajectory of the senses in the context of adaptation to novel environments.

Histological analysis of anterior eye development in the brown anole lizard (Anolis sagrei)

For all vertebrates, the anterior eye structures work together to protect and nourish the eye while ensuring that light entering the eye is correctly focused on the retina. However, the anterior eye structure can vary significantly among different vertebrates, reflecting how the structures of the anterior eye have evolved to meet the specific visual needs of different vertebrate species. Although conserved pathways regulate fundamental aspects of anterior eye development in vertebrates, there may also be species-specific differences underlying structural variation. Our knowledge of the cellular and molecular mechanisms underlying the development of structures of the anterior eye comes mainly from work in mammals, chicks, some amphibians, and small teleosts such as zebrafish. Our understanding of anterior eye development would benefit from comparative molecular studies in diverse vertebrates. A promising lizard model is the brown anole, Anolis sagrei, which is easily raised in the laboratory and for which genome editing techniques exist. Here, we provide a detailed histological analysis of the development of the anterior structures of the eye in A. sagrei, which include the cornea, iris, ciliary body, lens, trabecular meshwork, and scleral ossicles. The development of the anterior segment in anoles follows a pattern similar to other vertebrates. The lens forms first, followed by the cornea, iris, ciliary body, and tissues involved in the outflow of the aqueous humor. The development of the iris and ciliary body begins temporally and then proceeds nasally. Scleral ossicle development is generally comparable to that reported for chicks and turtles. Anoles have a remarkably thin cornea and a flat ciliary body compared to the eyes of mammals and birds. This study highlights several features in anoles and represents a deeper understanding of reptile eye development.

Network analysis reveals potential mechanisms that determine the cellular identity of keratinocytes and corneal epithelial cells through the Hox/Gtl2-Dio3 miRNA axis

During embryonic development, both corneal epithelial cells (CECs) and keratinocytes (KCs) originate from the surface ectoderm. As a result of this shared origin, corneal epithelial cells may exhibit the same characteristics as the skin epidermis in pathological situations, while keratinocytes are ideal seed cells for tissue-engineered corneas. However, how the identities of keratinocytes and corneal epithelial cells are determined is currently unclear. In this study, to investigate the molecular mechanisms determining the identity of keratinocytes and corneal epithelial cells, small RNA and mRNA sequencing analyses of these two cell types were performed. Analysis of the sequencing data revealed that almost all the miRNAs in the Gtl2-Dio3 imprinting region were highly expressed in keratinocytes and accounted for 30% of all differentially expressed miRNAs (DEMs). Since all the genes in the Gtl2-Dio3 imprinting region form a long polycistronic RNA under the control of the Gtl2 promoter, we next examined the expression of transcription factors and their binding near the Gtl2 locus. The findings indicated that the homeobox family dominated the differentially expressed transcription factors, and almost all Hox genes were silenced in corneal epithelial cells. Transcription binding site prediction and ChIP-seq revealed the binding of Hox proteins near the Gtl2 locus. Analysis of the Gtl-Dio3 miRNA target genes indicated that these miRNAs mainly regulate the Wnt signaling pathway and the PI3K-Akt signaling pathway. The crucial transcription factors in corneal epithelial cells, Pax6, Otx2, and Foxc1, are also targets of Gtl-Dio3 miRNAs. Our study revealed potential mechanisms that determine the cellular identity of keratinocytes and corneal epithelial cells through the Hox/Gtl2-Dio3 miRNA axis, which provides a new perspective for understanding the developmental regulation of corneal epithelial cells and the mechanisms of corneal opacity, as well as for establishing the groundwork for promoting the transdifferentiation of keratinocytes into corneal epithelial cells.

Pax6 expressing neuroectodermal and ocular stem cells: Its role from a developmental biology perspective

Pax-6 emerges as a critical transcription factor that guides the fate of stem cells towards neural lineages. Its expression influences the differentiation of neural progenitors into diverse neuronal subtypes, glial cells, and other neural cell types. Pax-6 operates with other regulatory factors to ensure the precise patterning and organization of the developing nervous system. The intricate interplay between Pax-6 and other signaling pathways, transcription factors, and epigenetic modifiers underpins the complicated balance between stem cell maintenance, proliferation, and differentiation in neuroectodermal and ocular contexts. Dysfunction of Pax-6 can lead to a spectrum of developmental anomalies, underscoring its importance in these processes. This review highlights the essential role of Pax-6 expression in neuroectodermal and ocular stem cells, shedding light on its significance in orchestrating the intricate journey from stem cell fate determination to the emergence of diverse neural and ocular cell types. The comprehensive understanding of Pax-6 function gained from a developmental biology perspective offers valuable insights into normal development and potential therapeutic avenues for neuroectodermal and ocular disorders.

Positive selection in cilia-related genes may facilitate deep-sea adaptation of Thermocollonia jamsteci

Deep-sea hydrothermal vents are characterized by high hydrostatic pressure, hypoxia, darkness and toxic substances. However, how organisms adapt to such extreme marine ecosystems remain poorly understood. We hypothesize that adaptive evolution plays an essential role in generating novelty for evolutionary adaptation to the deep-sea environment because adaptive evolution has been found to be critical for species origin and evolution. In this project, the chromosome-level genome of the deep-sea hydrothermal vent gastropod T. jamsteci was constructed for the first time to examine molecular mechanisms of its adaptation to the deep-sea environment. The genome size was large (2.54 Gb), ranking at the top of all species in the Vetigastropoda subclass, driven primarily by the bursts of transposable elements (TEs). The transposition of TEs may also trigger chromosomal changes including both inter-chromosomal fusions and intra-chromosomal activities involving chromosome inversions, rearrangements and fusions, as revealed by comparing the genomes of T. jamsteci and its closely related shallow-sea species Gibbula magus. Innovative changes including the expansion of the ABC transporter gene family that may facilitate detoxification, duplication of genes related to endocytosis, immunity, apoptosis, and anti-apoptotic domains that may help T. jamsteci fight against microbial pathogens, were identified. Furthermore, comparative analysis identified positive selection signals in a large number of genes including the hypoxia up-regulated protein 1, which is a chaperone that may promote adaptation of the T. jamsteci to hypoxic deepsea environments, hox2, Rx2, Pax6 and cilia-related genes BBS1, BBS2, BBS9 and RFX4. Notably, because of the critical importance of cilia and IFT in development, positive selection in cilia-related genes may play a critical role in facilitating T. jamsteci to adapt to the high-pressure deep-sea ecosystem. Results from this study thus revealed important molecular clues that may facilitate further research on the adaptation of molluscs to deep-sea hydrothermal vents.

Congenital anterior segment ocular disorders: Genotype-phenotype correlations and emerging novel mechanisms

Development of the anterior segment of the eye requires reciprocal sequential interactions between the arising tissues, facilitated by numerous genetic factors. Disruption of any of these processes results in congenital anomalies in the affected tissue(s) leading to anterior segment disorders (ASD) including aniridia, Axenfeld-Rieger anomaly, congenital corneal opacities (Peters anomaly, cornea plana, congenital primary aphakia), and primary congenital glaucoma. Current understanding of the genetic factors involved in ASD remains incomplete, with approximately 50% overall receiving a genetic diagnosis. While some genes are strongly associated with a specific clinical diagnosis, the majority of known factors are linked with highly variable phenotypic presentations, with pathogenic variants in FOXC1, CYP1B1, and PITX2 associated with the broadest spectrum of ASD conditions. This review discusses typical clinical presentations including associated systemic features of various forms of ASD; the latest functional data and genotype-phenotype correlations related to 25 ASD factors including newly identified genes; promising novel candidates; and current and emerging treatments for these complex conditions. Recent developments of interest in the genetics of ASD include identification of phenotypic expansions for several factors, discovery of multiple modes of inheritance for some genes, and novel mechanisms including a growing number of non-coding variants and alleles affecting specific domains/residues and requiring further studies.

PAX6 protein in neuromasts of the lateral line system of salamanders (Eurycea)

PAX6 is well known as a transcription factor that drives eye development in animals as widely divergent as flies and mammals. In addition to its localization in eyes, PAX6 expression has been reported in the central nervous system, the pancreas, testes, Merkel cells, nasal epithelium, developing cells of the inner ear, and embryonic submandibular salivary gland. Here we show that PAX6 also appears to be present in the mechanosensory neuromasts of the lateral line system in paedomorphic salamanders of the genus Eurycea. Using immunohistochemistry and confocal microscopy to examine a limited number of larvae of two species, listed by the United States of America's federal government as threatened (E. nana) or endangered (E. rathbuni), we found that anti-PAX6 antibody labeled structures that were extranuclear, and labeling was most intense in the apical appendages of the hair cells of the neuromast. This extranuclear localization raises the possibility of an as yet undescribed function for PAX6 as a cytoskeleton-associated protein.

Ancestral role of Pax6 in chordate brain regionalization

The Pax6 gene is essential for eye and brain development across various animal species. Here, we investigate the function of Pax6 in the development of the anterior central nervous system (CNS) of the invertebrate chordate amphioxus using CRISPR/Cas9-induced genome editing. Specifically, we examined Pax6 mutants featuring a 6 bp deletion encompassing two invariant amino acids in the conserved paired domain, hypothesized to impair Pax6 DNA-binding capacity and gene regulatory functions. Although this mutation did not result in gross morphological changes in amphioxus larvae, it demonstrated a reduced ability to activate Pax6-responsive reporter gene, suggesting a hypomorphic effect. Expression analysis in mutant larvae revealed changes in gene expression within the anterior CNS, supporting the conserved role of Pax6 gene in brain regionalization across chordates. Additionally, our findings lend support to the hypothesis of a zona limitans intrathalamica (ZLI)-like region in amphioxus, suggesting evolutionary continuity in brain patterning mechanisms. ZLI region, found in both hemichordates and vertebrates, functions as a key signaling center and serves as a restrictive boundary between major thalamic regions.

Lens placode modulates extracellular matrix formation during early eye development

The role extracellular matrix (ECM) in multiple events of morphogenesis has been well described, little is known about its specific role in early eye development. One of the first morphogenic events in lens development is placodal thickening, which converts the presumptive lens ectoderm from cuboidal to pseudostratified epithelium. This process occurs in the anterior pre-placodal ectoderm when the optic vesicle approaches the cephalic ectoderm and is regulated by transcription factor Pax6 and secreted BMP4. Since cells and ECM have a dynamic relationship of interdependence and modulation, we hypothesized that the ECM evolves with cell shape changes during lens placode formation. This study investigates changes in optic ECM including both protein distribution deposition, extracellular gelatinase activity and gene expression patterns during early optic development using chicken and mouse models. In particular, the expression of Timp2, a metalloprotease inhibitor, corresponds with a decrease in gelatinase activity within the optic ECM. Furthermore, we demonstrate that optic ECM remodeling depends on BMP signaling in the placode. Together, our findings suggest that the lens placode plays an active role in remodeling the optic ECM during early eye development.

PAX6 promotes neuroendocrine phenotypes of prostate cancer via enhancing MET/STAT5A-mediated chromatin accessibility

BACKGROUND

Neuroendocrine prostate cancer (NEPC) is a lethal subset of prostate cancer which is characterized by neuroendocrine differentiation and loss of androgen receptor (AR) signaling. Growing evidence reveals that cell lineage plasticity is crucial in the failure of NEPC therapies. Although studies suggest the involvement of the neural transcription factor PAX6 in drug resistance, its specific role in NEPC remains unclear.

METHODS

The expression of PAX6 in NEPC was identified via bioinformatics and immunohistochemistry. CCK8 assay, colony formation assay, tumorsphere formation assay and apoptosis assay were used to illustrate the key role of PAX6 in the progression of in vitro. ChIP and Dual-luciferase reporter assays were conducted to confirm the binding sequences of AR in the promoter region of PAX6, as well as the binding sequences of PAX6 in the promoter regions of STAT5A and MET. For in vivo validation, the xenograft model representing NEPC subtype underwent pathological analysis to verify the significant role of PAX6 in disease progression. Complementary diagnoses were established through public clinical datasets and transcriptome sequencing of specific cell lines. ATAC-seq was used to detect the chromatin accessibility of specific cell lines.

RESULTS

PAX6 expression was significantly elevated in NEPC and negatively regulated by AR signaling. Activation of PAX6 in non-NEPC cells led to NE trans-differentiation, while knock-down of PAX6 in NEPC cells inhibited the development and progression of NEPC. Importantly, loss of AR resulted in an enhanced expression of PAX6, which reprogramed the lineage plasticity of prostate cancer cells to develop NE phenotypes through the MET/STAT5A signaling pathway. Through ATAC-seq, we found that a high expression level of PAX6 elicited enhanced chromatin accessibility, mainly through attenuation of H4K20me3, which typically causes chromatin silence in cancer cells.

CONCLUSION

This study reveals a novel neural transcription factor PAX6 could drive NEPC progression and suggest that it might serve as a potential therapeutic target for the management of NEPC.

Pluripotent stem cell-derived models of retinal disease: Elucidating pathogenesis, evaluating novel treatments, and estimating toxicity

Blindness poses a growing global challenge, with approximately 26% of cases attributed to degenerative retinal diseases. While gene therapy, optogenetic tools, photosensitive switches, and retinal prostheses offer hope for vision restoration, these high-cost therapies will benefit few patients. Understanding retinal diseases is therefore key to advance effective treatments, requiring in vitro models replicating pathology and allowing quantitative assessments for drug discovery. Pluripotent stem cells (PSCs) provide a unique solution given their limitless supply and ability to differentiate into light-responsive retinal tissues encompassing all cell types. This review focuses on the history and current state of photoreceptor and retinal pigment epithelium (RPE) cell generation from PSCs. We explore the applications of this technology in disease modelling, experimental therapy testing, biomarker identification, and toxicity studies. We consider challenges in scalability, standardisation, and reproducibility, and stress the importance of incorporating vasculature and immune cells into retinal organoids. We advocate for high-throughput automation in data acquisition and analyses and underscore the value of advanced micro-physiological systems that fully capture the interactions between the neural retina, RPE, and choriocapillaris.

Homeobox gene-encoded transcription factors in development and mature circadian function of the rodent pineal gland

Homeobox genes encode transcription factors that are widely known to control developmental processes. This is also the case in the pineal gland, a neuroendocrine brain structure devoted to nighttime synthesis of the hormone melatonin. Thus, in accordance with high prenatal gene expression, knockout studies have identified a specific set of homeobox genes that are essential for development of the pineal gland. However, as a special feature of the pineal gland, homeobox gene expression persists into adulthood, and gene product abundance exhibits 24 h circadian rhythms. Recent lines of evidence show that some homeobox genes even control expression of enzymes catalyzing melatonin synthesis. We here review current knowledge of homeobox genes in the rodent pineal gland and suggest a model for dual functions of homeobox gene-encoded transcription factors in developmental and circadian mature neuroendocrine function.

The PAX Genes: Roles in Development, Cancer, and Other Diseases

Since their 1986 discovery in Drosophila, Paired box (PAX) genes have been shown to play major roles in the early development of the eye, muscle, skeleton, kidney, and other organs. Consistent with their roles as master regulators of tissue formation, the PAX family members are evolutionarily conserved, regulate large transcriptional networks, and in turn can be regulated by a variety of mechanisms. Losses or mutations in these genes can result in developmental disorders or cancers. The precise mechanisms by which PAX genes control disease pathogenesis are well understood in some cases, but much remains to be explored. A deeper understanding of the biology of these genes, therefore, has the potential to aid in the improvement of disease diagnosis and the development of new treatments.

Lens Placode Modulates Extracellular Matrix Formation During Early Eye Development

The role extracellular matrix (ECM) in multiple events of morphogenesis has been well described, little is known about its specific role in early eye development. One of the first morphogenic events in lens development is placodal thickening, which converts the presumptive lens ectoderm from cuboidal to pseudostratified epithelium. This process occurs in the anterior pre-placodal ectoderm when the optic vesicle approaches the cephalic ectoderm. Since cells and ECM have a dynamic relationship of interdependence and modulation, we hypothesized that the ECM evolves with cell shape changes during lens placode formation. This study investigates changes in optic ECM including both protein distribution deposition, extracellular gelatinase activity and gene expression patterns during early optic development using chicken and mouse models. In particular, the expression of Timp2 , a metalloprotease inhibitor, corresponds with a decrease in gelatinase activity within the optic ECM. Furthermore, we demonstrate that optic ECM remodeling depends on BMP signaling in the placode. Together, our findings suggest that the lens placode plays an active role in remodeling the optic ECM during early eye development.

Making developmental sense of the senses, their origin and function

The primary senses-touch, taste, sight, smell, and hearing-connect animals with their environments and with one another. Aside from the eyes, the primary sense organs of vertebrates and the peripheral sensory pathways that relay their inputs arise from two transient stem cell populations: the neural crest and the cranial placodes. In this chapter we consider the senses from historical and cultural perspectives, and discuss the senses as biological faculties. We begin with the embryonic origin of the neural crest and cranial placodes from within the neural plate border of the ectodermal germ layer. Then, we describe the major chemical (i.e. olfactory and gustatory) and mechanical (i.e. vestibulo-auditory and somatosensory) senses, with an emphasis on the developmental interactions between neural crest and cranial placodes that shape their structures and functions.

Characterization of an eye field-like state during optic vesicle organoid development

Specification of the eye field (EF) within the neural plate marks the earliest detectable stage of eye development. Experimental evidence, primarily from non-mammalian model systems, indicates that the stable formation of this group of cells requires the activation of a set of key transcription factors. This crucial event is challenging to probe in mammals and, quantitatively, little is known regarding the regulation of the transition of cells to this ocular fate. Using optic vesicle organoids to model the onset of the EF, we generate time-course transcriptomic data allowing us to identify dynamic gene expression programmes that characterize this cellular-state transition. Integrating this with chromatin accessibility data suggests a direct role of canonical EF transcription factors in regulating these gene expression changes, and highlights candidate cis-regulatory elements through which these transcription factors act. Finally, we begin to test a subset of these candidate enhancer elements, within the organoid system, by perturbing the underlying DNA sequence and measuring transcriptomic changes during EF activation.

Signaling - transcription interactions in mouse retinal ganglion cells early axon pathfinding -a literature review

Sending an axon out of the eye and into the target brain nuclei is the defining feature of retinal ganglion cells (RGCs). The literature on RGC axon pathfinding is vast, but it focuses mostly on decision making events such as midline crossing at the optic chiasm or retinotopic mapping at the target nuclei. In comparison, the exit of RGC axons out of the eye is much less explored. The first checkpoint on the RGC axons' path is the optic cup - optic stalk junction (OC-OS). OC-OS development and the exit of the RGC pioneer axons out of the eye are coordinated spatially and temporally. By the time the optic nerve head domain is specified, the optic fissure margins are in contact and the fusion process is ongoing, the first RGCs are born in its proximity and send pioneer axons in the optic stalk. RGC differentiation continues in centrifugal waves. Later born RGC axons fasciculate with the more mature axons. Growth cones at the end of the axons respond to guidance cues to adopt a centripetal direction, maintain nerve fiber layer restriction and to leave the optic cup. Although there is extensive information on OC-OS development, we still have important unanswered questions regarding its contribution to the exit of the RGC axons out of the eye. We are still to distinguish the morphogens of the OC-OS from the axon guidance molecules which are expressed in the same place at the same time. The early RGC transcription programs responsible for axon emergence and pathfinding are also unknown. This review summarizes the molecular mechanisms for early RGC axon guidance by contextualizing mouse knock-out studies on OC-OS development with the recent transcriptomic studies on developing RGCs in an attempt to contribute to the understanding of human optic nerve developmental anomalies. The published data summarized here suggests that the developing optic nerve head provides a physical channel (the closing optic fissure) as well as molecular guidance cues for the pioneer RGC axons to exit the eye.

Early-life exposure to environmentally relevant concentrations of triclocarban impairs ocular development in zebrafish larvae

Triclocarban (TCC), is an antimicrobial component in personal care products and it is one of the emerging contaminants since it has been detected in various environmental matrices. Its presence in human cord blood, breast milk, and maternal urine raised issues about its possible impact on development and increased concerns about the safety of daily exposure. This study aims to provide additional information about the effects of zebrafish early-life exposure to TCC on eye development and visual function. Zebrafish embryos were exposed to two concentrations of TCC (5 and 50 μg/L) for 4 days. TCC-mediated toxicity was assessed in larvae at the end of exposure and in the long term (20 days post fertilization; dpf), through different biological end-points. The experiments showed that TCC exposure influences the retinal architecture. In 4 dpf treated larvae, we found a less organized ciliary marginal zone, a decrease in the inner nuclear and inner plexiform layers, and a decrease in the retinal ganglion cell layer. Photoreceptor and inner plexiform layers showed an increase in 20 dpf larvae at lower and both concentrations, respectively. The expression levels of two genes involved in eye development (mitfb and pax6a) were both decreased at the concentration of 5 μg/L in 4 dpf larvae, and an increase in mitfb was observed in 5 μg/L-exposed 20 dpf larvae. Interestingly, 20 dpf larvae failed to discriminate between visual stimuli, demonstrating notable visual perception impairments due to compound. The results prompt us to hypothesize that early-life exposure to TCC may have severe and potentially long-term effect on zebrafish visual function.

Multiomics Analysis Reveals Novel Genetic Determinants for Lens Differentiation, Structure, and Transparency

Recent advances in next-generation sequencing and data analysis have provided new gateways for identification of novel genome-wide genetic determinants governing tissue development and disease. These advances have revolutionized our understanding of cellular differentiation, homeostasis, and specialized function in multiple tissues. Bioinformatic and functional analysis of these genetic determinants and the pathways they regulate have provided a novel basis for the design of functional experiments to answer a wide range of long-sought biological questions. A well-characterized model for the application of these emerging technologies is the development and differentiation of the ocular lens and how individual pathways regulate lens morphogenesis, gene expression, transparency, and refraction. Recent applications of next-generation sequencing analysis on well-characterized chicken and mouse lens differentiation models using a variety of omics techniques including RNA-seq, ATAC-seq, whole-genome bisulfite sequencing (WGBS), chip-seq, and CUT&RUN have revealed a wide range of essential biological pathways and chromatin features governing lens structure and function. Multiomics integration of these data has established new gene functions and cellular processes essential for lens formation, homeostasis, and transparency including the identification of novel transcription control pathways, autophagy remodeling pathways, and signal transduction pathways, among others. This review summarizes recent omics technologies applied to the lens, methods for integrating multiomics data, and how these recent technologies have advanced our understanding ocular biology and function. The approach and analysis are relevant to identifying the features and functional requirements of more complex tissues and disease states.

Corneal transplantation in aniridia-related keratopathy with a two-year follow-up period, an uncommon disease with precarious course

PURPOSE

The purpose of this study is to study the frequency, surgical transplantation technique and outcome in patients with aniridia-related keratopathy (ARK) with two-year follow-up period.

METHODS

A retrospective registry-study including all ARK cases performed in Sweden and Denmark between 2001 and 2016 and registered in the Swedish Cornea Transplant Registry.

RESULTS

A total of 36 eyes of 26 patients were subjected to corneal transplantation due to ARK during 2001 to 2016. Penetrating keratoplasty (PK) was the procedure of choice in 58.3% (n = 21) of the eyes, followed by a combination of PK and limbal stem cell transplantation in 13.9% (n = 5) and keratolimbal allograft in 13.9% (n = 5). Boston keratoprosthesis was used in 8.3% (n = 3), and anterior lamellar keratoplasty in 5.6% (n = 2). Thirteen of the procedures (36.1%) were retransplantations. Two years after surgery 26 cases were available to follow-up of which 16 of the grafts were functioning (61.5%). The median visual acuity showed a trend of improvement from hand motion to counting fingers.

CONCLUSIONS

A majority of the ARK cases (61.5%) had a graft providing useful vision for the patient 2 years after corneal transplantation, but the visual gain was modest at best. Longer follow-up time is required to evaluate functional graft outcomes. Despite the introduction of limbal stem cell transplantation as a suitable treatment, PK was the most common surgical method in the present study.

The Effects of Co-Culture of Embryonic Stem Cells with Neural Stem Cells on Differentiation

Researching the technology for in vitro differentiation of embryonic stem cells (ESCs) into neural lineages is very important in developmental biology, regenerative medicine, and cell therapy. Thus, studies on in vitro differentiation of ESCs into neural lineages by co-culture are expected to improve our understanding of this process. A co-culture system has long been used to study interactions between cell populations, improve culture efficiency, and establish synthetic interactions between populations. In this study, we investigated the effect of a co-culture of ESCs with neural stem cells (NSCs) in two-dimensional (2D) or three-dimensional (3D) culture conditions. Furthermore, we examined the effect of an NSC-derived conditioned medium (CM) on ESC differentiation. OG2-ESCs lost the specific morphology of colonies and Oct4-GFP when co-cultured with NSC. Additionally, real-time PCR analysis showed that ESCs co-cultured with NSCs expressed higher levels of ectoderm markers Pax6 and Sox1 under both co-culture conditions. However, the differentiation efficiency of CM was lower than that of the non-conditioned medium. Collectively, our results show that co-culture with NSCs promotes the differentiation of ESCs into the ectoderm.

Cell fate decisions, transcription factors and signaling during early retinal development

The development of the vertebrate eyes is a complex process starting from anterior-posterior and dorso-ventral patterning of the anterior neural tube, resulting in the formation of the eye field. Symmetrical separation of the eye field at the anterior neural plate is followed by two symmetrical evaginations to generate a pair of optic vesicles. Next, reciprocal invagination of the optic vesicles with surface ectoderm-derived lens placodes generates double-layered optic cups. The inner and outer layers of the optic cups develop into the neural retina and retinal pigment epithelium (RPE), respectively. In vitro produced retinal tissues, called retinal organoids, are formed from human pluripotent stem cells, mimicking major steps of retinal differentiation in vivo. This review article summarizes recent progress in our understanding of early eye development, focusing on the formation the eye field, optic vesicles, and early optic cups. Recent single-cell transcriptomic studies are integrated with classical in vivo genetic and functional studies to uncover a range of cellular mechanisms underlying early eye development. The functions of signal transduction pathways and lineage-specific DNA-binding transcription factors are dissected to explain cell-specific regulatory mechanisms underlying cell fate determination during early eye development. The functions of homeodomain (HD) transcription factors Otx2, Pax6, Lhx2, Six3 and Six6, which are required for early eye development, are discussed in detail. Comprehensive understanding of the mechanisms of early eye development provides insight into the molecular and cellular basis of developmental ocular anomalies, such as optic cup coloboma. Lastly, modeling human development and inherited retinal diseases using stem cell-derived retinal organoids generates opportunities to discover novel therapies for retinal diseases.

Porcn is essential for growth and invagination of the mammalian optic cup

Microphthalmia, anophthalmia, and coloboma (MAC) are congenital ocular malformations causing 25% of childhood blindness. The X-linked disorder Focal Dermal Hypoplasia (FDH) is frequently associated with MAC and results from mutations in Porcn, a membrane bound O-acyl transferase required for palmitoylation of Wnts to activate multiple Wnt-dependent pathways. Wnt/β-catenin signaling is suppressed in the anterior neural plate for initiation of eye formation and is subsequently required during differentiation of the retinal pigment epithelium (RPE). Non-canonical Wnts are critical for early eye formation in frog and zebrafish. However, it is unclear whether this also applies to mammals. We performed ubiquitous conditional inactivation of Porcn in mouse around the eye field stage. In Porcn CKO , optic vesicles (OV) arrest in growth and fail to form an optic cup. Ventral proliferation is significantly decreased in the mutant OV, with a concomitant increase in apoptotic cell death. While pan-ocular transcription factors such as PAX6, SIX3, LHX2, and PAX2 are present, indicative of maintenance of OV identity, regional expression of VSX2, MITF, OTX2, and NR2F2 is downregulated. Failure of RPE differentiation in Porcn CKO is consistent with downregulation of the Wnt/β-catenin effector LEF1, starting around 2.5 days after inactivation. This suggests that Porcn inactivation affects signaling later than a potential requirement for Wnts to promote eye field formation. Altogether, our data shows a novel requirement for Porcn in regulating growth and morphogenesis of the OV, likely by controlling proliferation and survival. In FDH patients with ocular manifestations, growth deficiency during early ocular morphogenesis may be the underlying cause for microphthalmia.

Nicotinamide improves in vitro lens regeneration in a mouse capsular bag model

Background

Mammalian lens regeneration holds great potential as a cataract therapy. However, the mechanism of mammalian lens regeneration is unclear, and the methods for optimization remain in question.

Methods

We developed an in vitro lens regeneration model using mouse capsular bag culture and improved the transparency of the regenerated lens using nicotinamide (NAM). We used D4476 and SSTC3 as a casein kinase 1A inhibitor and agonist, respectively. The expression of lens-specific markers was examined by real-time PCR, immunostaining, and western blotting. The structure of the in vitro regenerated lens was investigated using 3,3′-dihexyloxacarbocyanine iodide (DiOC6) and methylene blue staining, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and transmission electron microscopy.

Results

The in vitro lens regeneration model was developed to mimic the process of in vivo mammalian lens regeneration in a mouse capsular bag culture. In the early stage, the remanent lens epithelial cells proliferated across the posterior capsule and differentiated into lens fiber cells (LFCs). The regenerated lenses appeared opaque after 28 days; however, NAM treatment effectively maintained the transparency of the regenerated lens. We demonstrated that NAM maintained lens epithelial cell survival, promoted the differentiation and regular cellular arrangement of LFCs, and reduced lens-related cell apoptosis. Mechanistically, NAM enhanced the differentiation and transparency of regenerative lenses partly by inhibiting casein kinase 1A activity.

Conclusion

This study provides a new in vitro model for regeneration study and demonstrates the potential of NAM in in vitro mammalian lens regeneration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02862-8.

Mapping transgene insertion sites reveals the α-Cre transgene expression in both developing retina and olfactory neurons

The Tg(Pax6-cre,GFP)^2Pgr (α-Cre) mouse is a commonly used Cre line thought to be retinal-specific. Using targeted locus amplification (TLA), we mapped the insertion site of the transgene, and defined primers useful to deduce zygosity. Further analyses revealed four tandem copies of the transgene. The insertion site mapped to clusters of vomeronasal and olfactory receptor genes. Using R26R and Ai14 Cre reporter mice, we confirmed retinal Cre activity, but also detected expression in Gα₀⁺ olfactory neurons. Most α-Cre⁺ olfactory neurons do not express Pax6, implicating the influence of neighboring regulatory elements. RT-PCR and buried food pellet test did not detect any effects of the transgene on flanking genes in the nasal mucosa and retina. Together, these data precisely map α-Cre, show that it does not affect surrounding loci, but reveal previously unanticipated transgene expression in olfactory neurons. The α-Cre mouse can be a valuable tool in both retinal and olfactory research.

The Pax6-α-Cre mouse line used in retinal studies actually contains four transgene insertion within gene clusters of olfactory and vomeronasal receptors, leading to expression in not just retinal, but also olfactory and vomeronasal sensory neurons.

Pathophysiology of aniridia-associated keratopathy: Developmental aspects and unanswered questions

Aniridia, a rare congenital disease, is often characterized by a progressive, pronounced limbal insufficiency and ocular surface pathology termed aniridia-associated keratopathy (AAK). Due to the characteristics of AAK and its bilateral nature, clinical management is challenging and complicated by the multiple coexisting ocular and systemic morbidities in aniridia. Although it is primarily assumed that AAK originates from a congenital limbal stem cell deficiency, in recent years AAK and its pathogenesis has been questioned in the light of new evidence and a refined understanding of ocular development and the biology of limbal stem cells (LSCs) and their niche. Here, by consolidating and comparing the latest clinical and preclinical evidence, we discuss key unanswered questions regarding ocular developmental aspects crucial to AAK. We also highlight hypotheses on the potential role of LSCs and the ocular surface microenvironment in AAK. The insights thus gained lead to a greater appreciation for the role of developmental and cellular processes in the emergence of AAK. They also highlight areas for future research to enable a deeper understanding of aniridia, and thereby the potential to develop new treatments for this rare but blinding ocular surface disease.

The rax homeobox gene is mutated in the eyeless axolotl, Ambystoma mexicanum

BACKGROUND

Vertebrate eye formation requires coordinated inductive interactions between different embryonic tissue layers, first described in amphibians. A network of transcription factors and signaling molecules controls these steps, with mutations causing severe ocular, neuronal, and craniofacial defects. In eyeless mutant axolotls, eye morphogenesis arrests at the optic vesicle stage, before lens induction, and development of ventral forebrain structures is disrupted.

RESULTS

We identified a 5-bp deletion in the rax (retina and anterior neural fold homeobox) gene, which was tightly linked to the recessive eyeless (e) axolotl locus in an F2 cross. This frameshift mutation, in exon 2, truncates RAX protein within the homeodomain (P154fs35X). Quantitative RNA analysis shows that mutant and wild-type rax transcripts are equally abundant in E/e embryos. Translation appears to initiate from dual start codons, via leaky ribosome scanning, a conserved feature among gnathostome RAX proteins. Previous data show rax is expressed in the optic vesicle and diencephalon, deeply conserved among metazoans, and required for eye formation in other species.

CONCLUSION

The eyeless axolotl mutation is a null allele in the rax homeobox gene, with primary defects in neural ectoderm, including the retinal and hypothalamic primordia.

The retinal pigment epithelium: Development, injury responses, and regenerative potential in mammalian and non-mammalian systems

Diseases that result in retinal pigment epithelium (RPE) degeneration, such as age-related macular degeneration (AMD), are among the leading causes of blindness worldwide. Atrophic (dry) AMD is the most prevalent form of AMD and there are currently no effective therapies to prevent RPE cell death or restore RPE cells lost from AMD. An intriguing approach to treat AMD and other RPE degenerative diseases is to develop therapies focused on stimulating endogenous RPE regeneration. For this to become feasible, a deeper understanding of the mechanisms underlying RPE development, injury responses and regenerative potential is needed. In mammals, RPE regeneration is extremely limited; small lesions can be repaired by the expansion of adjacent RPE cells, but large lesions cannot be repaired as remaining RPE cells are unable to functionally replace lost RPE tissue. In some injury paradigms, RPE cells proliferate but do not regenerate a morphologically normal monolayer, while in others, proliferation is pathogenic and results in further disruption to the retina. This is in contrast to non-mammalian vertebrates, which possess tremendous RPE regenerative potential. Here, we discuss what is known about RPE formation during development in mammalian and non-mammalian vertebrates, we detail the processes by which RPE cells respond to injury, and we describe examples of RPE-to-retina and RPE-to-RPE regeneration in non-mammalian vertebrates. Finally, we outline barriers to RPE-dependent regeneration in mammals that could potentially be overcome to stimulate a regenerative response from the RPE.

Mechanisms underlying pre- and postnatal development of the vomeronasal organ

The vomeronasal organ (VNO) is sensory organ located in the ventral region of the nasal cavity in rodents. The VNO develops from the olfactory placode during the secondary invagination of olfactory pit. The embryonic vomeronasal structure appears as a neurogenic area where migratory neuronal populations like endocrine gonadotropin-releasing hormone-1 (GnRH-1) neurons form. Even though embryonic vomeronasal structures are conserved across most vertebrate species, many species including humans do not have a functional VNO after birth. The vomeronasal epithelium (VNE) of rodents is composed of two major types of vomeronasal sensory neurons (VSNs): (1) VSNs distributed in the apical VNE regions that express vomeronasal type-1 receptors (V1Rs) and the G protein subunit Gαi2, and (2) VSNs in the basal territories of the VNE that express vomeronasal type-2 receptors (V2Rs) and the G subunit Gαo. Recent studies identified a third subclass of Gαi2 and Gαo VSNs that express the formyl peptide receptor family. VSNs expressing V1Rs or V2Rs send their axons to distinct regions of the accessory olfactory bulb (AOB). Together, VNO and AOB form the accessory olfactory system (AOS), an olfactory subsystem that coordinates the social and sexual behaviors of many vertebrate species. In this review, we summarize our current understanding of cellular and molecular mechanisms that underlie VNO development. We also discuss open questions for study, which we suggest will further enhance our understanding of VNO morphogenesis at embryonic and postnatal stages.

Structural and functional consequences of PAX6 mutations in the brain: Implications for aniridia

The paired-box 6 (PAX6) gene encodes a highly conserved transcription factor essential for the proper development of the eye and brain. Heterozygous loss-of-function mutations in PAX6 are causal for a condition known as aniridia in humans and the Small eye phenotype in mice. Aniridia is characterized by iris hypoplasia and other ocular abnormalities, but recent evidence of neuroanatomical, sensory, and cognitive impairments in this population has emerged, indicating brain-related phenotypes as a prevalent feature of the disorder. Determining the neurophysiological origins of brain-related phenotypes in this disorder presents a substantial challenge, as the majority of extra-ocular traits in aniridia demonstrate a high degree of heterogeneity. Here, we summarize and integrate findings from human and rodent model studies, which have focused on neuroanatomical and functional consequences of PAX6 mutations. We highlight novel findings from PAX6 central nervous system studies in adult mammals, and integrate these findings into what we know about PAX6's role in development of the central nervous system. This review presents the current literature in the field in order to inform clinical application, discusses what is needed in future studies, and highlights PAX6 as a lens through which to understand genetic disorders affecting the human nervous system.

Usefulness of PAX8 Immunohistochemistry in Adult Intraocular Tumor Diagnosis

PURPOSE

To evaluate the distribution of the PAX8 transcription factor protein in ocular tissues and to investigate if immunohistochemical stains for this biomarker are useful in the diagnosis of intraocular tumors.

DESIGN

Observational case series.

PARTICIPANTS

Excision and cytologic analysis specimens of 6 ciliary body epithelial neoplasms, 2 iris epithelial neoplasms, 3 retinal pigment epithelial neoplasms, 3 intraocular medulloepitheliomas, 15 uveal melanomas, and 5 uveal melanocytomas.

METHODS

Hematoxylin-eosin and PAX8 immunohistochemical stains were performed on all specimens. In appropriate cases, bleached preparations and other immunohistochemical stains, including AE1/AE3 cytokeratin, Lin28A, and CD45, were performed.

MAIN OUTCOME MEASURES

Distribution of PAX8 expression in normal and neoplastic tissue.

RESULTS

Strong nuclear PAX8 expression was observed in the normal corneal epithelium, iris sphincter pupillae muscle, iris pigment epithelium and dilator muscle complex, nonpigmented and pigmented epithelia of the ciliary body, lens epithelium, and a subset of retinal neurons. The normal retinal pigment epithelium and uveal melanocytes did not stain for PAX8. The ciliary body epithelial and neuroepithelial tumors (adenoma, adenocarcinoma, and medulloepithelioma) showed uniform strong nuclear PAX8 immunoreactivity. All melanocytic tumors (iris melanoma, ciliary-choroidal melanoma, and melanocytoma) and retinal pigment epithelial neoplasms showed negative results for PAX8. A subset of tumor-associated lymphocytes, most prominent in uveal melanoma, showed positive results for PAX8. The uniformity of the PAX8 staining was superior to the variable cytokeratin staining in the ciliary epithelial neoplasms and the variable Lin28A staining in malignant medulloepithelioma. The veracity of PAX8 staining was equally as robust on cytologic analysis and open-flap biopsy specimens of ciliary epithelial and iris epithelial neoplasms, melanocytoma, and melanoma.

CONCLUSIONS

PAX8 has proven to be a very useful diagnostic marker in a select group of adult intraocular tumors, and we highly recommend its inclusion in diagnostic antibody panels of morphologically challenging intraocular neoplasms.

Phenotype Variability in Czech Patients Carrying PAX6 Disease-Causing Variants

The aim of this study was to report PAX6 disease-causing variants in six Czech families, to describe the associated phenotypes, and to perform functional assessment of the splice site variants. Detailed ophthalmic examination was performed. The PAX6 coding region was directly sequenced in three probands. Two probands were analysed by exome sequencing and one by genome sequencing. The effect of two variants on pre-mRNA splicing was evaluated using an exon trapping assay. Six different heterozygous PAX6 variants were identified, with c.111_120del and c.1183+1G˃T being novel. Both c.1183+1G˃T and c.1032+1G>A were proved to cause aberrant splicing with exon skipping and subsequent frameshift. The phenotypic features were variable between and within families. One individual, aged 31 years, presented with mild unilateral ptosis accompanied by aniridia in the right eye, partial aniridia in the left eye, and bilateral congenital cataracts, without marked foveal hypoplasia. Bilateral microcornea, partial aniridia, congenital cataracts, and a large posterior segment coloboma were found in another proband, aged 32 years. One child, aged 8 years, had bilateral high myopia, optic nerve colobomas, anterior polar cataracts, but no iris defects. Another individual, aged 46 years, had bilateral congenital ptosis, iris hypoplasia, keratopathy with marked fibrovascular pannus, anterior polar cataract, and foveal hypoplasia combined with impaired glucose tolerance. However, his daughter, aged 11 years, showed classical features of aniridia. Our study extends the genetic spectrum of PAX6 disease-causing variants and confirms that the associated phenotypic features may be very broad and different to the 'classical' aniridia.

The Molecular Basis of Human Anophthalmia and Microphthalmia

Human eye development is coordinated through an extensive network of genetic signalling pathways. Disruption of key regulatory genes in the early stages of eye development can result in aborted eye formation, resulting in an absent eye (anophthalmia) or a small underdeveloped eye (microphthalmia) phenotype. Anophthalmia and microphthalmia (AM) are part of the same clinical spectrum and have high genetic heterogeneity, with >90 identified associated genes. By understanding the roles of these genes in development, including their temporal expression, the phenotypic variation associated with AM can be better understood, improving diagnosis and management. This review describes the genetic and structural basis of eye development, focusing on the function of key genes known to be associated with AM. In addition, we highlight some promising avenues of research involving multiomic approaches and disease modelling with induced pluripotent stem cell (iPSC) technology, which will aid in developing novel therapies.

Structural and functional defects of the respiratory neural system in the medulla and spinal cord of Pax6 mutant rats

Pax6 is an important transcription factor expressed in several discrete domains of the developing central nervous system. It has been reported that Pax6 is involved in the specification of subtypes of hindbrain motor neurons. Pax6 homozygous mutant (rSey²/rSey²) rats die soon after birth, probably due to impaired respiratory movement. To determine whether the respiratory center in the medulla functions normally, we analyzed the histological and neurophysiological properties of the medulla and spinal cord in fetal rats with this mutation. First, the medulla of rSey²/rSey² at embryonic (E) 21.5-E22.5 tended to be smaller than those from heterozygous mutant (rSey²/+) and wild-type (+/+) littermates. Through immunohistochemical analysis, we confirmed normal distribution of Phox2b-expressing cells in the parafacial respiratory group (pFRG) of rSey²/rSey² rats. Expression of neurokinin-1 receptor (NK-1R) was weak and dispersed in rSey²/rSey² rats. In addition, rSey²/rSey² rats have a defect of the hypoglossal nerve root. Electrophysiological analysis using brainstem-spinal cord preparations (E21.5-E22.5) revealed that rSey²/rSey² rats showed larger fluctuation of the amplitude of inspiratory activity monitored from the fourth cervical root although there was no significant difference in the respiratory rate among rSey²/rSey², rSey²/+, and +/+ littermates. The response of respiratory rhythm to high CO₂ was similar among all genotypes. Optical recordings of neuronal activity revealed that the activity of the pFRG tended to be weaker and inspiratory activity appeared in more scattered areas in the caudal ventral medulla in the rSey²/rSey² rats. These results suggest that the basal activity of the respiratory system was preserved with mild impairment of the inspiratory activity in the rSey²/rSey² rats and that the Pax6 gene is involved in the functional development of the neuronal system producing effective inspiratory motor outputs for survival.

Pax 6 Controls Neural Crest Potential of Limbal Niche Cells to Support Self-Renewal of Limbal Epithelial Stem Cells

On ocular surface, corneal epithelial stem cells (SC) reside in limbus between cornea and conjunctiva. Pax6, an evolutionally conserved transcription factor essential for eye development, is expressed in post-natal corneal and limbal epithelia progenitors (LEPC) but not in underlying stroma. Because Pax6 is transiently expressed in developing corneal stroma and a subset of limbal and corneal stromal progenitors, we examined the role of Pax6 in limbal niche cells (LNC) in maintaining the phenotype of neural crest (NC) progenitors to support LEPC. Our results showed that nuclear Pax6 staining was found in freshly isolated LNC but not corneal stromal cells. Serial passaged LNC resulted in gradual loss of nuclear Pax6 (46 kDa) staining and neural crest progenitor status defined by the expression of embryonic SCs and NC markers, neurosphere formation, and differentiation into neurons, oligodendrocytes and astrocytes. Gain of function of 46 kDa Pax6 in late-passaged LNC resulted in nuclear Pax6 staining and promotion of the aforementioned NC progenitor status. In an in vitro reunion assay, early passaged LNC and late passaged LNC with overexpression of Pax6 inhibited the expression of corneal epithelial differentiation marker and promoted holoclone by LEPC. Therefore, expression of nuclear 46 kDa Pax6 in LNC plays an important developmental role in maintaining NC progenitor status to support self-renewal of corneal epithelial SCs in the limbal niche.

The molecular anatomy of mammalian upper lip and primary palate fusion at single cell resolution

The mammalian lip and primary palate form when coordinated growth and morphogenesis bring the nasal and maxillary processes into contact, and the epithelia co-mingle, remodel and clear from the fusion site to allow mesenchyme continuity. Although several genes required for fusion have been identified, an integrated molecular and cellular description of the overall process is lacking. Here, we employ single cell RNA sequencing of the developing mouse face to identify ectodermal, mesenchymal and endothelial populations associated with patterning and fusion of the facial prominences. This analysis indicates that key cell populations at the fusion site exist within the periderm, basal epithelial cells and adjacent mesenchyme. We describe the expression profiles that make each population unique, and the signals that potentially integrate their behaviour. Overall, these data provide a comprehensive high-resolution description of the various cell populations participating in fusion of the lip and primary palate, as well as formation of the nasolacrimal groove, and they furnish a powerful resource for those investigating the molecular genetics of facial development and facial clefting that can be mined for crucial mechanistic information concerning this prevalent human birth defect.

MicroRNA-655-3p and microRNA-497-5p inhibit cell proliferation in cultured human lip cells through the regulation of genes related to human cleft lip

Background

The etiology of cleft lip with or without cleft palate (CL/P), a common congenital birth defect, is complex and involves the contribution of genetic and environmental factors. Although many candidate genes have been identified, the regulation and interaction of these genes in CL/P remain unclear. In addition, the contribution of microRNAs (miRNAs), non-coding RNAs that regulate the expression of multiple genes, to the etiology of CL/P is largely unknown.

Methods

To identify the signatures of causative biological pathways for human CL/P, we conducted a systematic literature review for human CL/P candidate genes and subsequent bioinformatics analyses. Functional enrichment analyses of the candidate CL/P genes were conducted using the pathway databases GO and KEGG. The miRNA-mediated post-transcriptional regulation of the CL/P candidate genes was analyzed with miRanda, PITA, and TargetScan, and miRTarbase. Genotype-phenotype association analysis was conducted using GWAS. The functional significance of the candidate miRNAs was evaluated experimentally in cell proliferation and target gene regulation assays in human lip fibroblasts.

Results

Through an extensive search of the main biomedical databases, we mined 177 genes with mutations or association/linkage reported in individuals with CL/P, and considered them as candidate genes for human CL/P. The genotype-phenotype association study revealed that mutations in 12 genes (ABCA4, ADAM3A, FOXE1, IRF6, MSX2, MTHFR, NTN1, PAX7, TP63, TPM1, VAX1, and WNT9B) were significantly associated with CL/P. In addition, our bioinformatics analysis predicted 16 microRNAs (miRNAs) to be post-transcriptional regulators of CL/P genes. To validate the bioinformatics results, the top six candidate miRNAs (miR-124-3p, miR-369-3p, miR-374a-5p, miR-374b-5p, miR-497-5p, and miR-655-3p) were evaluated by cell proliferation/survival assays and miRNA-gene regulation assays in cultured human lip fibroblasts. We found that miR-497-5p and miR-655-3p significantly suppressed cell proliferation in these cells. Furthermore, the expression of the predicted miRNA-target genes was significantly downregulated by either miR-497-5p or miR-655-3p mimic.

Conclusion

Expression of miR-497-5p and miR-655-3p suppresses cell proliferation through the regulation of human CL/P-candidate genes. This study provides insights into the role of miRNAs in the etiology of CL/P and suggests possible strategies for the diagnosis of CL/P.

Electronic supplementary material

The online version of this article (10.1186/s12920-019-0535-2) contains supplementary material, which is available to authorized users.

The strengths of the genetic approach to understanding neural systems development and function: Ray Guillery's synthesis

The organization and function of sensory systems, especially the mammalian visual system, has been the focus of philosophers and scientists for centuries-from Descartes and Newton onward. Nevertheless, the utility of understanding development and its genetic foundations for deeper insight into neural function has been debated: Do you need to know how something is assembled-a car, for example-to understand how it works or how to use it-to turn on the ignition and drive? This review addresses this issue for sensory pathways. The pioneering work of the late Rainer W. (Ray) Guillery provides an unequivocal answer to this central question: Using genetics for mechanistic exploration of sensory system development yields essential knowledge of organization and function. Ray truly built the foundation for this now accepted tenet of modern neuroscience. His work on the development and reorganization of visual pathways in albino mammals-all with primary genetic mutations in genes for pigmentation-defined the genetic approach to neural systems development, function and plasticity. The work that followed his lead in a variety of sensory systems, including my own work in the developing olfactory system, proceeds directly from Ray's fundamental contributions.

Mapping the Pax6 3' untranslated region microRNA regulatory landscape

BACKGROUND

PAX6 is a homeodomain transcription factor that acts in a highly dosage-sensitive manner to regulate the development and function of the eyes, nose, central nervous system, gut, and endocrine pancreas. Several individual microRNAs (miRNA) have been implicated in regulating PAX6 in different cellular contexts, but a more general view of how they contribute to the fine-tuning and homeostasis of PAX6 is poorly understood.

RESULTS

Here, a comprehensive analysis of the Pax6 3' untranslated region was performed to map potential miRNA recognition elements and served as a backdrop for miRNA expression profiling experiments to identify potential cell/tissue-specific miRNA codes. Pax6 3'UTR pull-down studies identified a cohort of miRNA interactors in pancreatic αTC1-6 cells that, based on the spacing of their recognition sites in the Pax6 3'UTR, revealed 3 clusters where cooperative miRNA regulation may occur. Some of these interacting miRNAs have been implicated in α cell function but have not previously been linked to Pax6 function and may therefore represent novel PAX6 regulators.

CONCLUSIONS

These findings reveal a regulatory landscape upon which miRNAs may participate in the developmental control, fine-tuning and/or homeostasis of PAX6 levels.

A conditional Pax6 depletion study with no morphological effect on the adult mouse corneal epithelium

OBJECTIVE

The corneas of heterozygous Pax6+/- mice develop abnormally and deteriorate further after birth but it is not known whether the postnatal deterioration is predetermined by abnormal development. Our objective was to identify whether depletion of Pax6 in adult mice caused any corneal abnormalities, similar to those in Pax6+/- mice, where Pax6 levels are low throughout development and adulthood. We used two tamoxifen-inducible, Cre-loxP experimental strategies to deplete Pax6 either ubiquitously or in a restricted range of cell types.

RESULTS

In a preliminary study, ubiquitous depletion of Pax6 by tamoxifen treatment of E9.5 CAG-CreERTg/-;Pax6fl/fl embryos affected eye development. Tamoxifen treatment of 12-week old, adult CAG-CreERTg/-;Pax6fl/+ and CAG-CreERTg/-;Pax6fl/fl mice resulted in weak and/or patchy Pax6 immunostaining in the corneal epithelium but caused no corneal abnormalities. GFP staining in tamoxifen-treated CAG-CreERTg/-;RCE:loxP reporter mice was also patchy. We attribute patchy Pax6 staining to mosaic deletion of the Pax6fl allele, probably caused by mosaic CAG-CreERTg expression. In a parallel study, we treated adult Krt19-CreERTg/-;Pax6fl/+ mice with tamoxifen to try to deplete Pax6 in limbal epithelial stem cells (LESCs) which replenish the corneal epithelium. However, Pax6 staining remained strong after a 12-week chase period so the Krt19-CreERTg/- transgene may have failed to target LESCs.

Epistasis between Pax6Sey and genetic background reinforces the value of defined hybrid mouse models for therapeutic trials

The small eye (Sey) mouse is a model of PAX6-aniridia syndrome (aniridia). Aniridia, a congenital ocular disorder caused by heterozygous loss-of-function mutations in PAX6, needs new vision saving therapies. However, high phenotypic variability in Sey mice makes development of such therapies challenging. We hypothesize that genetic background is a major source of undesirable variability in Sey mice. Here we performed a systematic quantitative examination of anatomical, histological, and molecular phenotypes on the inbred C57BL/6J, hybrid B6129F1, and inbred 129S1/SvImJ backgrounds. The Sey allele significantly reduced eye weight, corneal thickness, PAX6 mRNA and protein levels, and elevated blood glucose levels. Surprisingly, Pax6^Sey/Sey brains had significantly elevated Pax6 transcripts compared to Pax6^+/+ embryos. Genetic background significantly influenced 12/24 measurements, with inbred strains introducing severe ocular and blood sugar phenotypes not observed in hybrid mice. Additionally, significant interactions (epistasis) between Pax6 genotype and genetic background were detected in measurements of eye weight, cornea epithelial thickness and cell count, retinal mRNA levels, and blood glucose levels. The number of epistatic interactions was reduced in hybrid mice. In conclusion, severe phenotypes in the unnatural inbred strains reinforce the value of more naturalistic F1 hybrid mice for the development of therapies for aniridia and other disorders.

Molecular regulation of ocular gland development

The tear film is produced by two ocular glands, the lacrimal glands, which produce the aqueous component of this film, and the meibomian glands, which secrete the lipidic component that is key to reduce evaporation of the watery film at the surface of the eye. Embryonic development of these exocrine glands has been mostly studied in mice, which also develop Harderian glands, a third type of ocular gland whose role is still not well understood. This review provides an update on the signalling pathways, transcription factors andextracellular matrix components that have been shown to play a role in ocular gland development.

Ndr kinases regulate retinal interneuron proliferation and homeostasis

Ndr2/Stk38l encodes a protein kinase associated with the Hippo tumor suppressor pathway and is mutated in a naturally-occurring canine early retinal degeneration (erd). To elucidate the retinal functions of Ndr2 and its paralog Ndr1/Stk38, we generated Ndr1 and Ndr2 single knockout mice. Although retinal lamination appeared normal in these mice, Ndr deletion caused a subset of Pax6-positive amacrine cells to proliferate in differentiated retinas, while concurrently decreasing the number of GABAergic, HuD and Pax6-positive amacrine cells. Retinal transcriptome analyses revealed that Ndr2 deletion increased expression of neuronal stress genes and decreased expression of synaptic organization genes. Consistent with the latter, Ndr deletion dramatically reduced levels of Aak1, an Ndr substrate that regulates vesicle trafficking. Our findings indicate that Ndr kinases are important regulators of amacrine and photoreceptor cells and suggest that Ndr kinases inhibit the proliferation of a subset of terminally differentiated cells and modulate interneuron synapse function via Aak1.

i-GONAD (improved genome-editing via oviductal nucleic acids delivery), a convenient in vivo tool to produce genome-edited rats

Zygote-microinjection or in vitro electroporation of isolated zygotes are now widely used methods to produce genome-edited mice. However, these technologies require laborious and time-consuming ex vivo handling of fertilized eggs, including zygote isolation, gene delivery into zygotes and embryo transfer into recipients. We recently developed an alternative method called improved genome-editing via oviductal nucleic acids delivery (i-GONAD), which does not require the above-mentioned ex vivo handing of zygotes, but instead involves intraoviductal instillation of genome-editing components, Cas9 protein and synthetic gRNAs, into the oviducts of pregnant females at the late 1-cell embryo stage under a dissecting microscope and subsequent electroporation. With this method, we succeeded in generating genome-edited mice at relatively high efficiencies (for example, knockout alleles were produced at ~97% efficiency). Here, we extended this improved technology to rats, and found that i-GONAD can create genome-edited rats in various strains, including Sprague Dawley and Lewis, and F1 hybrids (between Sprague Dawley and Brown Norway), with efficiencies of ~62% for indel mutations and ~9% for knock-ins. Thus, i-GONAD will be especially useful for the production of genome-edited rats in small laboratories where expensive micromanipulator systems and highly skilled personnel for embryo manipulation are unavailable.

RNA-binding protein Rbpms is represented in human retinas by isoforms A and C and its transcriptional regulation involves Sp1-binding site

Rbpms (RNA-binding protein with multiple splicing) is a member of the RRM (RNA Recognition Motif) family of RNA-binding proteins, which is expressed as multiple alternatively spliced transcripts encoding different protein isoforms. We have shown earlier that Rbpms expression in the retina is restricted to retinal ganglion cells (RGCs), and have characterized this gene as a marker for RGCs. The aim of this study was to identify isoforms representing Rbpms in human retinas and to analyze its transcriptional regulation. We found that Rbpms is expressed as transcription variants 1 and 3 encoding isoforms A and C, respectively. These isoforms are encoded by the same first 6 exons but have different C-terminal ends encoded by exon 8 in variant 1 and exon 7 in variant 3. Computational analysis of the Rbpms 5' untranslated and flanking regions reveals the presence of three CpG islands and four predicted promoter regions (PPRs). The effect of PPR 1 (- 1672/- 1420) and PPR2 (- 330/- 79) on transcriptional activation was minimal, whereas PPR 3 (- 73/+ 177) and PPR4 (+ 274/+ 524) induced the expression by ~ 7 and ninefold compared to control, respectively. The maximum activity, a 30-fold increase above the control level, was obtained from the construct containing both PPRs 3 and 4. Site-directed mutagenesis of several cis-elements within PPR3 and PPR4 including five for Sp1, one for AP1, and two for NF-kB showed that mutation of the first three and especially the first GC box resulted in a threefold downregulation of gene expression. AP1, NF-kB, and two downstream Sp1 sites had no significant effect on expression level. The possible involvement of the GC box 1 at position - 54 in transcriptional regulation of Rbpms was corroborated by EMSA, which showed formation of a DNA-protein complex in the presence of the oligonucleotide corresponding to this Sp1-binding site.

Modeling of Aniridia-Related Keratopathy by CRISPR/Cas9 Genome Editing of Human Limbal Epithelial Cells and Rescue by Recombinant PAX6 Protein

Heterozygous PAX6 gene mutations leading to haploinsufficiency are the main cause of congenital aniridia, a rare and progressive panocular disease characterized by reduced visual acuity. Up to 90% of patients suffer from aniridia-related keratopathy (ARK), caused by a combination of factors including limbal epithelial stem cell (LSC) deficiency, impaired healing response and abnormal differentiation of the corneal epithelium. It usually begins in the first decade of life, resulting in recurrent corneal erosions, sub-epithelial fibrosis, and corneal opacification. Unfortunately, there are currently no efficient treatments available for these patients and no in vitro model for this pathology. We used CRISPR/Cas9 technology to introduce into the PAX6 gene of LSCs a heterozygous nonsense mutation found in ARK patients. Nine clones carrying a p.E109X mutation on one allele were obtained with no off-target mutations. Compared with the parental LSCs, heterozygous mutant LSCs displayed reduced expression of PAX6 and marked slow-down of cell proliferation, migration and detachment. Moreover, addition to the culture medium of recombinant PAX6 protein fused to a cell penetrating peptide was able to activate the endogenous PAX6 gene and to rescue phenotypic defects of mutant LSCs, suggesting that administration of such recombinant PAX6 protein could be a promising therapeutic approach for aniridia-related keratopathy. More generally, our results demonstrate that introduction of disease mutations into LSCs by CRISPR/Cas9 genome editing allows the creation of relevant cellular models of ocular disease that should greatly facilitate screening of novel therapeutic approaches. Stem Cells 2018;36:1421-1429.

Level of hydrogen peroxide affects expression and sub-cellular localization of Pax6

The Pax6 is a multifunctional pairedbox and homeobox containing transcription factor which is involved in several functions of brain, eyes, and pancreas. It regulates expression of genes involved in cell proliferation, differentiation, inflammation, oxidative stress management, and neuropathy. Dynamic changes in the sub-cellular localization of Pax6 are proposed to regulate its activity, however, the underlying mechanism remains poorly understood. The oxidative stress mediated changes were studied in sub-cellular localization of Pax6 in cultured cells derived from the eye (cornea) and pancreas. The impact of induced oxidative stress was investigated on reactive oxygen species scavenger molecules, Superoxide dismutase1 (SOD1) and Catalase, and a critical cell signalling molecule Transforming growth factor-beta (TGF-β1). The cells were treated with three different concentrations of H₂O_2, viz., 0.3, 1.5, and 3.0 mM. The cell viability was analysed through Trypan blue dye exclusion assay. The localization of Pax6 was observed by immunofluorescence labeling, and alterations in levels of Pax6, SOD1, Catalase, and TGF-β1 were investigated by semi-quantitative RT-PCR. Nucleo-cytoplasmic shuttling of Pax6 was observed in cells of corneal epithelial (SIRC) and pancreatic origins (MIA-PaCa2). The percentage distribution of Pax6 in nuclear and cytoplasmic compartments of SIRC and MIA-PaCa2 cells was analyzed through ImageJ software. Level of hydrogen peroxide affects expression and sub-cellular localization of Pax6. Expression of Pax6 and TGF-β1 are directly associated with changes in sub-cellular localization of Pax6 and modulation in expression of Catalase. This may be the result of a cellular protective mechanism against peroxide-dependent cellular stress.

Phenotypic Variation in a Four-Generation Family with Aniridia Carrying a Novel PAX6 Mutation

Aniridia is a congenital disease that affects almost all eye structures and is primarily caused by loss-of-function mutations in the PAX6 gene. The degree of vision loss in aniridia varies and is dependent on the extent of foveal, iris, and optic nerve hypoplasia and the presence of glaucoma, cataracts, and corneal opacification. Here, we describe a 4-generation family in which 7 individuals across 2 generations carry a novel disease-causing frameshift mutation (NM_000280.4(PAX6):c.565TC>T) in PAX6. This mutation results in an early stop codon in exon 8, which is predicted to cause nonsense-mediated decay of the truncated mRNA and a functionally null PAX6 allele. Family members with aniridia showed differences in multiple eye phenotypes including iris and optic nerve hypoplasia, congenital and acquired corneal opacification, glaucoma, and strabismus. Visual acuity ranged from 20/100 to less than 20/800. Patients who required surgical intervention for glaucoma or corneal opacification had worse visual outcomes. Our results show that family members carrying a novel PAX6 frameshift mutation have variable expressivity, leading to different ocular comorbidities and visual outcomes.