The expanding roles of Nr6a1 in development and evolution

The Nuclear Receptor (NR) family of transcriptional regulators possess the ability to sense signalling molecules and directly couple that to a transcriptional response. While this large class of proteins are united by sequence and structural homology, individual NR functional output varies greatly depending on their expression, ligand selectivity and DNA binding sequence specificity. Many NRs have remained somewhat enigmatic, with the absence of a defined ligand categorising them as orphan nuclear receptors. One example is Nuclear Receptor subfamily 6 group A member 1 (Nr6a1), an orphan nuclear receptor that has no close evolutionary homologs and thus is alone in subfamily 6. Nonetheless, Nr6a1 has emerged as an important player in the regulation of key pluripotency and developmental genes, as functionally critical for mid-gestational developmental progression and as a possible molecular target for driving evolutionary change in animal body plan. Here, we review the current knowledge on this enigmatic nuclear receptor and how it impacts development and evolution.

TBXT dose sensitivity and the decoupling of nascent mesoderm specification from EMT progression in 2D human gastruloids

In the nascent mesoderm, levels of Brachyury (TBXT) expression must be precisely regulated to ensure cells exit the primitive streak and pattern the anterior-posterior axis, but how this varying dosage informs morphogenesis is not well understood. In this study, we define the transcriptional consequences of TBXT dose reduction during early human gastrulation using human induced pluripotent stem cell (hiPSC)-based models of gastrulation and mesoderm differentiation. Multiomic single-nucleus RNA and single-nucleus ATAC sequencing of 2D gastruloids comprised of WT, TBXT heterozygous (TBXT-Het), or TBXT null (TBXT-KO) hiPSCs reveal that varying TBXT dosage does not compromise a cell's ability to differentiate into nascent mesoderm, but that the loss of TBXT significantly delays the temporal progression of the epithelial to mesenchymal transition (EMT). This delay is dependent on TBXT dose, as cells heterozygous for TBXT proceed with EMT at an intermediate pace relative to WT or TBXT-KO. By differentiating iPSCs of the allelic series into nascent mesoderm in a monolayer format, we further illustrate that TBXT dose directly impacts the persistence of junctional proteins and cell-cell adhesions. These results demonstrate that EMT progression can be decoupled from the acquisition of mesodermal identity in the early gastrula and shed light on the mechanisms underlying human embryogenesis.

Variation of Orthokeratology Lens Treatment Zone (VOLTZ) Study: A 2-year randomised clinical trial

PURPOSE

To compare axial elongation (AE) and treatment zone (TZ) characteristics in children wearing 6 mm or 5 mm back optic zone diameter (BOZD) orthokeratology (ortho-k) lenses over 2 years.

METHODS

Forty-five (6 to <11 years of age) myopic (-4.00 to -0.75 D) children of Chinese ethnicity were randomly assigned to use the two different lens designs (23 and 22 wore the 6 and 5 mm lenses, respectively). Data collection was performed at baseline and every 6-months after commencing lens wear.

RESULTS

After 24 months, subjects wearing lenses with a 5 mm BOZD achieved smaller TZ diameter (horizontal: 2.69 ± 0.28 vs. 3.84 ± 0.39 mm; vertical: 2.65 ± 0.22 vs. 3.42 ± 0.34 mm, p < 0.001) and less AE (0.15 ± 0.21 vs. 0.35 ± 0.23, p = 0.005) compared to those using the 6 mm design, with no difference in choroidal thickness (ChT) changes (p = 0.93). A significant increase in ChT, using pooled data analysis, was noted at the 6-month (11.8 ± 19.77 μm, p < 0.001) and 12-month (12.0 ± 23.7 μm, p = 0.004) visits, compared to baseline, indicating a transient change in ChT. Significant associations were noted, using linear mixed models, between AE and the TZ diameters (p < 0.003) after adjusting for baseline data. A very weak association was found between ChT changes and AE, with the effect size close to zero.

CONCLUSIONS

Smaller BOZD ortho-k lenses resulted in a smaller TZ diameter, which was associated with less AE after 2 years of treatment. The changes in ChT played a very weak role, suggesting that other factors may contribute more to the reduced AE in subjects wearing lenses having a smaller BOZD.

One-year results for myopia control with aspheric base curve orthokeratology lenses: A prospective randomised clinical trial

PURPOSE

To compare the effect of orthokeratology (ortho-k) using aspheric or spherical base curve (BCA vs. BCS) contact lenses on axial elongation and the relative peripheral refraction change (RPRC) in Chinese children.

METHODS

Children aged 8-12 years with myopia between -0.75 and -4.00 D and astigmatism ≤1.00 D were randomly assigned to the BCA or BCS group. Peripheral refraction was assessed at 10°, 20° and 30° along the temporal and nasal retina at baseline and at the 12-month visit. Axial length (AL) was measured under cycloplegia at baseline and at the 6- and 12-month visits. Only right eye data were analysed. Repeated-measures analysis of covariance was performed to examine the differences in axial elongation and the RPRC between the BCA and BCS groups.

RESULTS

The 1-year results from 31 BCA and 32 BCS subjects were analysed. No significant between-group differences were found at baseline (p ≥ 0.28). At the 12-month visit, the BCA lens produced a greater absolute RPRC along the horizontal meridian than the BCS lens (p < 0.001). Axial elongation was slower in the BCA group (0.19 ± 0.20 mm) than in the BCS group (0.29 ± 0.14 mm; p = 0.03). Axial elongation was correlated with the RPRC at 10° (r = 0.43, p = 0.02) and 20° (r = 0.39, p = 0.03) along the temporal retina in the BCA group; however, these correlations were not observed in the BCS group.

CONCLUSION

The BCA ortho-k lens could improve the efficacy of slowing axial elongation in children. The improved myopia control observed in the BCA group may be the result of a larger myopic shift in relative peripheral refraction within 20° along the temporal retina.

Reduction of experimental ocular axial elongation by neuregulin-1 antibody

Background

Since the mechanisms underlying myopic axial elongation have remained unclear, we examined the effect of neuregulin-1 (NRG-1), an epidermal growth factor family member, on myopic axial elongation.

Methods

The guinea pigs aged two to three weeks were subjected to bilateral negative lens-induced axial elongation and received weekly intravitreal injections into their right eyes of NRG-1 antibody (doses: 5 μg, n = 8; 10 μg, n = 8, 20 μg, n = 9) or of NRG-1 (doses: 0.05 μg, n = 8; 0.01 μg, n = 9; 0.2 μg, n = 8), underwent only bilateral negative lens-induced axial elongation (myopia control group, n = 10), or underwent no intervention (control group, n = 10). The contralateral eyes received corresponding intravitreal phosphate-buffered solution injections. One week after the last injection, the guinea pigs were sacrificed, the eyeballs were removed, the thicknesses of the retina and sclera were histologically examined, the expression of NRG-1 and downstream signal transduction pathway members (ERK1/2 and PI3K/AKT) and the mRNA expression of NRG-1 in the retina was assessed.

Results

The inter-eye difference in axial length at study end increased (p < 0.001) from the normal control group (-0.02 ± 0.09 mm) and the myopia control group (-0.01 ± 0.09 mm) to the low-dose NRG-1 antibody group (-0.11 ± 0.05 mm), medium-dose NRG-1 antibody group (-0.17 ± 0.07 mm), and high-dose NRG-1 antibody group (-0.28 ± 0.06 mm). The relative expression of NRG-1, ERK1/2, and PI3K/AKT in the retina decreased in a dose-dependent manner from the myopia control group to the NRG-1 antibody groups and the normal control group. The relative NRG-1 mRNA expression in the retina was higher (p < 0.01) in the myopic control group than in the NRG-1 antibody groups and normal control group. Scleral and retinal thickness decreased from the normal control group to the NRG-1 antibody groups to the myopic control group. After intraocular injection of NRG-1 protein, there was a slight dose-dependent increase in the difference in axial length between the right and left eye, however not statistically significantly, from the normal control group (-0.02 ± 0.09 mm) to the high-dose NRG-1 protein group (0.03 ± 0.03 mm; p = 0.12).

Conclusion

Intravitreal NRG-1 antibody application was dose-dependently and time-dependently associated with a reduction in negative lens-induced axial elongation in young guinea pigs.

The Role of Posterior Neural Plate-Derived Presomitic Mesoderm (PSM) in Trunk and Tail Muscle Formation and Axis Elongation

Elongation of the posterior body axis is distinct from that of the anterior trunk and head. Early drivers of posterior elongation are the neural plate/tube and notochord, later followed by the presomitic mesoderm (PSM), together with the neural tube and notochord. In axolotl, posterior neural plate-derived PSM is pushed posteriorly by convergence and extension of the neural plate. The PSM does not go through the blastopore but turns anteriorly to join the gastrulated paraxial mesoderm. To gain a deeper understanding of the process of axial elongation, a detailed characterization of PSM morphogenesis, which precedes somite formation, and of other tissues (such as the epidermis, lateral plate mesoderm and endoderm) is needed. We investigated these issues with specific tissue labelling techniques (DiI injections and GFP⁺ tissue grafting) in combination with optical tissue clearing and 3D reconstructions. We defined a spatiotemporal order of PSM morphogenesis that is characterized by changes in collective cell behaviour. The PSM forms a cohesive tissue strand and largely retains this cohesiveness even after epidermis removal. We show that during embryogenesis, the PSM, as well as the lateral plate and endoderm move anteriorly, while the net movement of the axis is posterior.

Myopia progression after cessation of low-dose atropine eyedrops treatment: A two-year randomized, double-masked, placebo-controlled, cross-over trial

PURPOSE

The purpose of the study was to evaluate myopia progression and axial elongation after stopping 0.01% atropine eye drops through a 2-year cross-over study.

METHODS

This study was a randomized, double-masked, placebo-controlled, cross-over trial in mainland China. 220 children aged 6-12 years with spherical equivalent range of -1.00 D to -6.00 D in both eyes were enrolled in Phase 1 for 1 year. Children who had completed the first year's follow-up continued in the second phase. In Phase 2, the placebo group was crossed over to the 0.01% atropine group (referred to as the 'placebo-atropine group'), and the 0.01% atropine group was crossed over to the placebo group (referred to as the 'atropine-placebo group'). All children underwent the examination of cycloplegic refraction and axial length at a 6-month interval. Only data from right eyes were included in analysis.

RESULTS

One hundred thirty-three subjects completed 2 years of follow-up. In the first year, the mean myopia progression in atropine-placebo group was 0.21 ± 0.08 D slower than that in placebo-atropine group. After cross-over treatment, the mean myopia progression in atropine-placebo group was 0.22 ± 0.07D faster than that in placebo-atropine group in the second year. Over 2 years, the mean myopia progression was -1.26 ± 0.66D and -1.25 ± 0.70D in the atropine-placebo and placebo-atropine groups (p = 0.954).

CONCLUSIONS

The difference in myopia progression between atropine-placebo group and placebo-atropine group in Phase 1 was similar to Phase 2 during the cross-over treatment. Through our cross-over trial, the results suggest that there is no rebound effect after using 0.01% atropine eye drops to prevent progression of myopia.

Anatomic Peculiarities Associated with Axial Elongation of the Myopic Eye

PURPOSE

To describe anatomical peculiarities associated with axial elongation in the human myopic eye.

METHODS

Reviewing the results of previous histomorphometrical investigations of enucleated human globes, as well as reviewing findings obtained in population-based studies and hospital-based clinical investigations of myopic patients and non-myopic individuals.

RESULTS

Myopic axial elongation is associated with a change from a mostly spherical eye shape to a prolate ellipsoid form. It is combined with choroidal and scleral thinning, most pronounced at the posterior pole and less pronounced in the fundus midperiphery. In the fundus midperiphery, the retina and density of the retinal pigment epithelium (RPE) and photoreceptors decrease with a longer axial length, while in the macular region, retinal thickness, RPE cell density, and choriocapillaris thickness are not related to axial length. With axial elongation, a parapapillary gamma zone develops, leading to an enlargement of the optic disc-fovea distance and a decrease in angle kappa. Axial elongation is also correlated with an increase in the surface and volume of Bruch's membrane (BM), while BM thickness remains unchanged. Axial elongation causes moderately myopic eyes to show a shift of BM opening to the foveal direction so that the horizontal disc diameter becomes shorter (with a consequent vertical ovalization of the optic disc shape), a temporal gamma zone develops, and the optic nerve exit takes an oblique course. Features of high myopia are an enlargement of the RPE opening (myopic parapapillary beta zone) and BM opening (secondary macrodisc), elongation and thinning of the lamina cribrosa, peripapillary scleral flange (parapapillary delta zone) and peripapillary choroidal border tissue, secondary BM defects in the macular region, myopic maculoschisis, macular neovascularization, and cobblestones in the fundus periphery.

CONCLUSIONS

These features combined may be explained by a growth in BM in the fundus midperiphery leading to axial elongation.

Controlling organoid symmetry breaking uncovers an excitable system underlying human axial elongation

The human embryo breaks symmetry to form the anterior-posterior axis of the body. As the embryo elongates along this axis, progenitors in the tail bud give rise to tissues that generate spinal cord, skeleton, and musculature. This raises the question of how the embryo achieves axial elongation and patterning. While ethics necessitate in vitro studies, the variability of organoid systems has hindered mechanistic insights. Here, we developed a bioengineering and machine learning framework that optimizes organoid symmetry breaking by tuning their spatial coupling. This framework enabled reproducible generation of axially elongating organoids, each possessing a tail bud and neural tube. We discovered that an excitable system composed of WNT/FGF signaling drives elongation by inducing a neuromesodermal progenitor-like signaling center. We discovered that instabilities in the excitable system are suppressed by secreted WNT inhibitors. Absence of these inhibitors led to ectopic tail buds and branches. Our results identify mechanisms governing stable human axial elongation.

The relationship between baseline axial length and axial elongation in myopic children undergoing orthokeratology

PURPOSE

To investigate the correlation between the baseline axial length (AL) and axial elongation in myopes undergoing orthokeratology (ortho-k).

METHODS

This was a retrospective study. During the 1-year follow-up, 1176 children (aged 8-14 years) were included and divided into an ortho-k group (n = 588) and a single-vision spectacle group (n = 588). The ortho-k group participants (8-11 years of age) who completed the 3-year follow-up (n = 150) were further divided into three subgroups stratified by their baseline AL: subgroup 1 (AL < 24.5 mm), subgroup 2 (24.5 ≤ AL < 26 mm) and subgroup 3 (AL ≥ 26 mm). AL was measured at baseline and during the annual visit.

RESULTS

The ortho-k group exhibited slower 1-year axial elongation (39% reduction) than the spectacle group. The 1-year axial elongation was negatively correlated with initial age in both groups. A negative association between 1-year axial elongation and baseline AL was observed in the ortho-k group but not in the spectacle group. However, this relationship only existed in ortho-k participants 8-11 years of age. For the younger ortho-k participants who completed the 3-year follow-up, the annual axial elongation was significantly higher in subgroup 1 for the first and second years but not in the third year compared with subgroups 2 and 3.

CONCLUSION

Axial elongation was negatively correlated with baseline AL in the ortho-k group. Children aged 8-11 years with longer baseline AL (≥24.5 mm) demonstrated slower annual axial elongation during the first 2 years of ortho-k treatment, which may provide insight into establishing individual guidelines for controlling myopia using ortho-k in children with different baseline characteristics.

The Effect of Citicoline on the Expression of Matrix Metalloproteinase-2 (MMP-2), Transforming Growth Factor-β1 (TGF-β1), and Ki-67, and on the Thickness of Scleral Tissue of Rat Myopia Model

Citicoline, presumed to be involved in the dopaminergic pathway, might play a role as a candidate agent in controlling myopia. However, its study with respect to myopia is limited. The aim of this study is to demonstrate the effect of citicoline on the expression of MMP-2, TGF-β1, and Ki-67, and on the thickness of scleral tissue of a rat myopia model. Immunohistochemistry was performed to evaluate the expression of MMP-2, TGF-β1, and Ki-67 as the markers for fibroblast proliferation. Hematoxylin and eosin staining were used to evaluate scleral thickness. An electronic digital caliper was used to evaluate the axial length. The treatment group administered with 200 mg/kg BW/day had the lowest mean MMP-2 expression, axial elongation, and fibroblast proliferation, but it had the highest mean scleral thickness. The treatment group administered with 300 mg/kg BW/day had the highest mean TGF-β1 expression. Citicoline is able to decrease MMP-2 expression and fibroblast proliferation and increase TGF-β1 expression and scleral tissue thickness significantly in the scleral tissue of rat models for myopia.

The organizing role of Wnt signaling pathway during arthropod posterior growth

Wnt signaling pathways are recognized for having major roles in tissue patterning and cell proliferation. In the last years, remarkable progress has been made in elucidating the molecular and cellular mechanisms that underlie sequential segmentation and axial elongation in various arthropods, and the canonical Wnt pathway has emerged as an essential factor in these processes. Here we review, with a comparative perspective, the current evidence concerning the participation of this pathway during posterior growth, its degree of conservation among the different subphyla within Arthropoda and its relationship with the rest of the gene regulatory network involved. Furthermore, we discuss how this signaling pathway could regulate segmentation to establish this repetitive pattern and, at the same time, probably modulate different cellular processes precisely coupled to axial elongation. Based on the information collected, we suggest that this pathway plays an organizing role in the formation of the body segments through the regulation of the dynamic expression of segmentation genes, via controlling the caudal gene, at the posterior region of the embryo/larva, that is necessary for the correct sequential formation of body segments in most arthropods and possibly in their common segmented ancestor. On the other hand, there is insufficient evidence to link this pathway to axial elongation by controlling its main cellular processes, such as convergent extension and cell proliferation. However, conclusions are premature until more studies incorporating diverse arthropods are carried out.

Manual and software-based measurements of treatment zone parameters and characteristics in children with slow and fast axial elongation in orthokeratology

PURPOSE

To compare the treatment zone (TZ) measurements obtained using manual and software-based methods in orthokeratology (ortho-k) subjects and explore the TZ characteristics of children with slow and fast axial elongation after ortho-k.

METHODS

Data from 69 subjects (aged 7 to <13 years old), who participated in three 24-month longitudinal orthokeratology studies, showing fast (>0.27 mm, n = 38) and slow (<0.09 mm, n = 31) axial elongation, were retrieved. The TZ after ortho-k was defined as the central flattened area enclosed by points with no refractive power change. TZ parameters, including decentration, size, width of the peripheral steepened zone (PSZ), central and peripheral refractive power changes and peripheral rate of power change, were determined manually and using python-based software. TZ parameters were compared between measurement methods and between groups.

RESULTS

Almost all TZ parameters measured manually and with the aid of software were significantly different (p < 0.05). Differences in decentration, size and the PSZ width were not clinically significant, but differences (0.45 to 0.92 D) in refractive power change in the PSZ were significant, although intraclass coefficients (0.95 to 0.98) indicated excellent agreement between methods. Significantly greater TZ decentration, smaller TZ size and greater inferior rate of power change (relative to the TZ centre) were observed in slow progressors using both methods, suggesting a potential role of TZ in regulating myopia progression in ortho-k.

CONCLUSION

TZ measurements using manual and software-based methods differed significantly and cannot be used interchangeably. The combination of TZ decentration, TZ size and peripheral rate of power change may affect myopia control effect in ortho-k.

Factors associated with faster axial elongation after orthokeratology treatment

Background

To study the baseline factors that related to faster axial elongation after orthokeratology (OK) treatment and the characteristics of cases with axial length decrease in a group of myopia children.

Methods

This is a retrospective study. The records of 73 children who had wear OK lens for at least one year were reviewed. Only the data of right eyes were included. Baseline data included: age, gender, parental myopia, refractive error, corneal power, central corneal thickness, axial length and anterior chamber depth. Corneal power, central corneal thickness, anterior chamber depth and axial length after one-year of OK lens wear were also collected. The related factors affecting axial length change were analyzed. A comparison was made on the cases of axial length increase and axial length decrease.

Results

Of the 73 eyes, axial length increased by 0.18 ± 0.17 mm (P < 0.001) after one year of OK lens wear. Correlation analysis showed that one-year axial length change was negatively correlated with age and positively correlated with the parental myopia and baseline myopia. Stepwise multiple linear regression analysis showed that the factors associated with faster axial elongation were lower baseline myopic spherical equivalent (P = 0.018), higher parental myopia degree (P = 0.026), and younger age at the onset of lens wear. (P = 0.039). Nine eyes showed negative axial growth (−0.06 ± 0.04 mm), and had older initial age of lens wear, higher baseline myopic spherical equivalent, and lager baseline corneal power, when compared with cases of axial length increase.

Conclusions

Myopia children with lower baseline myopic spherical equivalent, younger initial age and higher parental myopia had faster axial elongation after orthokeratology treatment. More aggressive treatment should be considered. In children with slow axial elongation, OK lens wear may lead to negative axial growth. Whether there are reasons other than central corneal thinning and choroidal thickening needs further study.

Histopathology of myopic cobblestones

PURPOSE

To search for the histological correlate of peripheral 'cobblestones' in highly myopic eyes.

METHODS

The histomorphometric investigation included histologic sections of enucleated eyes of Caucasian patients. Using light microscopy, we measured the thickness of the retina, Bruch's membrane (BM) and choriocapillaris.

RESULTS

The study included 50 eyes (mean age:60.6 ± 18.7 years;axial length:26.5 ± 3.8 mm), with cobblestone regions detected in 7 eyes. BM thickness and choriocapillaris thickness in the cobblestone region were thinner (1.1 ± 0.2 µm versus 2.4 ± 0.8 µm; p < 0.001 and 1.6 ± 0.5 µm versus 2.6 ± 1.9 µm; p = 0.02, respectively), and just outside of the cobblestone region they were thicker (3.3 ± 0.6 µm versus 2.4 ± 0.8 µm; p = 0.005 and 5.7 ± 1.6 µm versus 2.6 ± 1.9 µm; p = 0.002, respectively) than in corresponding regions of eyes without cobblestones. Within the group of eyes with cobblestones, BM thickness (1.1 ± 0.2 mm versus 3.3 ± 0.6 mm; p < 0.001), choriocapillaris thickness (1.6 ± 0.5 mm versus 5.7 ± 1.6 mm; p < 0.001) and choriocapillaris density (48±15 µm/300 µm versus 159 ± 66 µm/300 µm;PP=0.002) were significantly lower in the cobblestone region than just outside of the cobblestone region. The cobblestone regions were characterized by firm adhesion of disorganized retina with thinned BM, few retinal pigment epithelium (RPE) islands within cobblestone regions, and absence of regional scleral or overall choroidal thinning. BM was mono-layered within, and double-layered outside of cobblestone regions, with the inner layer missing within the cobblestone region (except for the RPE islands).

CONCLUSIONS

Peripheral cobblestone regions in highly myopic eyes are characterized by marked BM thinning with absence of an inner BM layer, almost complete RPE absence, choriocapillaris thinning and firm connection of a disorganized retina to BM. These findings may help elucidating the process of axial elongation in myopic eyes.

Involvement of Oct4-type transcription factor Pou5f3 in posterior spinal cord formation in zebrafish embryos

In vertebrate embryogenesis, elongation of the posterior body is driven by de novo production of the axial and paraxial mesoderm as well as the neural tube at the posterior end. This process is presumed to depend on the stem cell-like population in the tail bud region, but the details of the gene regulatory network involved are unknown. Previous studies suggested the involvement of pou5f3, an Oct4-type POU gene in zebrafish, in axial elongation. In the present study, we first found that pou5f3 is expressed mainly in the dorsal region of the tail bud immediately after gastrulation, and that this expression is restricted to the posterior-most region of the elongating neural tube during somitogenesis. This pou5f3 expression was complementary to the broad expression of sox3 in the neural tube, and formed a sharp boundary with specific expression of tbxta (orthologue of mammalian T/Brachyury) in the tail bud, implicating pou5f3 in the specification of tail bud-derived cells toward neural differentiation in the spinal cord. When pou5f3 was functionally impaired after gastrulation by induction of a dominant-interfering pou5f3 mutant gene (en-pou5f3), trunk and tail elongation were markedly disturbed at distinct positions along the axis depending on the stage. This finding showed involvement of pou5f3 in de novo generation of the body from the tail bud. Conditional functional abrogation also showed that pou5f3 downregulates mesoderm-forming genes but promotes neural development by activating neurogenesis genes around the tail bud. These results suggest that pou5f3 is involved in formation of the posterior spinal cord.

Long-term longitudinal changes in axial length in the Caucasian myopic and hyperopic population with a phakic intraocular lens

Purpose

To determine the long‐term longitudinal axial length changes in myopic and hyperopic adults with an iris‐fixated phakic intraocular lens (pIOL).

Methods

The medical records of patients aged ≥18 years with myopia or hyperopia who were treated with pIOL implantation between 1996 and 2011 for refractive correction with a minimum follow‐up of 5 years after pIOL implantation were analyzed. The main outcome measure was change in ocular axial length over time.

Results

149 eyes of 149 myopic patients and 27 hyperopic eyes of 27 patients were included in this study. Mean patient age was 37.1 ± 10.4 years (35% male) in the myopic group and 39.4 ± 9.4 years (4% male) in the hyperopic group. The eyes of the myopic patients showed a significant mean increase in axial length of 0.45 ± 0.61 mm after a mean follow‐up time of 144 ± 38 months (p < 0.001). In 26 eyes (17%), the axial length had increased by ≥1 mm. The mean annual axial length increase was 0.04 ± 0.06 mm. Axial elongation was associated with a higher degree of myopia (p < 0.001) and younger age (p = 0.02). The eyes of the hyperopic patients showed no change in axial length over time.

Conclusions

Myopic eyes corrected with an iris‐fixated pIOL show continuous increase in axial length at an adult age. Although this study is limited to subjects with a pIOL, this is the first time myopization in Caucasian adults has been reported in a large long‐term longitudinal study.

Anteroposterior Wnt-RA Gradient Defines Adhesion and Migration Properties of Neural Progenitors in Developing Spinal Cord

Mammalian embryos exhibit a transition from head morphogenesis to trunk elongation to meet the demand of axial elongation. The caudal neural tube (NT) is formed with neural progenitors (NPCs) derived from neuromesodermal progenitors localized at the tail tip. However, the molecular and cellular basis of elongating NT morphogenesis is yet elusive. Here, we provide evidence that caudal NPCs exhibit strong adhesion affinity that is gradually decreased along the anteroposterior (AP) axis in mouse embryonic spinal cord and human cellular models. Strong cell-cell adhesion causes collective migration, allowing AP alignment of NPCs depending on their birthdate. We further validated that this axial adhesion gradient is associated with the extracellular matrix and is under the control of graded Wnt signaling emanating from tail buds and antagonistic retinoic acid (RA) signaling. These results suggest that progressive reduction of NPC adhesion along the AP axis is under the control of Wnt-RA molecular networks, which is essential for a proper elongation of the spinal cord.

A Tgfbr1/Snai1-dependent developmental module at the core of vertebrate axial elongation

Formation of the vertebrate postcranial body axis follows two sequential but distinct phases. The first phase generates pre-sacral structures (the so-called primary body) through the activity of the primitive streak on axial progenitors within the epiblast. The embryo then switches to generate the secondary body (post-sacral structures), which depends on axial progenitors in the tail bud. Here we show that the mammalian tail bud is generated through an independent functional developmental module, concurrent but functionally different from that generating the primary body. This module is triggered by convergent Tgfbr1 and Snai1 activities that promote an incomplete epithelial to mesenchymal transition on a subset of epiblast axial progenitors. This EMT is functionally different from that coordinated by the primitive streak, as it does not lead to mesodermal differentiation but brings axial progenitors into a transitory state, keeping their progenitor activity to drive further axial body extension.

Cellulose synthase interactive1- and microtubule-dependent cell wall architecture is required for acid growth in Arabidopsis hypocotyls

Auxin-induced cell elongation relies in part on the acidification of the cell wall, a process known as acid growth that presumably triggers expansin-mediated wall loosening via altered interactions between cellulose microfibrils. Cellulose microfibrils are a major determinant for anisotropic growth and they provide the scaffold for cell wall assembly. Little is known about how acid growth depends on cell wall architecture. To explore the relationship between acid growth-mediated cell elongation and plant cell wall architecture, two mutants (jia1-1 and csi1-3) that are defective in cellulose biosynthesis and cellulose microfibril organization were analyzed. The study revealed that cell elongation is dependent on CSI1-mediated cell wall architecture but not on the overall crystalline cellulose content. We observed a correlation between loss of crossed-polylamellate walls and loss of auxin- and fusicoccin-induced cell growth in csi1-3. Furthermore, induced loss of crossed-polylamellate walls via disruption of cortical microtubules mimics the effect of csi1 in acid growth. We hypothesize that CSI1- and microtubule-dependent crossed-polylamellate walls are required for acid growth in Arabidopsis hypocotyls.

Pathogenesis and Prevention of Worsening Axial Elongation in Pathological Myopia

PURPOSE

This review discusses the etiology and pathogenesis of myopia, prevention of disease progression and worsening axial elongation, and emerging myopia treatment modalities.

INTRODUCTION

Pediatric myopia is a public health concern that impacts young children worldwide and is associated with numerous future ocular diseases such as cataract, glaucoma, retinal detachment and other chorioretinal abnormalities. While the exact mechanism of myopia of the human eye remains obscure, several studies have reported on the role of environmental and genetic factors in the disease development.

METHODS

A review of literature was conducted. PubMed and Medline were searched for combinations and derivatives of the keywords including, but not limited to, "pediatric myopia", "axial elongation", "scleral remodeling" or "atropine." The PubMed and Medline database search were performed for randomized control trials, systematic reviews and meta-analyses using the same keyword combinations.

RESULTS

Studies have reported that detection of genetic correlations and modification of environmental influences may have a significant impact in myopia progression, axial elongation and future myopic ocular complications. The conventional pharmacotherapy of pediatric myopia addresses the improvement in visual acuity and prevention of amblyopia but does not affect axial elongation or myopia progression. Several studies have published varying treatments, including optical, pharmacological and surgical management, which show great promise for a more precise control of myopia and preservation of ocular health.

DISCUSSION

Understanding the role of factors influencing the onset and progression of pediatric myopia will facilitate the development of successful treatments, reduction of disease burden, arrest of progression and improvement in future of the management of myopia.

Pattern of Axial Length Growth in Children Myopic Anisometropes with Orthokeratology Treatment

PURPOSE

To compare the pattern of growth in axial length (AL) between children with anisometropia who wear orthokeratology (OK) lenses and those who wear spectacles (SP).

METHODS

A retrospective study was conducted. Data of baseline and 1 year from 252 children (8-14 years old) anisomyopes who sought refraction corrections at the Zhongshan Ophthalmic Center between October 2013 and June 2017 were reviewed. Seventy-nine unilateral myopic anisometropes (UMA) and 98 bilateral myopic anisometropes (BMA) treated with OK lenses were set as study groups (OK-UMA and OK-BMA groups). Age, refraction, and AL-matched unilateral (n = 38) and bilateral myopic anisometropes (n = 37) treated with spectacles were set as control groups (SP-UMA and SP-BMA groups). The 1-year change in AL between the study and control groups (OK-UMA vs. SP-UMA and OK-BMA vs. SP-BMA) was compared.

RESULTS

There were no significant differences in the baseline of age, refraction, and AL between OK-UMA and SP-UMA or OK-BMA and SP-BMA groups (all P > .05). Compared to the SP-UMA group, annual axial elongation of the myopic eyes of the OK-UMA group was smaller (0.05 ± 0.19 mm vs. 0.33 ± 0.29 mm, P < .001); however, AL elongation in the non-myopic eyes were comparable between SP-UMA and OK-UMA groups (P > .05). At the end of 1 year, the interocular difference in AL (aniso-AL) decreased by 0.29 ± 0.29 mm (P < .001) in the OK-UMA group but remained unchanged in SP-UMA group. Compared to the SP-BMA group, annual axial elongations of both eyes of the OK-BMA group were smaller (the more myopic eye, 0.05 ± 0.17 mm vs. 0.38 ± 0.21 mm; the less myopic eye, 0.15 ± 0.19 mm vs. 0.35 ± 0.28 mm; both P < .001). At the end of 1 year, aniso-AL decreased by 0.10 ± 0.15 mm (P < .001) in the OK-BMA group but remained unchanged in the SP-BMA group.

CONCLUSION

Orthokeratology is effective in reducing the interocular difference in AL of children anisomyopes through greater retardation of axial elongation of the more myopic eyes.

Myopia: Anatomic Changes and Consequences for Its Etiology

The process of emmetropization is the adjustment of the length of the optical axis to the given optical properties of the cornea and lens after the end of the second year of life. Up to the end of the second year of life, the eye grows spherically. Axial elongation in the process of emmetropization after the second year of life is associated with a thinning of the retina and a reduced density of retinal pigment epithelium (RPE) cells in the equatorial and retroequatorial region, and a thinning of the choroid and sclera, starting at the equator and being most marked at the posterior pole. In contrast, retinal thickness and RPE density in the macular region and thickness of Bruch membrane (BM) in any region are independent of axial length. It led to the hypothesis that axial elongation occurs by the production of additional BM in the equatorial and retroequatorial region leading to a decreased RPE density and retinal thinning in that region and a more tube-like than spherical enlargement of the globe, without compromise in the density of the macular RPE cells and in macular retinal thickness. The increased disc-fovea distance in axially myopic eyes is caused by the development and enlargement of parapapillary, BM-free, gamma zone, whereas the length of macular BM, and indirectly macular RPE cell density, and macular retinal thickness, remain constant.

Temporal regulation of Lin28a during mammalian neurulation contributes to neonatal body size control

BACKGROUND

The timing of developmental events is tightly regulated along a time axis for normal development. Although the RNA-binding protein Lin28a plays a crucial role in the regulation of developmental timing in Caenorhabditis elegans, how the timing of Lin28a expression affects the rate and/or duration of developmental events during mammalian development remains to be addressed.

RESULTS

In this study, we discovered that the timing and the duration of Lin28a expression affect embryonic growth. During the neurulation stage of mouse development, endogenous Lin28a levels start to drop. When Lin28a expression was maintained transiently using the inducible tetracycline-regulated gene expression (Tet-ON) system [doxycycline (Dox)-inducible Lin28a transgenic (iLin28a Tg) mice] with Dox administration at E8.5 and E9.5, it resulted in neonatal lethality, increased body weight (organomegaly), and an increased number of caudal vertebrae at birth. On the other hand, Lin28a induction only at E8.5 caused neonatal lethality and organomegaly, but did not affect the caudal vertebra number. Of note, although Dox treatment before or after neurulation still caused neonatal lethality, it neither caused organomegaly nor the increased caudal vertebra number in iLin28a Tg neonates.

CONCLUSIONS

Temporal regulation of Lin28a expression during neurulation affects developmental events such as cessation of axial elongation and embryonic growth in mice.

Outdoor Jogging and Myopia Progression in School Children From Rural Beijing: The Beijing Children Eye Study

Purpose

To assess the influence of an outdoor program on myopia progression in school children.

Methods

The prospective interventional school-based study included 373 students aged 6 to 7 years (grade 1 or 2) who were examined annually between 2012 and 2016. Between 2012 and 2013, the children in the study group (n = 157) performed a 30-minute jogging exercise every school day, while the children in the control school (n = 216) did not. All children underwent a comprehensive ocular examination, including biometry.

Results

At 1 year after baseline, axial elongation and progression of myopic refractive error were significantly lower in the study group than in the control group. Study group and control group differed in axial elongation only in the subgroup of children nonmyopic at baseline, while axial elongation in the children myopic at baseline did not differ between both groups. At 1 and 2 years after the outdoor program stopped, increase in axial length was significantly larger in the study group. At 4 years after baseline, study group and control group did not differ significantly in total axial elongation and total change in refractive error.

Conclusions

An outdoor program of 30 minutes performed every school day for 1 year temporarily reduced myopia progression in schoolchildren nonmyopic at baseline, with a complete rebound effect after the program ended within the 3 following years.

Translational Relevance

An outdoor program of 30 minutes performed every school day for 1 year temporarily reduced the progression of myopia in schoolchildren nonmyopic at baseline for the period when the program was carried out.

Retinoic acid signaling reduction recapitulates the effects of alcohol on embryo size

Intrauterine growth restriction (IUGR) is commonly observed in human pregnancies and can result in severe clinical outcomes. IUGR is observed in Fetal Alcohol Syndrome (FAS) fetuses as a result of alcohol (ethanol) exposure during pregnancy. To further understand FAS, the severe form of Fetal Alcohol Spectrum Disorder, we performed an extensive quantitative analysis of the effects of ethanol on embryo size utilizing our Xenopus model. Ethanol-treated embryos exhibited size reduction along the anterior-posterior axis. This effect was evident primarily from the hindbrain caudally, while rostral regions appeared refractive to ethanol-induced size changes, also known as asymmetric IUGR. Interestingly, some embryo batches in addition to shortening from the hindbrain caudally also exhibited an alcohol-dependent reduction of the anterior head domain, known as symmetric IUGR. To study the connection between ethanol exposure and reduced retinoic acid levels we treated embryos with the retinaldehyde dehydrogenase inhibitors, DEAB and citral. Inhibition of retinoic acid biosynthesis recapitulated the growth defects induced by ethanol affecting mainly axial elongation from the hindbrain caudally. To study the competition between ethanol clearance and retinoic acid biosynthesis we demonstrated that, co-exposure to alcohol reduces the teratogenic effects of treatment with retinol (vitamin A), the retinoic acid precursor. These results further support the role of retinoic acid in the regulation of axial elongation.

Optic disc-fovea distance and myopia progression in school children: the Beijing Children Eye Study

PURPOSE

To assess changes in the optic disc-fovea distance (DFD) with progressing myopia in school children.

METHODS

The school-based, prospective, longitudinal study included grade-1 children in 2011 who were yearly re-examined until 2016. We measured DFD, optic disc diameters and width of parapapillary gamma zone (parapapillary region without Bruch's membrane (BM)) on fundus photographs.

RESULTS

Of 382 grade-1 children examined in 2011, 294 (77.0%) children (mean age in 2011: 6.4 ± 0.5 years) returned to be examined in 2016. In relative terms, the increase in DFD (1.15 ± 0.33 mm) was more due to an increase in gamma zone width (+300% or 0.29 ± 0.30 mm) than an increase in macular BM length (+18% or 0.74 ± 0.21 mm). In multivariate regression analysis, longer increase in DFD was correlated (regression coefficient r²  = 0.79) with longer axial elongation during the study period (p < 0.001; standardized regression coefficient β: 0.61; non-standardized regression coefficient B: 0.30; 95% confidence interval (CI): 0.26, 0.33), larger increase in gamma zone width (p < 0.001; β: 0.35; B: 0.40; 95%CI: 0.32, 0.48) and longer axial length in 2011 (p = 0.01; β:0.07; B:0.03; 95%CI:0.01, 0.06). Larger increase in gamma zone width was associated (r²  = 0.73) with larger increase in DFD (p < 0.001; β: 0.51; B: 0.46; 95%CI: 0.39, 0.53), larger increase in the vertical-to-horizontal disc diameter ratio (p < 0.001; β: 0.43; B:1.21; 95%CI: 1.00, 1.42) and longer vertical disc diameter (p < 0.001; β: 0.15; B:0.24; 95%CI: 0.14, 0.34).

CONCLUSION

In adolescent school children, axial elongation-associated increase in DFD was mainly due to an enlargement (+300%) of parapapillary gamma zone, while macular BM length increased to minor degree (+18%). Gamma zone enlargement was correlated with axial elongation-associated vertical optic disc rotation, potentially due to an increased backward pull of the optic nerve on the temporal optic disc border.

Comparison of myopia control between toric and spherical periphery design orthokeratology in myopic children with moderate-to-high corneal astigmatism

AIM

To compare clinical results between toric and spherical periphery design orthokeratology (ortho-k) in myopic children with moderate-to-high corneal astigmatism.

METHODS

This retrospective study enrolled 62 eyes of 62 subjects using toric ortho-k lenses. These subjects were assigned to the toric group. Based on the one-to-one match principle (same age, proximate spherical equivalence and corneal astigmatism), 62 eyes of 62 subjects were enrolled and included in the spherical group. At one-year follow-up visit, visual acuity, corneal astigmatism, treatment zone decentration, axial elongation and adverse reaction were compared between these two groups.

RESULTS

At the one-year visit, corneal astigmatism was significantly lower in the toric group (1.22±0.76 D) than in the spherical group (2.05±0.85 D) (P=0.012). The mean magnitude of the treatment zone decentration was 0.62±0.42 mm in the toric group and 1.07±0.40 mm in the spherical group (P=0.004). Axial elongation was significantly slower in the toric group (0.04±0.13 mm) than in the spherical group (0.09±0.13 mm) (P=0.001). The one-year axial elongation was significantly correlated with initial age (r=-0.487, P<0.001) and periphery design of ortho-k lens (r=0.315, P<0.001). The incidence of corneal staining was lower in the toric group (8.1%) than in the spherical group (19.4%) (P<0.001).

CONCLUSION

Toric periphery design ortho-k lenses may provide lower corneal astigmatism, better centration, slower axial elongation and lower incidence of corneal staining in myopic children with moderate-to-high corneal astigmatism.

A Gradient of Glycolytic Activity Coordinates FGF and Wnt Signaling during Elongation of the Body Axis in Amniote Embryos

Mammalian embryos transiently exhibit aerobic glycolysis (Warburg effect), a metabolic adaptation also observed in cancer cells. The role of this particular type of metabolism during vertebrate organogenesis is currently unknown. Here, we provide evidence for spatiotemporal regulation of glycolysis in the posterior region of mouse and chicken embryos. We show that a posterior glycolytic gradient is established in response to graded transcription of glycolytic enzymes downstream of fibroblast growth factor (FGF) signaling. We demonstrate that glycolysis controls posterior elongation of the embryonic axis by regulating cell motility in the presomitic mesoderm and by controlling specification of the paraxial mesoderm fate in the tail bud. Our results suggest that glycolysis in the tail bud coordinates Wnt and FGF signaling to promote elongation of the embryonic axis.

An examination of the relation between intraocular pressure, fundal stretching and myopic pathology

Pathological myopia is one of the leading causes of visual impairment worldwide. Myopic development and progression is biomechanical and dominated by axial elongation. This clinical perspective examines some of the stretch-related fundal changes, which are associated with axial elongation and myopic pathology. The biomechanics of stretching of the fundus appears to depend on genetically and/or visual experience-based scleral changes, which reduce its thickness and elastic modulus so that it becomes more susceptible to the distending forces of intraocular pressure. These changes include reduced collagen synthesis, altered collagen fibres, tissue loss, altered proteoglycans and increased matrix metalloproteinase activity. Such changes are associated with reduced scleral rigidity and related increased potential to stretch in response to intraocular pressure. As axial elongation progresses, the sclera appears likely to continue to reduce in thickness and in its capacity to resist intraocular pressure, especially when pressure becomes elevated. Tessellation, lacquer cracks, myopic crescents, staphylomata, chorioretinal atrophy and retinal detachment are examined within a model for stretching of the fundus. Age, refractive error and axial length, for example, are associated with increased pathological progression. Myopic pathological progression can become dominated by vascular changes and include a greater risk of loss of acuity and blindness. Measures to control myopic pathology, which successfully slow or prevent stretching of the fundus, appear to be key factors in reducing or even avoiding permanent visual loss associated with this condition. For example, limiting axial elongation and related myopic fundus pathology by inhibiting changes which reduce the elastic modulus of scleral tissue is a desirable outcome from interventions to control myopia. Similarly, reducing exposure to the distending stress of elevated intraocular pressure appears to be a desirable form of intervention to control myopia, especially if myopic pathology can be reduced or prevented.

Myopia control with positively aspherized progressive addition lenses: a 2-year, multicenter, randomized, controlled trial

PURPOSE

To evaluate the effect of newly designed positively aspherized progressive addition lenses (PA-PALs), which reduce both lag of accommodation and hyperopic defocus on the peripheral retina, on the progression of early-onset myopia.

METHODS

Positively aspherized-PALs have near addition and high positive distance zone aspherization comparable to the addition power. One hundred ninety-seven children were enrolled, 6 to 12 years of age, with spherical equivalent refraction from -1.00 to -4.50 diopters (D). The children were randomized to receive one of three lenses: single vision lenses (SVLs), PA-PALs with +1.0 D addition, or PA-PALs with +1.5 D addition. Follow-up visits occurred every 6 months for 2 years. The primary outcome was myopia progression evaluated by cycloplegic autorefraction.

RESULTS

One hundred sixty-nine (86%) children completed the follow-up. Statistical analysis of adjusted progression rates showed a mean (±SE) progression of -1.39 ± 0.09 D in the control group wearing SVLs at the 24-month visit. Statistically significant (P = 0.017) retardation of myopia progression (0.27 ± 0.11 D during 24-month period or reduction ratio of 20%) by +1.5 D add PA-PALs relative to the SVLs was found, which was within the range of the percentage efficacy of myopia retardation by the conventional PALs in earlier trials over the same follow-up period. Nearly all retardation occurred in the first 12 months with no significant efficacy in the second year. Positively aspherized-PALs with +1.0 D addition showed negligible efficacy.

CONCLUSIONS

To the extent that has been tested and that can be tolerated by wearers of spectacle lenses, the high positive aspherization of the distance zone added to PALs does not enhance their therapeutic efficacy in slowing myopia progression. (http://www.anzctr.org.au/ number, ACTRN12608000566336).

Gene expression signatures in tree shrew choroid during lens-induced myopia and recovery

Gene expression in tree shrew choroid was examined during the development of minus-lens induced myopia (LIM, a GO condition), after completion of minus-lens compensation (a STAY condition), and early in recovery (REC) from induced myopia (a STOP condition). Five groups of tree shrews (n = 7 per group) were used. Starting 24 days after normal eye-opening (days of visual experience [DVE]), one minus-lens group wore a monocular -5 D lens for 2 days (LIM-2), another minus-lens group achieved stable lens compensation while wearing a monocular -5 D lens for 11 days (LIM-11); a recovery group also wore a -5 D lens for 11 days and then received 2 days of recovery starting at 35 DVE (REC-2). Two age-matched normal groups were examined at 26 DVE and 37 DVE. Quantitative PCR was used to measure the relative differences in mRNA levels in the choroid for 77 candidate genes that were selected based on previous studies or because a whole-transcriptome analysis suggested their expression would change during myopia development or recovery. Small myopic changes were observed in the treated eyes of the LIM-2 group (-1.0 ± 0.2 D; mean ± SEM) indicating eyes were early in the process of developing LIM. The LIM-11 group exhibited complete refractive compensation (-5.1 ± 0.2 D) that was stable for five days. The REC-2 group recovered by 1.3 ± 0.3 D from full refractive compensation. Sixty genes showed significant mRNA expression differences during normal development, LIM, or REC conditions. In LIM-2 choroid (GO), 18 genes were significantly down-regulated in the treated eyes relative to the fellow control eyes and 10 genes were significantly up-regulated. In LIM-11 choroid (STAY), 10 genes were significantly down-regulated and 12 genes were significantly up-regulated. Expression patterns in GO and STAY were similar, but not identical. All genes that showed differential expression in GO and STAY were regulated in the same direction in both conditions. In REC-2 choroid (STOP), 4 genes were significantly down-regulated and 18 genes were significantly up-regulated. Thirteen genes showed bi-directional regulation in GO vs. STOP. The pattern of differential gene expression in STOP was very different from that in GO or in STAY. Significant regulation was observed in genes involved in signaling as well as extracellular matrix turnover. These data support an active role for the choroid in the signaling cascade from retina to sclera. Distinctly different treated eye vs. control eye mRNA signatures are present in the choroid in the GO, STAY, and STOP conditions. The STAY signature, present after full compensation has occurred and the GO visual stimulus is no longer present, may participate in maintaining an elongated globe. The 13 genes with bi-directional expression differences in GO and STOP responded in a sign of defocus-dependent manner. Taken together, these data further suggest that a network of choroidal gene expression changes generate the signal that alters scleral fibroblast gene expression and axial elongation rate.

Juvenile eye growth, when completed? An evaluation based on IOL-Master axial length data, cross-sectional and longitudinal

PURPOSE

To test Sorsby's classical statement of axial eye growth as completed at the age of 13 years, with a view also to differentiating between basic eye growth and juvenile elongation associated with eventual refractive change towards myopia.

METHODS

(i) A total of 160 healthy eyes close to emmetropia were included in a cross-sectional set-up (age 4-20 years, 91 males, 69 females), and (ii) 78 longitudinal data sets (67 male and 11 female annual repeat exams over 2-7 years, n=30; age span 4-19 years) were available for evaluating individual axial elongation. The IOL-Master equipment was preferred for conventional ultrasound oculometry due to its extreme repeatability of measuring values, thus making it well fitted for evaluating very small differences. In particular, this had bearing for the decelerating end phase of growth in the longitudinal investigation.

RESULTS

Sorby's statement about age 13 as general limit found support from the cross-sectional data, which suggested stable emmetropic eye size from about 11-12 years, with an average apparently outgrown male emmetropic value of 23.5 mm versus females' 22.9 mm. The longitudinal data, however, showed emmetropic growth also beyond this age, with individual data to establish continued axial elongation also at age 13-18 years. The final basic teenage growth is however minute and without practical implications.

CONCLUSIONS

Individual ocular growth curves have indicated axial elongation to occur also after the age of 13 years. With regard to the - mainly academic - discrepancy between cross-sectional and longitudinal results, bigger samples are needed, and the juvenile myopic trend has to be acknowledged.

Gene expression signatures in tree shrew sclera in response to three myopiagenic conditions

PURPOSE

We compared gene expression signatures in tree shrew sclera produced by three different visual conditions that all produce ocular elongation and myopia: minus-lens wear, form deprivation, and dark treatment.

METHODS

Six groups of tree shrews (n = 7 per group) were used. Starting 24 days after normal eye-opening (days of visual experience [DVE]), two minus-lens groups wore a monocular -5 diopter (D) lens for 2 days (ML-2) or 4 days (ML-4); two form-deprivation groups wore a monocular translucent diffuser for 2 days (FD-2) or 4 days (FD-4). A dark-treatment (DK) group was placed in continuous darkness for 11 days after experiencing a light/dark environment until 17 DVE. A normal colony-reared group was examined at 28 DVE. Quantitative PCR was used to measure the relative differences in mRNA levels for 55 candidate genes in the sclera that were selected, either because they showed differential expression changes in previous ML studies or because a whole-transcriptome analysis suggested they would change during myopia development.

RESULTS

The treated eyes in all groups responded with a significant myopic shift, indicating that the myopia was actively progressing. In the ML-2 group, 27 genes were significantly downregulated in the treated eyes, relative to control eyes. In the treated eyes of the FD-2 group, 16 of the same genes also were significantly downregulated and one was upregulated. The two gene expression patterns were significantly correlated (r(2) = 0.90, P < 0.001). After 4 days of treatment, 31 genes were significantly downregulated in the treated eyes of the ML-4 group and three were upregulated. Twenty-nine of the same genes (26 down- and 3 up-regulated) and six additional genes (all downregulated) were significantly affected in the FD-4 group. The response patterns were highly correlated (r(2) = 0.95, P < 0.001). When the DK group (mean of right and left eyes) was compared to the control eyes of the ML-4 group, the direction and magnitude of the gene expression patterns were similar to those of the ML-4 (r(2) = 0.82, P < 0.001, excluding PENK). Similar patterns also were found when the treated eyes of the ML-4, FD-4, and DK groups were compared to the age-matched normal eyes.

CONCLUSIONS

The very similar gene expression signatures produced in the sclera by the three different myopiagenic visual conditions at different time points suggests that there is a "scleral remodeling signature" in this mammal, closely related to primates. The scleral genes examined did not distinguish between the specific visual stimuli that initiate the signaling cascade that results in axial elongation and myopia.

Actomyosin stiffens the vertebrate embryo during crucial stages of elongation and neural tube closure

Physical forces drive the movement of tissues within the early embryo. Classical and modern approaches have been used to infer and, in rare cases, measure mechanical properties and the location and magnitude of forces within embryos. Elongation of the dorsal axis is a crucial event in early vertebrate development, yet the mechanics of dorsal tissues in driving embryonic elongation that later support neural tube closure and formation of the central nervous system is not known. Among vertebrates, amphibian embryos allow complex physical manipulation of embryonic tissues that are required to measure the mechanical properties of tissues. In this paper, we measure the stiffness of dorsal isolate explants of frog (Xenopus laevis) from gastrulation to neurulation and find dorsal tissues stiffen from less than 20 Pascal (Pa) to over 80 Pa. By iteratively removing tissues from these explants, we find paraxial somitic mesoderm is nearly twice as stiff as either the notochord or neural plate, and at least 10-fold stiffer than the endoderm. Stiffness measurements from explants with reduced fibronectin fibril assembly or disrupted actomyosin contractility suggest that it is the state of the actomyosin cell cortex rather than accumulating fibronectin that controls tissue stiffness in early amphibian embryos.