Regulation of c-Maf and αA-Crystallin in Ocular Lens by Fibroblast Growth Factor Signaling

Shc1 cooperates with Frs2 and Shp2 to recruit Grb2 in FGF-induced lens development

Fibroblast growth factor (FGF) signaling elicits multiple downstream pathways, most notably the Ras/MAPK cascade facilitated by the adaptor protein Grb2. However, the mechanism by which Grb2 is recruited to the FGF signaling complex remains unresolved. Here, we showed that genetic ablation of FGF signaling prevented murine lens induction by disrupting transcriptional regulation and actin cytoskeletal arrangements, which could be reproduced by deleting the juxtamembrane region of the FGF receptor and rescued by Kras activation. Conversely, mutations affecting the Frs2-binding site on the FGF receptor or the deletion of Frs2 and Shp2 primarily impact later stages of lens vesicle development involving lens fiber cell differentiation. Our study further revealed that the loss of Grb2 abolished MAPK signaling, resulting in a profound arrest of lens development. However, removing Grb2's putative Shp2 dephosphorylation site (Y209) neither produced a detectable phenotype nor impaired MAPK signaling during lens development. Furthermore, the catalytically inactive Shp2 mutation (C459S) only modestly impaired FGF signaling, whereas replacing Shp2's C-terminal phosphorylation sites (Y542/Y580) previously implicated in Grb2 binding only caused placental defects, perinatal lethality, and reduced lacrimal gland branching without impacting lens development, suggesting that Shp2 only partially mediates Grb2 recruitment. In contrast, we observed that FGF signaling is required for the phosphorylation of the Grb2-binding sites on Shc1 and the deletion of Shc1 exacerbates the lens vesicle defect caused by Frs2 and Shp2 deletion. These findings establish Shc1 as a critical collaborator with Frs2 and Shp2 in targeting Grb2 during FGF signaling.

The intrinsic expression of NLRP3 in Th17 cells promotes their protumor activity and conversion into Tregs

Th17 cells can perform either regulatory or inflammatory functions depending on the cytokine microenvironment. These plastic cells can transdifferentiate into Tregs during inflammation resolution, in allogenic heart transplantation models, or in cancer through mechanisms that remain poorly understood. Here, we demonstrated that NLRP3 expression in Th17 cells is essential for maintaining their immunosuppressive functions through an inflammasome-independent mechanism. In the absence of NLRP3, Th17 cells produce more inflammatory cytokines (IFNγ, Granzyme B, TNFα) and exhibit reduced immunosuppressive activity toward CD8+ cells. Moreover, the capacity of NLRP3-deficient Th17 cells to transdifferentiate into Treg-like cells is lost. Mechanistically, NLRP3 in Th17 cells interacts with the TGF-β receptor, enabling SMAD3 phosphorylation and thereby facilitating the acquisition of immunosuppressive functions. Consequently, the absence of NLRP3 expression in Th17 cells from tumor-bearing mice enhances CD8 + T-cell effectiveness, ultimately inhibiting tumor growth.

Shc1 cooperates with Frs2 and Shp2 to recruit Grb2 in FGF-induced lens development

Fibroblast growth factor (FGF) signaling elicits multiple downstream pathways, most notably the Ras/MAPK cascade facilitated by the adaptor protein Grb2. However, the mechanism by which Grb2 is recruited to the FGF signaling complex remains unresolved. Here we showed that genetic ablation of FGF signaling prevented lens induction by disrupting transcriptional regulation and actin cytoskeletal arrangements, which could be reproduced by deleting the juxtamembrane region of the FGF receptor and rescued by Kras activation. Conversely, mutations affecting the Frs2-binding site on the FGF receptor or the deletion of Frs2 and Shp2 primarily impact later stages of lens vesicle development involving lens fiber cell differentiation. Our study further revealed that the loss of Grb2 abolished MAPK signaling, resulting in a profound arrest of lens development. However, removing Grb2's putative Shp2 dephosphorylation site (Y209) neither produced a detectable phenotype nor impaired MAPK signaling during lens development. Furthermore, the catalytically inactive Shp2 mutation (C459S) only modestly impaired FGF signaling, whereas replacing Shp2's C-terminal phosphorylation sites (Y542/Y580) previously implicated in Grb2 binding only caused placental defects, perinatal lethality, and reduced lacrimal gland branching without impacting lens development, suggesting that Shp2 only partially mediates Grb2 recruitment. In contrast, we observed that FGF signaling is required for the phosphorylation of the Grb2-binding sites on Shc1 and the deletion of Shc1 exacerbates the lens vesicle defect caused by Frs2 and Shp2 deletion. These findings establish Shc1 as a critical collaborator with Frs2 and Shp2 in targeting Grb2 during FGF signaling.

IFN-α affects Th17/Treg cell balance through c-Maf and associated with the progression of EBV- SLE

OBJECTIVES

Systemic lupus erythematosus (SLE) is a multi-organ autoimmune disease, of which the pathogens is remains obscure. Viral infection, particularly Epstein Barr viru (EBV) infection, has been considered a common pathogenic factor. This study suggests that c-Maf may be an important target in T cell differentiation during SLE progression, providing a potentially new perspective on the role of viral infection in the pathogenesis of autoimmune diseases.

METHODS

Cytokines of EBV-infected SLE patients were measured by ELISA and assessed in conjunction with their clinical data. IFN-α, c-Maf, and the differentiation of Th17/Treg cells in SLE patients and MRL/LPR mice were analyzed using FCM, WB, RT-PCR, etc. Following the infection of cells and mice with EBV or viral mimic poly (dA:dT), the changes of the aforementioned indicators were investigated. The relationship among IFN-α, STAT3, c-Maf and Th17 cells was determined by si-RNA technique.

RESULTS

Many SLE patients are found to be complicated by viral infections; Further, studies have demonstrated that viral infection, especially EBV, is involved in SLE development. This study showed that viral infections might promote IFN-α secretion, inhibit c-Maf expression by activating STAT3, increase Th17 cell differentiation, and lead to the immune imbalance of Th17/Treg cells, thus playing a role in the onset and progression of SLE.

CONCLUSION

This study demonstrates that EBV infections may contribute to SLE development by activating STAT3 through IFN-α, inhibiting c-Maf, and causing Th17/Treg immune imbalance. Our work provided a new insight into the pathogenesis and treatment of SLE.

Analysis of long-range chromatin contacts, compartments and looping between mouse embryonic stem cells, lens epithelium and lens fibers

BACKGROUND

Nuclear organization of interphase chromosomes involves individual chromosome territories, "open" and "closed" chromatin compartments, topologically associated domains (TADs) and chromatin loops. The DNA- and RNA-binding transcription factor CTCF together with the cohesin complex serve as major organizers of chromatin architecture. Cellular differentiation is driven by temporally and spatially coordinated gene expression that requires chromatin changes of individual loci of various complexities. Lens differentiation represents an advantageous system to probe transcriptional mechanisms underlying tissue-specific gene expression including high transcriptional outputs of individual crystallin genes until the mature lens fiber cells degrade their nuclei.

RESULTS

Chromatin organization between mouse embryonic stem (ES) cells, newborn (P0.5) lens epithelium and fiber cells were analyzed using Hi-C. Localization of CTCF in both lens chromatins was determined by ChIP-seq and compared with ES cells. Quantitative analyses show major differences between number and size of TADs and chromatin loop size between these three cell types. In depth analyses show similarities between lens samples exemplified by overlaps between compartments A and B. Lens epithelium-specific CTCF peaks are found in mostly methylated genomic regions while lens fiber-specific and shared peaks occur mostly within unmethylated DNA regions. Major differences in TADs and loops are illustrated at the ~ 500 kb Pax6 locus, encoding the critical lens regulatory transcription factor and within a larger ~ 15 Mb WAGR locus, containing Pax6 and other loci linked to human congenital diseases. Lens and ES cell Hi-C data (TADs and loops) together with ATAC-seq, CTCF, H3K27ac, H3K27me3 and ENCODE cis-regulatory sites are shown in detail for the Pax6, Sox1 and Hif1a loci, multiple crystallin genes and other important loci required for lens morphogenesis. The majority of crystallin loci are marked by unexpectedly high CTCF-binding across their transcribed regions.

CONCLUSIONS

Our study has generated the first data on 3-dimensional (3D) nuclear organization in lens epithelium and lens fibers and directly compared these data with ES cells. These findings generate novel insights into lens-specific transcriptional gene control, open new research avenues to study transcriptional condensates in lens fiber cells, and enable studies of non-coding genetic variants linked to cataract and other lens and ocular abnormalities.

Case report: Whole exome sequencing identified a novel mutation (p.Y301H) of MAF in a Chinese family with congenital cataracts

Background

Congenital cataracts stand as the primary cause of childhood blindness globally, characterized by clouding of the eye's lens at birth or shortly thereafter. Previous investigations have unveiled that a variant in the V-MAF avian musculoaponeurotic-fibrosarcoma oncogene homolog (MAF) gene can result in Ayme-Gripp syndrome and solitary cataract. Notably, MAF mutations have been infrequently reported in recent years.

Methods

In this investigation, we recruited a Chinese family with non-syndromic cataracts. Whole exome sequencing and Sanger sequencing were applied to scrutinize the genetic anomaly within the family.

Results

Through whole exome sequencing and subsequent data filtration, a new mutation (NM_005360, c.901T>C/p.Y301H) in the MAF gene was detected. Sanger sequencing validated the presence of this mutation in another affected individual. The p.Y301H mutation, situated in an evolutionarily preserved locus, was not detected in our 200 local control cohorts and various public databases. Additionally, multiple bioinformatic programs predicted that the mutation was deleterious and disrupted the bindings between MAF and its targets.

Conclusion

Hence, we have documented a new MAF mutation within a Chinese family exhibiting isolated congenital cataracts. Our study has the potential to broaden the spectrum of MAF mutations, offering insights into the mechanisms underlying cataract formation and facilitating genetic counseling and early diagnosis for congenital cataract patients.

Fibroblast growth factor-induced lens fiber cell elongation is driven by the stepwise activity of Rho and Rac

The spheroidal shape of the eye lens is crucial for precise light focusing onto the retina. This shape is determined by concentrically aligned, convexly elongated lens fiber cells along the anterior and posterior axis of the lens. Upon differentiation at the lens equator, the fiber cells increase in height as their apical and basal tips migrate towards the anterior and posterior poles, respectively. The forces driving this elongation and migration remain unclear. We found that, in the mouse lens, membrane protrusions or lamellipodia are observed only in the maturing fibers undergoing cell curve conversion, indicating that lamellipodium formation is not the primary driver of earlier fiber migration. We demonstrated that elevated levels of fibroblast growth factor (FGF) suppressed the extension of Rac-dependent protrusions, suggesting changes in the activity of FGF controlling Rac activity, switching to lamellipodium-driven migration. Inhibitors of ROCK, myosin and actin reduced the height of both early and later fibers, indicating that elongation of these fibers relies on actomyosin contractility. Consistent with this, active RhoA was detected throughout these fibers. Given that FGF promotes fiber elongation, we propose that it does so through regulation of Rho activity.

TOB1 and TOB2 mark distinct RNA processing granules in differentiating lens fiber cells

Differentiation of lens fiber cells involves a complex interplay of signals from growth factors together with tightly regulated gene expression via transcriptional and post-transcriptional regulators. Various studies have demonstrated that RNA-binding proteins, functioning in ribonucleoprotein granules, have important roles in regulating post-transcriptional expression during lens development. In this study, we examined the expression and localization of two members of the BTG/TOB family of RNA-binding proteins, TOB1 and TOB2, in the developing lens and examined the phenotype of mice that lack Tob1. By RT-PCR, both Tob1 and Tob2 mRNA were detected in epithelial and fiber cells of embryonic and postnatal murine lenses. In situ hybridization showed Tob1 and Tob2 mRNA were most intensely expressed in the early differentiating fibers, with weaker expression in anterior epithelial cells, and both appeared to be downregulated in the germinative zone of E15.5 lenses. TOB1 protein was detected from E11.5 to E16.5 and was predominantly detected in large cytoplasmic puncta in early differentiating fiber cells, often co-localizing with the P-body marker, DCP2. Occasional nuclear puncta were also observed. By contrast, TOB2 was detected in a series of interconnected peri-nuclear granules, in later differentiating fiber cells of the inner cortex. TOB2 did not appear to co-localize with DCP2 but did partially co-localize with an early stress granule marker (EIF3B). These data suggest that TOB1 and TOB2 are involved with different aspects of the mRNA processing cycle in lens fiber cells. In vitro experiments using rat lens epithelial explants treated with or without a fiber differentiating dose of FGF2 showed that both TOB1 and TOB2 were up-regulated during FGF-induced differentiation. In differentiating explants, TOB1 also co-localized with DCP2 in large cytoplasmic granules. Analyses of Tob1-/- mice revealed relatively normal lens morphology but a subtle defect in cell cycle arrest of some cells at the equator and in the lens fiber mass of E13.5 embryos. Overall, these findings suggest that TOB proteins play distinct regulatory roles in RNA processing during lens fiber differentiation.

Integrated single-cell multiomics uncovers foundational regulatory mechanisms of lens development and pathology

Ocular lens development entails epithelial to fiber cell differentiation, defects in which cause congenital cataracts. We report the first single-cell multiomic atlas of lens development, leveraging snRNA-seq, snATAC-seq and CUT&RUN-seq to discover previously unreported mechanisms of cell fate determination and cataract-linked regulatory networks. A comprehensive profile of cis- and trans-regulatory interactions, including for the cataract-linked transcription factor MAF, is established across a temporal trajectory of fiber cell differentiation. Furthermore, we identify an epigenetic paradigm of cellular differentiation, defined by progressive loss of the H3K27 methylation writer Polycomb repressive complex 2 (PRC2). PRC2 localizes to heterochromatin domains across master-regulator transcription factor gene bodies, suggesting it safeguards epithelial cell fate. Moreover, we demonstrate that FGF hyper-stimulation in vivo leads to MAF network activation and the emergence of novel lens cell states. Collectively, these data depict a comprehensive portrait of lens fiber cell differentiation, while defining regulatory effectors of cell identity and cataract formation.

Fibroblast Growth Factor-induced lens fiber cell elongation is driven by the stepwise activity of Rho and Rac

The spheroidal shape of the eye lens is critical for precise light focusing onto the retina. This shape is determined by concentrically aligned, convexly elongated lens fiber cells along the anterior and posterior axis of the lens. Upon differentiation at the lens equator, the fiber cells increase in height as their apical and basal tips migrate towards the anterior and posterior poles, respectively. The forces driving this elongation and migration remain unclear. We found that membrane protrusions or lamellipodia are observed only in the maturing fibers undergoing cell curve conversion, indicating lamellipodium is not the primary driver of earlier fiber migration. We demonstrated that elevated levels of fibroblast growth factor (FGF) suppressed the extension of Rac-dependent protrusions, suggesting changes in the activity of FGF controling Rac activity, switching to lamellipodium-driven migration. Inhibitors of ROCK, myosin, and actin reduced the height of both early and later fibers, indicating elongation of these fibers relies on actomyosin contractility. Consistently, active RhoA was detected throughout these fibers. Given that FGF promotes fiber elongation, we propose it to do so through regulation of Rho activity.

Integrated single-cell multiomics uncovers foundational regulatory mechanisms of lens development and pathology

Ocular lens development entails epithelial to fiber cell differentiation, defects in which cause congenital cataract. We report the first single-cell multiomic atlas of lens development, leveraging snRNA-seq, snATAC-seq, and CUT&RUN-seq to discover novel mechanisms of cell fate determination and cataract-linked regulatory networks. A comprehensive profile of cis- and trans-regulatory interactions, including for the cataract-linked transcription factor MAF, is established across a temporal trajectory of fiber cell differentiation. Further, we divulge a conserved epigenetic paradigm of cellular differentiation, defined by progressive loss of H3K27 methylation writer Polycomb repressive complex 2 (PRC2). PRC2 localizes to heterochromatin domains across master-regulator transcription factor gene bodies, suggesting it safeguards epithelial cell fate. Moreover, we demonstrate that FGF hyper-stimulation in vivo leads to MAF network activation and the emergence of novel lens cell states. Collectively, these data depict a comprehensive portrait of lens fiber cell differentiation, while defining regulatory effectors of cell identity and cataract formation.

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.

Role of FGF10/FGFR2b Signaling in Homeostasis and Regeneration of Adult Lacrimal Gland and Corneal Epithelium Proliferation

Purpose

Fibroblast growth factor 10 (FGF10) is involved in eye, meibomian, and lacrimal gland (LG) development, but its function in adult eye structures remains unknown. This study aimed to characterize the role of FGF10 in homeostasis and regeneration of adult LG and corneal epithelium proliferation.

Methods

Quantitative reverse transcription PCR was used for analysis of FGF10 expression in both early postnatal and adult mouse LG, and RNA sequencing was used to analyze gene expression during LG inflammation. FGF10 was injected into the LG of two mouse models of Sjögren's syndrome and healthy controls. Flow cytometry, BrdU cell proliferation assay, immunostaining, and hematoxylin and eosin staining were used to evaluate the effects of FGF10 injection on inflammation and cell proliferation in vivo. Mouse and human epithelial cell cultures were treated with FGF10 in vitro, and cell viability was assessed using WST-8 and adenosine triphosphate (ATP) quantification assays.

Results

The level of Fgf10 mRNA expression was lower in adult LG compared to early postnatal LG and was downregulated in chronic inflammation. FGF10 injection into diseased LGs significantly increased cell proliferation and decreased the number of B cells. Mouse and human corneal epithelial cell cultures treated with FGF10 showed significantly higher cell viability and greater cell proliferation.

Conclusions

FGF10 appears to promote regeneration in damaged adult LGs. These findings have therapeutic potential for developing new treatments for dry eye disease targeting the ability of the cornea and LG to regenerate.

Generation of Lens Progenitor Cells and Lentoid Bodies from Pluripotent Stem Cells: Novel Tools for Human Lens Development and Ocular Disease Etiology

In vitro differentiation of human pluripotent stem cells (hPSCs) into specialized tissues and organs represents a powerful approach to gain insight into those cellular and molecular mechanisms regulating human development. Although normal embryonic eye development is a complex process, generation of ocular organoids and specific ocular tissues from pluripotent stem cells has provided invaluable insights into the formation of lineage-committed progenitor cell populations, signal transduction pathways, and self-organization principles. This review provides a comprehensive summary of recent advances in generation of adenohypophyseal, olfactory, and lens placodes, lens progenitor cells and three-dimensional (3D) primitive lenses, "lentoid bodies", and "micro-lenses". These cells are produced alone or "community-grown" with other ocular tissues. Lentoid bodies/micro-lenses generated from human patients carrying mutations in crystallin genes demonstrate proof-of-principle that these cells are suitable for mechanistic studies of cataractogenesis. Taken together, current and emerging advanced in vitro differentiation methods pave the road to understand molecular mechanisms of cataract formation caused by the entire spectrum of mutations in DNA-binding regulatory genes, such as PAX6, SOX2, FOXE3, MAF, PITX3, and HSF4, individual crystallins, and other genes such as BFSP1, BFSP2, EPHA2, GJA3, GJA8, LIM2, MIP, and TDRD7 represented in human cataract patients.

A possible connection between reactive oxygen species and the unfolded protein response in lens development: From insight to foresight

The lens is a relatively special and simple organ. It has become an ideal model to study the common developmental characteristics among different organic systems. Lens development is a complex process influenced by numerous factors, including signals from the intracellular and extracellular environment. Reactive oxygen species (ROS) are a group of highly reactive and oxygen-containing molecules that can cause endoplasmic reticulum stress in lens cells. As an adaptive response to ER stress, lens cells initiate the unfolded protein response (UPR) to maintain normal protein synthesis by selectively increasing/decreasing protein synthesis and increasing the degradation of misfolded proteins. Generally, the UPR signaling pathways have been well characterized in the context of many pathological conditions. However, recent studies have also confirmed that all three UPR signaling pathways participate in a variety of developmental processes, including those of the lens. In this review, we first briefly summarize the three stages of lens development and present the basic profiles of ROS and the UPR. We then discuss the interconnections between lens development and these two mechanisms. Additionally, the potential adoption of human pluripotent stem-cell-based lentoids in lens development research is proposed to provide a novel perspective on future developmental studies.

Jack of all trades, master of each: the diversity of fibroblast growth factor signalling in eye development

A central question in development biology is how a limited set of signalling pathways can instruct unlimited diversity of multicellular organisms. In this review, we use three ocular tissues as models of increasing complexity to present the astounding versatility of fibroblast growth factor (FGF) signalling. In the lacrimal gland, we highlight the specificity of FGF signalling in a one-dimensional model of budding morphogenesis. In the lens, we showcase the dynamics of FGF signalling in altering functional outcomes in a two-dimensional space. In the retina, we present the prolific utilization of FGF signalling from three-dimensional development to homeostasis. These examples not only shed light on the cellular basis for the perfection and complexity of ocular development, but also serve as paradigms for the diversity of FGF signalling.

Berbamine Inhibits Cell Proliferation and Migration and Induces Cell Death of Lung Cancer Cells via Regulating c-Maf, PI3K/Akt, and MDM2-P53 Pathways

Berbamine (BBM) is a natural product isolated from Berberis amurensis Rupr. We investigated the influence of BBM on the cell viability, proliferation, and migration of lung cancer cells and explored the possible mechanisms. The cell viability and proliferation of lung cancer cells were evaluated by MTT assay, EdU assay, and colony formation assay. Migration and invasion abilities of cancer cells were determined through wound scratch assay and Transwell assay. Cell death was evaluated by cell death staining assay and ELISA. The expressions of proteins were evaluated using western blot assay. A xenograft mouse model derived from non-small-cell lung cancer cells was used to detect the effect of BBM on tumor growth and metastasis in vivo. Both colony formation and EdU assays results revealed that BBM (10 μM) significantly inhibited the proliferation of A549 cells (P < 0.001). BBM (10 μM) also significantly inhibited the migration and invasion ability of cancer cells in wound scratch and Transwell assays. Trypan blue assay and ELISA revealed that BBM (20 μM) significantly induced cell death of A549 cells. In xenograft mouse models, the tumor volume was significantly smaller in mice treated with BBM (20 mg/kg). The western blotting assay showed that BBM inhibited the PI3K/Akt and MDM2-p53 signaling pathways, and BBM downregulated the expression of c-Maf. Our results show that BBM inhibits proliferation and metastasis and induces cell death of lung cancer cells in vitro and in vivo. These effects may be achieved by BBM reducing the expression of c-Maf and regulating the PI3K/Akt and MDM2-p53 pathways.

Crystallin gene expression: Insights from studies of transcriptional bursting

Cellular differentiation is marked by temporally and spatially regulated gene expression. The ocular lens is one of the most powerful mammalian model system since it is composed from only two cell subtypes, called lens epithelial and fiber cells. Lens epithelial cells differentiate into fiber cells through a series of spatially and temporally orchestrated processes, including massive production of crystallins, cellular elongation and the coordinated degradation of nuclei and other organelles. Studies of transcriptional and posttranscriptional gene regulatory mechanisms in lens provide a wide range of opportunities to understand global molecular mechanisms of gene expression as steady-state levels of crystallin mRNAs reach very high levels comparable to globin genes in erythrocytes. Importantly, dysregulation of crystallin gene expression results in lens structural abnormalities and cataracts. The mRNA life cycle is comprised of multiple stages, including transcription, splicing, nuclear export into cytoplasm, stabilization, localization, translation and ultimate decay. In recent years, development of modern mRNA detection methods with single molecule and single cell resolution enabled transformative studies to visualize the mRNA life cycle to generate novel insights into the sequential regulatory mechanisms of gene expression during embryogenesis. This review is focused on recent major advancements in studies of transcriptional bursting in differentiating lens fiber cells, analysis of nascent mRNA expression from bi-directional promoters, transient nuclear accumulation of specific mRNAs, condensation of chromatin prior lens fiber cell denucleation, and outlines future studies to probe the interactions of individual mRNAs with specific RNA-binding proteins (RBPs) in the cytoplasm and regulation of translation and mRNA decay.

Aberrant TGF-β1 signaling activation by MAF underlies pathological lens growth in high myopia

High myopia is a leading cause of blindness worldwide. Myopia progression may lead to pathological changes of lens and affect the outcome of lens surgery, but the underlying mechanism remains unclear. Here, we find an increased lens size in highly myopic eyes associated with up-regulation of β/γ-crystallin expressions. Similar findings are replicated in two independent mouse models of high myopia. Mechanistic studies show that the transcription factor MAF plays an essential role in up-regulating β/γ-crystallins in high myopia, by direct activation of the crystallin gene promoters and by activation of TGF-β1-Smad signaling. Our results establish lens morphological and molecular changes as a characteristic feature of high myopia, and point to the dysregulation of the MAF-TGF-β1-crystallin axis as an underlying mechanism, providing an insight for therapeutic interventions.

High myopia is associated with lens changes, but the underlying mechanisms are unclear. Here, the authors show increased equatorial diameter of the lens in subjects affected by high myopia, and find that these changes are associated with an increase in crystallin expression driven by the transcription factor MAF and TGF-β1 signaling.

IL-10 production by ILC2s requires Blimp-1 and cMaf, modulates cellular metabolism, and ameliorates airway hyperreactivity

BACKGROUND

Group 2 innate lymphoid cells (ILC2s) are the dominant innate lymphoid cell population in the lungs at steady state, and their release of type 2 cytokines is a central driver in responding eosinophil infiltration and increased airway hyperreactivity. Our laboratory has identified a unique subset of ILC2s in the lungs that actively produce IL-10 (ILC210s).

OBJECTIVE

Our aim was to characterize the effector functions of ILC210s in the development and pathology of allergic asthma.

METHODS

IL-4-stimulated ILC210s were isolated to evaluate cytokine secretion, transcription factor signaling, metabolic dependence, and effector functions in vitro. ILC210s were also adoptively transferred into Rag2-/-γc-/- mice, which were then challenged with IL-33 and assessed for airway hyperreactivity and lung inflammation.

RESULTS

We have determined that the transcription factors cMaf and Blimp-1 regulate IL-10 expression in ILC210s. Strikingly, our results demonstrate that ILC210s can utilize both autocrine and paracrine signaling to suppress proinflammatory ILC2 effector functions in vitro. Further, this subset dampens airway hyperreactivity and significantly reduces lung inflammation in vivo. Interestingly, ILC210s demonstrated a metabolic dependency on the glycolytic pathway for IL-10 production, shifting from the fatty acid oxidation pathway conventionally utilized for proinflammatory effector functions.

CONCLUSION

These findings provide an important and previously unrecognized role of ILC210s in diseases associated with ILC2s such as allergic lung inflammation and asthma. They also provide new insights into the metabolism dependency of proinflammatory and anti-inflammatory ILC2 phenotypes.

On the Nature of Murine Radiation-Induced Subcapsular Cataracts: Optical Coherence Tomography-Based Fine Classification, In Vivo Dynamics and Impact on Visual Acuity

Ionizing radiation is widely known to induce various kinds of lens cataracts, of which posterior subcapsular cataracts (PSCs) have the highest prevalence. Despite some studies regarding the epidemiology and biology of radiation-induced PSCs, the mechanism underscoring the formation of this type of lesions and their dose dependency remain uncertain. Within the current study, our team investigated the in vivo characteristics of PSCs in B6C3F1 mice (F1-hybrids of BL6 × C3H) that received 0.5-2 Gy γ-ray irradiation after postnatal day 70. For purposes of assessing lenticular damages, spectral domain optical coherence tomography was utilized, and the visual acuity of the mice was measured to analyze their levels of visual impairment, and histological sections were then prepared in to characterize in vivo phenotypes. Three varying in vivo phenotype anterior and posterior lesions were thus revealed and correlated with the applied doses to understand their marginal influence on the visual acuity of the studied mice. Histological data indicated no significantly increased odds ratios for PSCs below a dose of 1 Gy at the end of the observation time. Furthermore, our team demonstrated that when the frequencies of the posterior and anterior lesions were calculated at early time points, their responses were in accordance with a deterministic model, whereas at later time points, their responses were better described via a stochastic model. The current study will aid in honing the current understanding of radiation-induced cataract formation and contributes greatly to addressing the fundamental questions of lens dose response within the field of radiation biology.

Identification and characterization of a novel adiponectin receptor agonist adipo anti-inflammation agonist and its anti-inflammatory effects in vitro and in vivo

BACKGROUND AND PURPOSE

Adiponectin (APN) is an adipokine secreted from adipocytes that binds to APN receptors AdipoR1 and AdipoR2 and exerts an anti-inflammatory response through mechanisms not fully understood. There is a need to develop small molecules that activate AdipoR1 and AdipoR2 and to be used to inhibit the inflammatory response in lipopolysaccharide (LPS)-induced endotoxemia and other inflammatory disorders.

EXPERIMENTAL APPROACH

We designed 10 new structural analogues of an AdipoR agonist, AdipoRon (APR), and assessed their anti-inflammatory properties. Bone marrow-derived macrophages (BMMs) and peritoneal macrophages (PEMs) were isolated from mice. Levels of pro-inflammatory cytokines were measured by reverse transcription and real-time quantitative polymerase chain reaction (qRT-PCR), enzyme-linked immunosorbent assay (ELISA) and microarray in LPS-induced endotoxemia mice and diet-induced obesity (DIO) mice in which systemic inflammation prevails. Western blotting, immunohistochemistry (IHC), siRNA interference and immunoprecipitation were used to detect signalling pathways.

KEY RESULTS

A novel APN receptor agonist named adipo anti-inflammation agonist (AdipoAI) strongly suppresses inflammation in DIO and endotoxemia mice, as well as in cultured macrophages. We also found that AdipoAI attenuated the association of AdipoR1 and APPL1 via myeloid differentiation marker 88 (MyD88) signalling, thus inhibiting activation of nuclear factor kappa B (NF-κB), mitogen-activated protein kinase (MAPK) and c-Maf pathways and limiting the production of pro-inflammatory cytokines in LPS-induced macrophages.

CONCLUSION AND IMPLICATIONS

AdipoAI is a promising alternative therapeutic approach to APN and APR to suppress inflammation in LPS-induced endotoxemia and other inflammatory disorders via distinct signalling pathways.

The novel mutation P36R in LRP5L contributes to congenital membranous cataract via inhibition of laminin γ1 and c-MAF

PURPOSE

The present study investigated a pathogenic mutation and its mechanism on membranous cataract in a congenital membranous cataract family.

METHODS

An autosomal dominant four-generation Chinese congenital membranous cataract family was recruited and whole-exome sequencing was performed to screen for sequence variants. Candidate variants were validated using polymerase chain reaction and Sanger sequencing. Wild-type and mutant low-density lipoprotein receptor-related protein 5-like (LRP5L) plasmids were constructed and transfected into human lens epithelial cells (HLE B-3) and human anterior lens capsules. The cell lysates, nuclear and cytoplasmic proteins, and basement membrane components of HLE B-3 cells were harvested. LRP5L and laminin γ1 were knocked down in HLE B-3 cells using specific small-interfering RNA. The protein expression levels of LRP5L, laminin γ1, and c-MAF were detected using immunoblotting and immunofluorescence.

RESULTS

We identified a novel suspected pathogenic mutation in LRP5L (c.107C > G, p.P36R) in the congenital membranous cataract family. This mutation was absent in 300 normal controls and 300 age-related cataract patients. Bioinformatics analysis with PolyPhen-2 and SIFT suggested that LRP5L-P36R was pathogenic. LRP5L upregulated laminin γ1 expression in the cytoplasmic proteins of HLE B-3 cells and human anterior lens capsules, and LRP5L-P36R inhibited the effects of LRP5L. LRP5L upregulated c-MAF expression in the nucleus and cytoplasm of HLE B-3 cells, and LRP5L-P36R inhibited c-MAF expression via inhibition of laminin γ1.

CONCLUSION

Our study identified a novel gene, LRP5L, associated with congenital membranous cataract, and its mutant LRP5L-P36R contributed to membranous cataract development via inhibition of laminin γ1 and c-MAF.

Etv transcription factors functionally diverge from their upstream FGF signaling in lens development

The signal regulated transcription factors (SRTFs) control the ultimate transcriptional output of signaling pathways. Here, we examined a family of FGF-induced SRTFs - Etv1, Etv 4, and Etv 5 - in murine lens development. Contrary to FGF receptor mutants that displayed loss of ERK signaling and defective cell differentiation, Etv deficiency augmented ERK phosphorylation without disrupting the normal lens fiber gene expression. Instead, the transitional zone for lens differentiation was shifted anteriorly as a result of reduced Jag1-Notch signaling. We also showed that Etv proteins suppresses mTOR activity by promoting Tsc2 expression, which is necessary for the nuclei clearance in mature lens. These results revealed the functional divergence between Etv and FGF in lens development, demonstrating that these SRTFs can operate outside the confine of their upstream signaling.

Transcriptomic analysis and novel insights into lens fibre cell differentiation regulated by Gata3

Gata3 is a DNA-binding transcription factor involved in cellular differentiation in a variety of tissues including inner ear, hair follicle, kidney, mammary gland and T-cells. In a previous study in 2009, Maeda et al. (Dev. Dyn.238, 2280–2291; doi:10.1002/dvdy.22035) found that Gata3 mutants could be rescued from midgestational lethality by the expression of a Gata3 transgene in sympathoadrenal neuroendocrine cells. The rescued embryos clearly showed multiple defects in lens fibre cell differentiation. To determine whether these defects were truly due to the loss of Gata3 expression in the lens, we generated a lens-specific Gata3 loss-of-function model. Analogous to the previous findings, our Gata3 null embryos showed abnormal regulation of cell cycle exit during lens fibre cell differentiation, marked by reduction in the expression of the cyclin-dependent kinase inhibitors Cdkn1b/p27 and Cdkn1c/p57, and the retention of nuclei accompanied by downregulation of Dnase IIβ. Comparisons of transcriptomes between control and mutated lenses by RNA-Seq revealed dysregulation of lens-specific crystallin genes and intermediate filament protein Bfsp2. Both Cdkn1b/p27 and Cdkn1c/p57 loci are occupied in vivo by Gata3, as well as Prox1 and c-Jun, in lens chromatin. Collectively, our studies suggest that Gata3 regulates lens differentiation through the direct regulation of the Cdkn1b/p27and Cdkn1c/p57 expression, and the direct/or indirect transcriptional control of Bfsp2 and Dnase IIβ.

Molecular characterization of the human lens epithelium-derived cell line SRA01/04

Cataract-associated gene discovery in human and animal models have informed on key aspects of human lens development, homeostasis and pathology. Additionally, in vitro models such as the culture of permanent human lens epithelium-derived cell lines (LECs) have also been utilized to understand the molecular biology of lens cells. However, these resources remain uncharacterized, specifically regarding their global gene expression and suitability to model lens cell biology. Therefore, we sought to molecularly characterize gene expression in the human LEC, SRA01/04, which is commonly used in lens studies. We first performed short tandem repeat (STR) analysis and validated SRA01/04 LEC for its human origin, as recommended by the eye research community. Next, we used Illumina HumanHT-12 v3.0 Expression BeadChip arrays to gain insights into the global gene expression profile of SRA01/04. Comparative analysis of SRA01/04 microarray data was performed using other resources such as the lens expression database iSyTE (integrated Systems Tool for Eye gene discovery), the cataract gene database Cat-Map and the published lens literature. This analysis showed that SRA01/04 significantly expresses >40% of the top iSyTE lens-enriched genes (313 out of 749) across different developmental stages. Further, SRA01/04 also significantly expresses ~53% (168 out of 318) of cataract-associated genes in Cat-Map. We also performed comparative gene expression analysis between SRA01/04 cells and the previously validated mouse LEC 21EM15. To gain insight into whether SRA01/04 reflects epithelial or fiber cell characteristics, we compared its gene expression profile to previously reported differentially expressed genes in isolated mouse lens epithelial and fiber cells. This analysis suggests that SRA01/04 has reduced expression of several fiber cell-enriched genes. In agreement with these findings, cell culture analysis demonstrates that SRA01/04 has reduced potential to initiate spontaneous lentoid body formation compared to 21EM15 cells. Next, to independently validate SRA01/04 microarray gene expression, we subjected several candidate genes to RT-PCR and RT-qPCR assays. This analysis demonstrates that SRA01/04 supports expression of many key genes associated with lens development and cataract, including CRYAB, CRYBB2, CRYGS, DKK3, EPHA2, ETV5, GJA1, HSPB1, INPPL1, ITGB1, PAX6, PVRL3, SFRP1, SPARC, TDRD7, and VIM, among others, and therefore can be relevant for understanding the mechanistic basis of these factors. At the same time, SRA01/04 cells do not exhibit robust expression of several genes known to be important to lens biology and cataract such as ALDH1A1, COL4A6, CP, CRYBA4, FOXE3, HMX1, HSF4, MAF, MEIS1, PITX3, PRX, SIX3, and TRPM3, among many others. Therefore, the present study offers a rich transcript-level resource for case-by-case evaluation of the potential advantages and limitations of SRA01/04 cells prior to their use in downstream investigations. In sum, these data show that the human LEC, SRA01/04, exhibits lens epithelial cell-like character reflected in the expression of several lens-enriched and cataract-associated genes, and therefore can be considered as a useful in vitro resource when combined with in vivo studies to gain insight into specific aspects of human lens epithelial cells.

Profiling of chromatin accessibility and identification of general cis-regulatory mechanisms that control two ocular lens differentiation pathways

BACKGROUND

Promoters and enhancers are cis-regulatory DNA sequences that control specificity and quantity of transcription. Both are rich on clusters of cis-acting sites that interact with sequence-specific DNA-binding transcription factors (TFs). At the level of chromatin, these regions display increased nuclease sensitivity, reduced nucleosome density, including nucleosome-free regions, and specific combinations of posttranslational modifications of core histone proteins. Together, "open" and "closed" chromatins represent transcriptionally active and repressed states of individual genes, respectively. Cellular differentiation is marked by changes in local chromatin structure. Lens morphogenesis, regulated by TF Pax6, includes differentiation of epithelial precursor cells into lens fibers in parallel with differentiation of epithelial precursors into the mature lens epithelium.

RESULTS

Using ATAC-seq, we investigated dynamics of chromatin changes during mouse lens fibers and epithelium differentiation. Tissue-specific features of these processes are demonstrated via comparative studies of embryonic stem cells, forebrain, and liver chromatins. Unbiased analysis reveals cis-regulatory logic of lens differentiation through known (e.g., AP-1, Ets, Hsf4, Maf, and Pax6 sites) and novel (e.g., CTCF, Tead, and NF1) motifs. Twenty-six DNA-binding TFs, recognizing these cis-motifs, are markedly up-regulated in differentiating lens fibers. As specific examples, our ATAC-seq data uncovered both the regulatory regions and TF binding motifs in Foxe3, Prox1, and Mip loci that are consistent with previous, though incomplete, experimental data. A cross-examination of Pax6 binding with ATAC-seq data demonstrated that Pax6 bound to both open (H3K27ac and P300-enriched) and closed chromatin domains in lens and forebrain.

CONCLUSIONS

Our study has generated the first lens chromatin accessibility maps that support a general model of stage-specific chromatin changes associated with transcriptional activities of batteries of genes required for lens fiber cell formation. Analysis of active (or open) promoters and enhancers reveals important cis-DNA motifs that establish the molecular foundation for temporally and spatially regulated gene expression in lens. Together, our data and models open new avenues for the field to conduct mechanistic studies of transcriptional control regions, reconstruction of gene regulatory networks that govern lens morphogenesis, and identification of cataract-causing mutations in noncoding sequences.

Eye organogenesis: A hierarchical view of ocular development

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

Promoter-enhancer looping and shadow enhancers of the mouse αA-crystallin locus

Gene regulation by enhancers is important for precise temporal and spatial gene expression. Enhancers can drive gene expression regardless of their location, orientation or distance from the promoter. Changes in chromatin conformation and chromatin looping occur to bring the promoter and enhancers into close proximity. αA-crystallin ranks among one of the most abundantly expressed genes and proteins in the mammalian lens. The αA-crystallin locus is characterized by a 16 kb chromatin domain marked by two distal enhancers, 5′ DCR1 and 3′ DCR3. Here we used chromatin conformation capture (3C) analysis and transgenic approaches to analyze temporal control of the mouse αA-crystallin gene. We find that DCR1 is necessary, but not sufficient alone to drive expression at E10.5 in the mouse lens pit. Chromatin looping revealed interaction between the promoter and the region 3′ to DCR1, identifying a novel enhancer region in the αA-crystallin locus. We determined that this novel enhancer region, DCR1S, recapitulates the temporal control by DCR1. Acting as shadow enhancers, DCR1 and DCR1S are able to control expression in the lens vesicle at E11.5. It remains to be elucidated however, which region of the αA-crystallin locus is responsible for expression in the lens pit at E10.5.

Summary: The αA-crystallin ranks amongst the most highly expressed tissue-specific genes. It is an advantageous model system to probe both promoter-enhancer looping and to identify distal enhancers and their temporal/spatial activities.

Identification of Novel Gata3 Distal Enhancers Active in Mouse Embryonic Lens

BACKGROUND

The tissue-specific transcriptional programs during normal development require tight control by distal cis-regulatory elements, such as enhancers, with specific DNA sequences recognized by transcription factors, coactivators, and chromatin remodeling enzymes. Gata3 is a sequence-specific DNA-binding transcription factor that regulates formation of multiple tissues and organs, including inner ear, lens, mammary gland, T-cells, urogenital system, and thyroid gland. In the eye, Gata3 has a highly restricted expression domain in the posterior part of the lens vesicle; however, the underlying regulatory mechanisms are unknown.

RESULTS

Here we describe the identification of a novel bipartite Gata3 lens-specific enhancer located ∼18 kb upstream from its transcriptional start site. We also found that a 5-kb Gata3 promoter possesses low activity in the lens. The bipartite enhancer contains arrays of AP-1, Ets-, and Smad1/5-binding sites as well as binding sites for lens-associated DNA-binding factors. Transient transfection studies of the promoter with the bipartite enhancer showed enhanced activation by BMP4 and FGF2.

CONCLUSIONS

These studies identify a novel distal enhancer of Gata3 with high activity in lens and indicate that BMP and FGF signaling can up-regulate expression of Gata3 in differentiating lens fiber cells through the identified Gata3 enhancer and promoter elements. Developmental Dynamics 247:1186-1198, 2018. © 2018 The Authors. Developmental Dynamics published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.

Ubiquitin ligase COP1 coordinates transcriptional programs that control cell type specification in the developing mouse brain

The ubiquitin ligase CRL4^COP1/DET1 modifies specific transcription factor substrates with polyubiquitin so that they are degraded. However, the Ras–MEK–ERK signaling pathway can inactivate CRL4^COP1/DET1 and thereby promote the rapid accumulation of these transcription factors. Here we show that constitutive photomorphogenesis 1 (COP1) has a critical role in mouse brain development because its deletion from neural stem cells stabilizes the transcription factors c-JUN, ETV1, ETV4, and ETV5, leading to perturbation of normal gene expression patterns; anatomic anomalies in cerebral cortex, hippocampus, and cerebellum; and perinatal lethality.

The E3 ubiquitin ligase CRL4^COP1/DET1 is active in the absence of ERK signaling, modifying the transcription factors ETV1, ETV4, ETV5, and c-JUN with polyubiquitin that targets them for proteasomal degradation. Here we show that this posttranslational regulatory mechanism is active in neurons, with ETV5 and c-JUN accumulating within minutes of ERK activation. Mice with constitutive photomorphogenesis 1 (Cop1) deleted in neural stem cells showed abnormally elevated expression of ETV1, ETV4, ETV5, and c-JUN in the developing brain and spinal cord. Expression of c-JUN target genes Vimentin and Gfap was increased, whereas ETV5 and c-JUN both contributed to an expanded number of cells expressing genes associated with gliogenesis, including Olig1, Olig2, and Sox10. The mice had subtle morphological abnormalities in the cerebral cortex, hippocampus, and cerebellum by embryonic day 18 and died soon after birth. Elevated c-JUN, ETV5, and ETV1 contributed to the perinatal lethality, as several Cop1-deficient mice also lacking c-Jun and Etv5, or lacking Etv5 and heterozygous for Etv1, were viable.

A comprehensive spatial-temporal transcriptomic analysis of differentiating nascent mouse lens epithelial and fiber cells

Elucidation of both the molecular composition and organization of the ocular lens is a prerequisite to understand its development, function, pathology, regenerative capacity, as well as to model lens development and disease using in vitro differentiation of pluripotent stem cells. Lens is comprised of the anterior lens epithelium and posterior lens fibers, which form the bulk of the lens. Lens fibers differentiate from lens epithelial cells through cell cycle exit-coupled differentiation that includes cellular elongation, accumulation of crystallins, cytoskeleton and membrane remodeling, and degradation of organelles within the central region of the lens. Here, we profiled spatiotemporal expression dynamics of both mRNAs and non-coding RNAs from microdissected mouse nascent lens epithelium and lens fibers at four developmental time points (embryonic [E] day 14.5, E16.5, E18.5, and P0.5) by RNA-seq. During this critical time window, multiple complex biosynthetic and catabolic processes generate the molecular and structural foundation for lens transparency. Throughout this developmental window, 3544 and 3518 genes show consistently and significantly greater expression in the nascent lens epithelium and fibers, respectively. Comprehensive data analysis confirmed major roles of FGF-MAPK, Wnt/β-catenin, PI3K/AKT, TGF-β, and BMP signaling pathways and revealed significant novel contributions of mTOR, EIF2, EIF4, and p70S6K signaling in lens formation. Unbiased motif analysis within promoter regions of these genes with consistent expression changes between epithelium and fiber cells revealed an enrichment for both established (e.g. E2Fs, Etv5, Hsf4, c-Maf, MafG, MafK, N-Myc, and Pax6) transcription factors and a number of novel regulators of lens formation, such as Arntl2, Dmrta2, Stat5a, Stat5b, and Tulp3. In conclusion, the present RNA-seq data serves as a comprehensive reference resource for deciphering molecular principles of normal mammalian lens differentiation, mapping a full spectrum of signaling pathways and DNA-binding transcription factors operating in both lens compartments, and predicting novel pathways required to establish lens transparency.

Non-invasive in vivo quantification of the developing optical properties and graded index of the embryonic eye lens using SPIM

Graded refractive index lenses are inherent to advanced visual systems in animals. By understanding their formation and local optical properties, significant potential for improved ocular healthcare may be realized. We report a novel technique measuring the developing optical power of the eye lens, in a living animal, by exploiting the orthogonal imaging modality of a selective plane illumination microscope (SPIM). We have quantified the maturation of the lenticular refractive index at three different visible wavelengths using a combined imaging and ray tracing approach. We demonstrate that the method can be used with transgenic and vital dye labeling as well as with both fixed and living animals. Using a key eye lens morphogen and its inhibitor, we have measured their effects both on lens size and on refractive index. Our technique provides insights into the mechanisms involved in the development of this natural graded index micro-lens and its associated optical properties.

The zebrafish as a model system for analyzing mammalian and native α-crystallin promoter function

Previous studies have used the zebrafish to investigate the biology of lens crystallin proteins and their roles in development and disease. However, little is known about zebrafish α-crystallin promoter function, how it compares to that of mammals, or whether mammalian α-crystallin promoter activity can be assessed using zebrafish embryos. We injected a variety of α-crystallin promoter fragments from each species combined with the coding sequence for green fluorescent protein (GFP) into zebrafish zygotes to determine the resulting spatiotemporal expression patterns in the developing embryo. We also measured mRNA levels and protein abundance for all three zebrafish α-crystallins. Our data showed that mouse and zebrafish αA-crystallin promoters generated similar GFP expression in the lens, but with earlier onset when using mouse promoters. Expression was also found in notochord and skeletal muscle in a smaller percentage of embryos. Mouse αB-crystallin promoter fragments drove GFP expression primarily in zebrafish skeletal muscle, with less common expression in notochord, lens, heart and in extraocular regions of the eye. A short fragment containing only a lens-specific enhancer region increased lens and notochord GFP expression while decreasing muscle expression, suggesting that the influence of mouse promoter control regions carries over into zebrafish embryos. The two paralogous zebrafish αB-crystallin promoters produced subtly different expression profiles, with the aBa promoter driving expression equally in notochord and skeletal muscle while the αBb promoter resulted primarily in skeletal muscle expression. Messenger RNA for zebrafish αA increased between 1 and 2 days post fertilization (dpf), αBa increased between 4 and 5 dpf, but αBb remained at baseline levels through 5 dpf. Parallel reaction monitoring (PRM) mass spectrometry was used to detect αA, aBa, and αBb peptides in digests of zebrafish embryos. In whole embryos, αA-crystallin was first detected by 2 dpf, peaked in abundance by 4–5 dpf, and was localized to the eye. αBa was detected in whole embryo at nearly constant levels from 1–6 dpf, was also localized primarily to the eye, and its abundance in extraocular tissues decreased from 4–7 dpf. In contrast, due to its low abundance, no αBb protein could be detected in whole embryo, or dissected eye and extraocular tissues. Our results show that mammalian α-crystallin promoters can be efficiently screened in zebrafish embryos and that their controlling regions are well conserved. An ontogenetic shift in zebrafish aBa-crystallin promoter activity provides an interesting system for examining the evolution and control of tissue specificity. Future studies that combine these promoter based approaches with the expanding ability to engineer the zebrafish genome via techniques such as CRISPR/Cas9 will allow the manipulation of protein expression to test hypotheses about lens crystallin function and its relation to lens biology and disease.

Signaling and Gene Regulatory Networks in Mammalian Lens Development

Ocular lens development represents an advantageous system in which to study regulatory mechanisms governing cell fate decisions, extracellular signaling, cell and tissue organization, and the underlying gene regulatory networks. Spatiotemporally regulated domains of BMP, FGF, and other signaling molecules in late gastrula-early neurula stage embryos generate the border region between the neural plate and non-neural ectoderm from which multiple cell types, including lens progenitor cells, emerge and undergo initial tissue formation. Extracellular signaling and DNA-binding transcription factors govern lens and optic cup morphogenesis. Pax6, c-Maf, Hsf4, Prox1, Sox1, and a few additional factors regulate the expression of the lens structural proteins, the crystallins. Extensive crosstalk between a diverse array of signaling pathways controls the complexity and order of lens morphogenetic processes and lens transparency.

β1-Integrin Deletion From the Lens Activates Cellular Stress Responses Leading to Apoptosis and Fibrosis

Purpose

Previous research showed that the absence of β1-integrin from the mouse lens after embryonic day (E) 13.5 (β1MLR10) leads to the perinatal apoptosis of lens epithelial cells (LECs) resulting in severe microphthalmia. This study focuses on elucidating the molecular connections between β1-integrin deletion and this phenotype.

Methods

RNA sequencing was performed to identify differentially regulated genes (DRGs) in β1MLR10 lenses at E15.5. By using bioinformatics analysis and literature searching, Egr1 (early growth response 1) was selected for further study. The activation status of certain signaling pathways (focal adhesion kinase [FAK]/Erk, TGF-β, and Akt signaling) was studied via Western blot and immunohistochemistry. Mice lacking both β1-integrin and Egr1 genes from the lenses were created (β1MLR10/Egr1-/-) to study their relationship.

Results

RNA sequencing identified 120 DRGs that include candidates involved in the cellular stress response, fibrosis, and/or apoptosis. Egr1 was investigated in detail, as it mediates cellular stress responses in various cell types, and is recognized as an upstream regulator of numerous other β1MLR10 lens DRGs. In β1MLR10 mice, Egr1 levels are elevated shortly after β1-integrin loss from the lens. Further, pErk1/2 and pAkt are elevated in β1MLR10 LECs, thus providing the potential signaling mechanism that causes Egr1 upregulation in the mutant. Indeed, deletion of Egr1 from β1MLR10 lenses partially rescues the microphthalmia phenotype.

Conclusions

β1-integrin regulates the appropriate levels of Erk1/2 and Akt phosphorylation in LECs, whereas its deficiency results in the overexpression of Egr1, culminating in reduced cell survival. These findings provide insight into the molecular mechanism underlying the microphthalmia observed in β1MLR10 mice.

Capicua deficiency induces autoimmunity and promotes follicular helper T cell differentiation via derepression of ETV5

High-affinity antibody production through the germinal centre (GC) response is a pivotal process in adaptive immunity. Abnormal development of follicular helper T (T_FH) cells can induce the GC response to self-antigens, subsequently leading to autoimmunity. Here we show the transcriptional repressor Capicua/CIC maintains peripheral immune tolerance by suppressing aberrant activation of adaptive immunity. CIC deficiency induces excessive development of T_FH cells and GC responses in a T-cell-intrinsic manner. ETV5 expression is derepressed in Cic null T_FH cells and knockdown of Etv5 suppresses the enhanced T_FH cell differentiation in Cic-deficient CD4⁺ T cells, suggesting that Etv5 is a critical CIC target gene in T_FH cell differentiation. Furthermore, we identify Maf as a downstream target of the CIC-ETV5 axis in this process. These data demonstrate that CIC maintains T-cell homeostasis and negatively regulates T_FH cell development and autoimmunity.

β1-integrin controls cell fate specification in early lens development

Integrins are heterodimeric cell surface molecules that mediate cell-extracellular matrix (ECM) adhesion, ECM assembly, and regulation of both ECM and growth factor induced signaling. However, the developmental context of these diverse functions is not clear. Loss of β1-integrin from the lens vesicle (mouse E10.5) results in abnormal exit of anterior lens epithelial cells (LECs) from the cell cycle and their aberrant elongation toward the presumptive cornea by E12.5. These cells lose expression of LEC markers and initiate expression of the Maf (also known as c-Maf) and Prox1 transcription factors as well as other lens fiber cell markers. β1-integrin null LECs also upregulate the ERK, AKT and Smad1/5/8 phosphorylation indicative of BMP and FGF signaling. By E14.5, β1-integrin null lenses have undergone a complete conversion of all lens epithelial cells into fiber cells. These data suggest that shortly after lens vesicle closure, β1-integrin blocks inappropriate differentiation of the lens epithelium into fibers, potentially by inhibiting BMP and/or FGF receptor activation. Thus, β1-integrin has an important role in fine-tuning the response of the early lens to the gradient of growth factors that regulate lens fiber cell differentiation.

PAX6: 25th anniversary and more to learn

The DNA-binding transcription factor PAX6 was cloned 25 years ago by multiple teams pursuing identification of human and mouse eye disease causing genes, cloning vertebrate homologues of pattern-forming regulatory genes identified in Drosophila, or abundant eye-specific transcripts. Since its discovery in 1991, genetic, cellular, molecular and evolutionary studies on Pax6 mushroomed in the mid 1990s leading to the transformative thinking regarding the genetic program orchestrating both early and late stages of eye morphogenesis as well as the origin and evolution of diverse visual systems. Since Pax6 is also expressed outside of the eye, namely in the central nervous system and pancreas, a number of important insights into the development and function of these organs have been amassed. In most recent years, genome-wide technologies utilizing massively parallel DNA sequencing have begun to provide unbiased insights into the regulatory hierarchies of specification, determination and differentiation of ocular cells and neurogenesis in general. This review is focused on major advancements in studies on mammalian eye development driven by studies of Pax6 genes in model organisms and future challenges to harness the technology-driven opportunities to reconstruct, step-by-step, the transition from naïve ectoderm, neuroepithelium and periocular mesenchyme/neural crest cells into the three-dimensional architecture of the eye.

The molecular mechanisms underlying lens fiber elongation

Lens fiber cells are highly elongated cells with complex membrane morphologies that are critical for the transparency of the ocular lens. Investigations into the molecular mechanisms underlying lens fiber cell elongation were first reported in the 1960s, however, our understanding of the process is still poor nearly 50 years later. This review summarizes what is currently hypothesized about the regulation of lens fiber cell elongation along with the available experimental evidence, and how this information relates to what is known about the regulation of cell shape/elongation in other cell types, particularly neurons.

Lens Development and Crystallin Gene Expression

The eye and lens represent excellent models to understand embryonic development at cellular and molecular levels. Initial 3D formation of the eye depends on a reciprocal invagination of the lens placode/optic vesicle to form the eye primordium, i.e., the optic cup partially surrounding the lens vesicle. Subsequently, the anterior part of the lens vesicle gives rise to the lens epithelium, while the posterior cells of the lens vesicle differentiate into highly elongated lens fibers. Lens fiber differentiation involves cytoskeletal rearrangements, cellular elongation, accumulation of crystallin proteins, production of extracellular matrix for the lens capsule, and degradation of organelles. This chapter summarizes recent advances in lens development and provides insights into the regulatory mechanisms and differentiation at the level of chromatin structure and dynamics, the emerging field of noncoding RNAs, and novel strategies to fill the gaps in our understanding of lens development.