A Trio-RhoA-Shroom3 pathway is required for apical constriction and epithelial invagination

The RhoGEF protein Plekhg5 self-associates via its PH domain to regulate apical cell constriction

RhoGEFs are critical activators of Rho family small GTPases and regulate diverse biological processes, such as cell division and tissue morphogenesis. We reported previously that the RhoGEF gene plekhg5 controls apical constriction of bottle cells at the blastopore lip during Xenopus gastrulation, but the detailed mechanism of plekhg5 action is not understood in depth. In this study, we show that localization of Plekhg5 in the apical cortex depends on its N-terminal sequences and intact guanine nucleotide exchange activity, whereas the C-terminal sequences prevent ectopic localization of the protein to the basolateral compartment. We also reveal that Plekhg5 self-associates via its PH domain, and this interaction leads to functional rescue of two mutants that lack the N-terminal region and the guanine nucleotide exchange factor activity, respectively, in trans. A point mutation in the PH domain corresponding to a variant associated with human disease leads to loss of self-association and failure of the mutant to induce apical constriction. Taken together, our results suggest that PH-mediated self-association and N-terminal domain-mediated subcellular localization are both crucial for the function of Plekhg5 in inducing apical constriction.

Lens placode modulates extracellular matrix formation during early eye development

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

Dentate Gyrus Morphogenesis is Regulated by an Autism Risk Gene Trio Function in Granule Cells

Autism Spectrum Disorders (ASDs) are reported as a group of neurodevelopmental disorders. The structural changes of brain regions including the hippocampus were widely reported in autistic patients and mouse models with dysfunction of ASD risk genes, but the underlying mechanisms are not fully understood. Here, we report that deletion of Trio, a high-susceptibility gene of ASDs, causes a postnatal dentate gyrus (DG) hypoplasia with a zigzagged suprapyramidal blade, and the Trio-deficient mice display autism-like behaviors. The impaired morphogenesis of DG is mainly caused by disturbing the postnatal distribution of postmitotic granule cells (GCs), which further results in a migration deficit of neural progenitors. Furthermore, we reveal that Trio plays different roles in various excitatory neural cells by spatial transcriptomic sequencing, especially the role of regulating the migration of postmitotic GCs. In summary, our findings provide evidence of cellular mechanisms that Trio is involved in postnatal DG morphogenesis.

Effect of cryopreservation on Odc1 and RhoA genes expression in diapausing mouse blastocysts

The possibility of embryo cryopreservation is important for applying the genome resource banking (GRB) concept to those mammalian species that exhibit embryonal diapause in their early development. Odc1 encodes ODC1, which is a key enzyme in polyamine synthesis. RhoA is an essential part of Rho/ROCK system. Both Odc1 and RhoA play an important role in preimplantation embryo development. Studying these systems in mammalian species with obligate or experimentally designed embryonic diapause may provide insight into the molecular machinery underlying embryo dormancy and re-activation. The effect of cryopreservation procedures on the expression of the Odc1 and RhoA in diapausing embryos has not been properly studied yet. The purpose of this work is to address the possibility of cryopreservation diapausing embryos and to estimate the expression of the Odc1 and RhoA genes in diapausing and non-diapausing embryos before and after freeze-thaw procedures using ovariectomized progesterone treated mice as a model. Both diapausing and non-diapausing in vivo-derived embryos continued their development in vitro after freezing-thawing as evidenced by blastocoel re-expansion. Although cryopreservation dramatically decreased the expression of the Odc1 and RhoA genes in non-diapausing embryos, no such effects have been observed in diapausing embryos where these genes were already at the low level before freeze-thaw procedures. Future studies may attempt to facilitate the re-activation of diapausing embryos, for example frozen-thawed ones, specifically targeting Odc1 or Rho/ROCK system.

The Critical Role of the Shroom Family Proteins in Morphogenesis, Organogenesis and Disease

The Shroom (Shrm) family of actin-binding proteins has a unique and highly conserved Apx/Shrm Domain 2 (ASD2) motif. Shroom protein directs the subcellular localization of Rho-associated kinase (ROCK), which remodels the actomyosin cytoskeleton and changes cellular morphology via its ability to phosphorylate and activate non-muscle myosin II. Therefore, the Shrm-ROCK complex is critical for the cellular shape and the development of many tissues, including the neural tube, eye, intestines, heart, and vasculature system. Importantly, the structure and expression of Shrm proteins are also associated with neural tube defects, chronic kidney disease, metastasis of carcinoma, and X-link mental retardation. Therefore, a better understanding of Shrm-mediated signaling transduction pathways is essential for the development of new therapeutic strategies to minimize damage resulting in abnormal Shrm proteins. This paper provides a comprehensive overview of the various Shrm proteins and their roles in morphogenesis and disease.

Lens Placode Modulates Extracellular Matrix Formation During Early Eye Development

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

TRIOBP modulates β-catenin signaling by regulation of miR-29b in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal and devastating lung disease of unknown etiology, described as the result of multiple cycles of epithelial cell injury and fibroblast activation. Despite this impressive increase in understanding, a therapy that reverses this form of fibrosis remains elusive. In our previous study, we found that miR-29b has a therapeutic effect on pulmonary fibrosis. However, its anti-fibrotic mechanism is not yet clear. Recently, our study identified that F-Actin Binding Protein (TRIOBP) is one of the target genes of miR-29b and found that deficiency of TRIOBP increases resistance to lung fibrosis in vivo. TRIOBP knockdown inhibited the proliferation of epithelial cells and attenuated the activation of fibroblasts. In addition, deficiency of Trio Rho Guanine Nucleotide Exchange Factor (TRIO) in epithelial cells and fibroblasts decreases susceptibility to lung fibrosis. TRIOBP interacting with TRIO promoted abnormal epithelial-mesenchymal crosstalk and modulated the nucleocytoplasmic translocation of β-catenin. We concluded that the miR-29b‒TRIOBP-TRIO-β-catenin axis might be a key anti-fibrotic axis in IPF to regulate lung regeneration and fibrosis, which may provide a promising treatment strategy for lung fibrosis.

Eye Morphogenesis in Vertebrates

Proper eye structure is essential for visual function: Multiple essential eye tissues must take shape and assemble into a precise three-dimensional configuration. Accordingly, alterations to eye structure can lead to pathological conditions of visual impairment. Changes in eye shape can also be adaptive over evolutionary time. Eye structure is first established during development with the formation of the optic cup, which contains the neural retina, retinal pigment epithelium, and lens. This crucial yet deceptively simple hemispherical structure lays the foundation for all later elaborations of the eye. Building on descriptions of the embryonic eye that started with hand drawings and micrographs, the field is beginning to identify mechanisms driving dynamic changes in three-dimensional cell and tissue shape. A combination of molecular genetics, imaging, and pharmacological approaches is defining connections among transcription factors, signaling pathways, and the intracellular machinery governing the emergence of this crucial structure.

Minimal Kidney Disease Phenotype in Shroom3 Heterozygous Null Mice

Background

Shroom family member 3 (SHROOM3) encodes an actin-associated protein that regulates epithelial morphology during development. Several genome-wide association studies (GWAS) have identified genetic variances primarily in the 5' region of SHROOM3, associated with chronic kidney disease (CKD) and poor transplant outcomes. These genetic variants are associated with alterations in Shroom3 expression.

Objective

Characterize the phenotypic abnormalities associated with reduced Shroom3 expression in postnatal day 3-, 1-month and 3-month-old mice.

Methods

The Shroom3 protein expression pattern was determined by immunofluorescence. We generated Shroom3 heterozygous null mice (Shroom3Gt/+) and performed comparative analyses with wild type littermates based on somatic and kidney growth, gross renal anatomy, renal histology, renal function at postnatal day 3, 1 month, and 3 months.

Results

The Shroom3 protein expression localized to the apical regions of medullary and cortical tubular epithelium in postnatal wild type kidneys. Co-immunofluorescence studies confirmed protein expression localized to the apical side of the tubular epithelium in proximal convoluted tubules, distal convoluted tubules, and collecting ducts. While Shroom3 heterozygous null mice exhibited reduced Shroom3 protein expression, no differences in somatic and kidney growth were observed when compared to wild type mice. Although, rare cases of unilateral hypoplasia of the right kidney were observed at postnatal 1 month in Shroom3 heterozygotes. Yet renal histological analysis did not reveal any overt abnormalities in overall kidney structure or in glomerular and tubular organization in Shroom3 heterozygous null mice when compared to wild type mice. Analysis of the apical-basolateral orientation of the tubule epithelium demonstrated alterations in the proximal convoluted tubules and modest disorganization in the distal convoluted tubules at 3 months in Shroom3 heterozygotes. Additionally, these modest abnormalities were not accompanied by tubular injury or physiological defects in renal and cardiovascular function.

Conclusion

Taken together, our results describe a mild kidney disease phenotype in adult Shroom3 heterozygous null mice, suggesting that Shroom3 expression and function may be required for proper structure and maintenance of the various tubular epithelial parenchyma of the kidney.

The RhoGEF protein Plekhg5 regulates medioapical and junctional actomyosin dynamics of apical constriction during Xenopus gastrulation

Apical constriction results in apical surface reduction in epithelial cells and is a widely used mechanism for epithelial morphogenesis. Both medioapical and junctional actomyosin remodeling are involved in apical constriction, but the deployment of medial versus junctional actomyosin and their genetic regulation in vertebrate embryonic development have not been fully described. In this study, we investigate actomyosin dynamics and their regulation by the RhoGEF protein Plekhg5 in Xenopus bottle cells. Using live imaging and quantitative image analysis, we show that bottle cells assume different shapes, with rounding bottle cells constricting earlier in small clusters followed by fusiform bottle cells forming between the clusters. Both medioapical and junctional actomyosin signals increase as surface area decreases, though correlation of apical constriction with medioapical actomyosin localization appears to be stronger. F-actin bundles perpendicular to the apical surface form in constricted cells, which may correspond to microvilli previously observed in the apical membrane. Knockdown of plekhg5 disrupts medioapical and junctional actomyosin activity and apical constriction but does not affect initial F-actin dynamics. Taking the results together, our study reveals distinct cell morphologies, uncovers actomyosin behaviors, and demonstrates the crucial role of a RhoGEF protein in controlling actomyosin dynamics during apical constriction of bottle cells in Xenopus gastrulation.

Gastrulation morphogenesis in synthetic systems

Recent advances in pluripotent stem cell culture allow researchers to generate not only most embryonic cell types, but also morphologies of many embryonic structures, entirely in vitro. This recreation of embryonic form from naïve cells, known as synthetic morphogenesis, has important implications for both developmental biology and regenerative medicine. However, the capacity of stem cell-based models to recapitulate the morphogenetic cell behaviors that shape natural embryos remains unclear. In this review, we explore several examples of synthetic morphogenesis, with a focus on models of gastrulation and surrounding stages. By varying cell types, source species, and culture conditions, researchers have recreated aspects of primitive streak formation, emergence and elongation of the primary embryonic axis, neural tube closure, and more. Here, we describe cell behaviors within in vitro/ex vivo systems that mimic in vivo morphogenesis and highlight opportunities for more complete models of early development.

Structure and regulation of the myotonic dystrophy kinase-related Cdc42-binding kinase

Protein kinases of the dystonia myotonica protein kinase (DMPK) family are critical regulators of actomyosin contractility in cells. The DMPK kinase MRCK1 is required for the activation of myosin, leading to the development of cortical tension, apical constriction, and early gastrulation. Here, we present the structure, conformation, and membrane-binding properties of Caenorhabditis elegans MRCK1. MRCK1 forms a homodimer with N-terminal kinase domains, a parallel coiled coil of 55 nm, and a C-terminal tripartite module of C1, pleckstrin homology (PH), and citron homology (CNH) domains. We report the high-resolution structure of the membrane-binding C1-PH-CNH module of MRCK1 and, using high-throughput and conventional liposome-binding assays, determine its binding to specific phospholipids. We further characterize the interaction of the C-terminal CRIB motif with Cdc42. The length of the coiled-coil domain of DMPK kinases is remarkably conserved over millions of years of evolution, suggesting that they may function as molecular rulers to position kinase activity at a fixed distance from the membrane.

Curvature in Biological Systems: Its Quantification, Emergence, and Implications across the Scales

Surface curvature both emerges from, and influences the behavior of, living objects at length scales ranging from cell membranes to single cells to tissues and organs. The relevance of surface curvature in biology is supported by numerous experimental and theoretical investigations in recent years. In this review, first, a brief introduction to the key ideas of surface curvature in the context of biological systems is given and the challenges that arise when measuring surface curvature are discussed. Giving an overview of the emergence of curvature in biological systems, its significance at different length scales becomes apparent. On the other hand, summarizing current findings also shows that both single cells and entire cell sheets, tissues or organisms respond to curvature by modulating their shape and their migration behavior. Finally, the interplay between the distribution of morphogens or micro-organisms and the emergence of curvature across length scales is addressed with examples demonstrating these key mechanistic principles of morphogenesis. Overall, this review highlights that curved interfaces are not merely a passive by-product of the chemical, biological, and mechanical processes but that curvature acts also as a signal that co-determines these processes.

The RhoGAP-myosin Myo9b regulates ocular lens pit morphogenesis

BACKGROUND

During eye development the lens placode invaginates to form the lens pit. Further bending of lens epithelium and separation from ectoderm leads eventually to a spherical lens vesicle with enclosed extracellular fluid. Changes in epithelial morphology involve the actin cytoskeleton and its regulators. The myosin Myo9b is simultaneously an actin-based motor and Rho GTPase-activating protein that regulates actin cytoskeleton organization. Myo9b-deficient adult mice and embryos were analyzed for eye malformations and alterations in lens development.

RESULTS

Myo9b-deficient mice showed a high incidence of microphthalmia and cataracts with occasional blepharitis. Formation of the lens vesicle during embryonic lens development was disordered in virtually all embryos. Lens placode invagination was less deep and gave rise to a conical structure instead of a spherical pit. At later stages either no lens vesicle was formed or a significantly smaller one that was not enclosed by the optic cup. Expression of the cell fate marker Pax6 was not altered. Staining of adherens junctions and F-actin was most intense at the tip of conical invaginations, suggesting that mechanical forces are not properly coordinated between epithelial cells that form the pit.

CONCLUSIONS

Myo9b is a critical regulator of ocular lens vesicle morphogenesis during eye development.

Multifunctional role of GPCR signaling in epithelial tube formation

Epithelial tube formation requires Rho1-dependent actomyosin contractility to generate the cellular forces that drive cell shape changes and rearrangement. Rho1 signaling is activated by G-protein-coupled receptor (GPCR) signaling at the cell surface. During Drosophila embryonic salivary gland (SG) invagination, the GPCR ligand Folded gastrulation (Fog) activates Rho1 signaling to drive apical constriction. The SG receptor that transduces the Fog signal into Rho1-dependent myosin activation has not been identified. Here, we reveal that the Smog GPCR transduces Fog signal to regulate Rho kinase accumulation and myosin activation in the medioapical region of cells to control apical constriction during SG invagination. We also report on unexpected Fog-independent roles for Smog in maintaining epithelial integrity and organizing cortical actin. Our data support a model wherein Smog regulates distinct myosin pools and actin cytoskeleton in a ligand-dependent manner during epithelial tube formation.

Global analysis of cell behavior and protein dynamics reveals region-specific roles for Shroom3 and N-cadherin during neural tube closure

Failures of neural tube closure are common and serious birth defects, yet we have a poor understanding of the interaction of genetics and cell biology during neural tube closure. Additionally, mutations that cause neural tube defects (NTDs) tend to affect anterior or posterior regions of the neural tube but rarely both, indicating a regional specificity to NTD genetics. To better understand the regional specificity of cell behaviors during neural tube closure, we analyzed the dynamic localization of actin and N-cadherin via high-resolution tissue-level time-lapse microscopy during Xenopus neural tube closure. To investigate the regionality of gene function, we generated mosaic mutations in shroom3, a key regulator or neural tube closure. This new analytical approach elucidates several differences between cell behaviors during cranial/anterior and spinal/posterior neural tube closure, provides mechanistic insight into the function of shroom3, and demonstrates the ability of tissue-level imaging and analysis to generate cell biological mechanistic insights into neural tube closure.

Studying Kidney Diseases Using Organoid Models

The prevalence of chronic kidney disease (CKD) is rapidly increasing over the last few decades, owing to the global increase in diabetes, and cardiovascular diseases. Dialysis greatly compromises the life quality of patients, while demand for transplantable kidney cannot be met, underscoring the need to develop novel therapeutic approaches to stop or reverse CKD progression. Our understanding of kidney disease is primarily derived from studies using animal models and cell culture. While cross-species differences made it challenging to fully translate findings from animal models into clinical practice, primary patient cells quickly lose the original phenotypes during in vitro culture. Over the last decade, remarkable achievements have been made for generating 3-dimensional (3D) miniature organs (organoids) by exposing stem cells to culture conditions that mimic the signaling cues required for the development of a particular organ or tissue. 3D kidney organoids have been successfully generated from different types of source cells, including human pluripotent stem cells (hPSCs), adult/fetal renal tissues, and kidney cancer biopsy. Alongside gene editing tools, hPSC-derived kidney organoids are being harnessed to model genetic kidney diseases. In comparison, adult kidney-derived tubuloids and kidney cancer-derived tumoroids are still in their infancy. Herein, we first summarize the currently available kidney organoid models. Next, we discuss recent advances in kidney disease modelling using organoid models. Finally, we consider the major challenges that have hindered the application of kidney organoids in disease modelling and drug evaluation and propose prospective solutions.

Assays for Apical Constriction Using the Xenopus Model

Apical constriction refers to the active, actomyosin-driven process that reduces apical cell surface area in epithelial cells. Apical constriction is utilized in epithelial morphogenesis during embryonic development in multiple contexts, such as gastrulation, neural tube closure, and organogenesis. Defects in apical constriction can result in congenital birth defects, yet our understanding of the molecular control of apical constriction is relatively limited. To uncover new genetic regulators of apical constriction and gain mechanistic insight into the cell biology of this process, we need reliable assay systems that allow real-time observation and quantification of apical constriction as it occurs and permit gain- and loss-of-function analyses to explore gene function and interaction during apical constriction. In this chapter, we describe using the early Xenopus embryo as an assay system to investigate molecular mechanisms involved in apical constriction during both gastrulation and neurulation.

Shroom3, a Gene Associated with CKD, Modulates Epithelial Recovery after AKI

Background

Ischemia-induced AKI resulting in tubular damage can often progress to CKD and is a common cause of nephrology consultation. After renal tubular epithelial damage, molecular and cellular mechanisms are activated to repair and regenerate the damaged epithelium. If these mechanisms are impaired, AKI can progress to CKD. Even in patients whose kidney function returns to normal baseline are more likely to develop CKD. Genome-wide association studies have provided robust evidence that genetic variants in Shroom3, which encodes an actin-associated protein, are associated with CKD and poor outcomes in transplanted kidneys. Here, we sought to further understand the associations of Shroom3 in CKD.

Methods

Kidney ischemia was induced in wild-type (WT) and Shroom3 heterozygous null mice (Shroom3^Gt/+ ) and the mechanisms of cellular recovery and repair were examined.

Results

A 28-minute bilateral ischemia in Shroom3^Gt/+ mice resulted in 100% mortality within 24 hours. After 22-minute ischemic injury, Shroom3^Gt/+ mice had a 16% increased mortality, worsened kidney function, and significantly worse histopathology, apoptosis, proliferation, inflammation, and fibrosis after injury. The cortical tubular damage in Shroom3^Gt/+ was associated with disrupted epithelial redifferentiation, disrupted Rho-kinase/myosin signaling, and disorganized apical F-actin. Analysis of MDCK cells showed the levels of Shroom3 are directly correlated to apical organization of actin and actomyosin regulators.

Conclusion

These findings establish that Shroom3 is required for epithelial repair and redifferentiation through the organization of actomyosin regulators, and could explain why genetic variants in Shroom3 are associated with CKD and allograft rejection.

Origami: Single-cell 3D shape dynamics oriented along the apico-basal axis of folding epithelia from fluorescence microscopy data

A common feature of morphogenesis is the formation of three-dimensional structures from the folding of two-dimensional epithelial sheets, aided by cell shape changes at the cellular-level. Changes in cell shape must be studied in the context of cell-polarised biomechanical processes within the epithelial sheet. In epithelia with highly curved surfaces, finding single-cell alignment along a biological axis can be difficult to automate in silico. We present 'Origami', a MATLAB-based image analysis pipeline to compute direction-variant cell shape features along the epithelial apico-basal axis. Our automated method accurately computed direction vectors denoting the apico-basal axis in regions with opposing curvature in synthetic epithelia and fluorescence images of zebrafish embryos. As proof of concept, we identified different cell shape signatures in the developing zebrafish inner ear, where the epithelium deforms in opposite orientations to form different structures. Origami is designed to be user-friendly and is generally applicable to fluorescence images of curved epithelia.

The origin and the mechanism of mechanical polarity during epithelial folding

Epithelial tissues are sheet-like tissue structures that line the inner and outer surfaces of animal bodies and organs. Their remarkable ability to actively produce, or passively adapt to, complex surface geometries has fascinated physicists and biologists alike for centuries. The most simple and yet versatile process of epithelial deformation is epithelial folding, through which curved shapes, tissue convolutions and internal structures are produced. The advent of quantitative live imaging, combined with experimental manipulation and computational modeling, has rapidly advanced our understanding of epithelial folding. In particular, a set of mechanical principles has emerged to illustrate how forces are generated and dissipated to instigate curvature transitions in a variety of developmental contexts. Folding a tissue requires that mechanical loads or geometric changes be non-uniform. Given that polarity is the most distinct and fundamental feature of epithelia, understanding epithelial folding mechanics hinges crucially on how forces become polarized and how polarized differential deformation arises, for which I coin the term 'mechanical polarity'. In this review, five typical modules of mechanical processes are distilled from a diverse array of epithelial folding events. Their mechanical underpinnings with regard to how forces and polarity intersect are analyzed to accentuate the importance of mechanical polarity in the understanding of epithelial folding.

A three-dimensional vertex model forDrosophilasalivary gland invagination

During epithelial morphogenesis, force generation at the cellular level not only causes cell deformation, but may also produce coordinated cell movement and rearrangement on the tissue level. In this paper, we use a novel three-dimensional vertex model to explore the roles of cellular forces during the formation of the salivary gland in theDrosophilaembryo. Representing the placode as an epithelial sheet of initially columnar cells, we focus on the spatial and temporal patterning of contractile forces due to three actomyosin pools: the apicomedial actomyosin in the pit of the placode, junctional actomyosin arcs outside the pit, and a supracellular actomyosin cable along the circumference of the placode. In anin silico'wild type' model, these pools are activated at different times according to experimental data. To identify the role of each myosin pool, we have also simulated variousin silico'mutants' in which only one or two of the myosin pools are activated. We find that the apicomedial myosin initiates a small dimple in the pit, but this is not essential for the overall invagination of the placode. The myosin arcs are the main driver of invagination and are responsible for the internalization of the apical surface. The circumferential actomyosin cable acts to constrict the opening of the developing tube, and is responsible for forming a properly shaped lumen. Cell intercalation tends to facilitate the invagination, but the geometric constraints of our model only allow a small number of intercalations, and their effect is minor. The placode invagination predicted by the model is in general agreement with experimental observations. It confirms some features of the current 'belt-and-braces' model for the process, and provides new insights on the separate roles of the various myosin pools and their spatio-temporal coordination.

Actin-based force generation and cell adhesion in tissue morphogenesis

The generation of organismal form - morphogenesis - arises from forces produced at the cellular level. In animal cells, much of this force is produced by the actin cytoskeleton. Here, we review how mechanisms of actin-based force generation are deployed during animal morphogenesis to sculpt organs and organisms. Furthermore, we consider how cytoskeletal forces are coupled through cell adhesions to propagate across tissues, and discuss cases where cytoskeletal force or adhesion is patterned across a tissue to direct shape changes. Together, our review provides a conceptual framework that reflects our current understanding of animal morphogenesis and gives perspectives on future opportunities for study.

Trio cooperates with Myh9 to regulate neural crest-derived craniofacial development

Trio is a unique member of the Rho-GEF family that has three catalytic domains and is vital for various cellular processes in both physiological and developmental settings. TRIO mutations in humans are involved in craniofacial abnormalities, in which patients present with mandibular retrusion. However, little is known about the molecular mechanisms of Trio in neural crest cell (NCC)-derived craniofacial development, and there is still a lack of direct evidence to assign a functional role to Trio in NCC-induced craniofacial abnormalities. Methods: In vivo, we used zebrafish and NCC-specific knockout mouse models to investigate the phenotype and dynamics of NCC development in Trio morphants. In vitro, iTRAQ, GST pull-down assays, and proximity ligation assay (PLA) were used to explore the role of Trio and its potential downstream mediators in NCC migration and differentiation. Results: In zebrafish and mouse models, disruption of Trio elicited a migration deficit and impaired the differentiation of NCC derivatives, leading to craniofacial growth deficiency and mandibular retrusion. Moreover, Trio positively regulated Myh9 expression and directly interacted with Myh9 to coregulate downstream cellular signaling in NCCs. We further demonstrated that disruption of Trio or Myh9 inhibited Rac1 and Cdc42 activity, specifically affecting the nuclear export of β-catenin and NCC polarization. Remarkably, craniofacial abnormalities caused by trio deficiency in zebrafish could be partially rescued by the injection of mRNA encoding myh9, ca-Rac1, or ca-Cdc42. Conclusions: Here, we identified that Trio, interacting mostly with Myh9, acts as a key regulator of NCC migration and differentiation during craniofacial development. Our results indicate that trio morphant zebrafish and Wnt1-cre;Trio^fl/fl mice offer potential model systems to facilitate the study of the pathogenic mechanisms of Trio mutations causing craniofacial abnormalities.

Programmed and self-organized flow of information during morphogenesis

How the shape of embryos and organs emerges during development is a fundamental question that has fascinated scientists for centuries. Tissue dynamics arise from a small set of cell behaviours, including shape changes, cell contact remodelling, cell migration, cell division and cell extrusion. These behaviours require control over cell mechanics, namely active stresses associated with protrusive, contractile and adhesive forces, and hydrostatic pressure, as well as material properties of cells that dictate how cells respond to active stresses. In this Review, we address how cell mechanics and the associated cell behaviours are robustly organized in space and time during tissue morphogenesis. We first outline how not only gene expression and the resulting biochemical cues, but also mechanics and geometry act as sources of morphogenetic information to ultimately define the time and length scales of the cell behaviours driving morphogenesis. Next, we present two idealized modes of how this information flows - how it is read out and translated into a biological effect - during morphogenesis. The first, akin to a programme, follows deterministic rules and is hierarchical. The second follows the principles of self-organization, which rests on statistical rules characterizing the system's composition and configuration, local interactions and feedback. We discuss the contribution of these two modes to the mechanisms of four very general classes of tissue deformation, namely tissue folding and invagination, tissue flow and extension, tissue hollowing and, finally, tissue branching. Overall, we suggest a conceptual framework for understanding morphogenetic information that encapsulates genetics and biochemistry as well as mechanics and geometry as information modules, and the interplay of deterministic and self-organized mechanisms of their deployment, thereby diverging considerably from the traditional notion that shape is fully encoded and determined by genes.

A microtubule-LUZP1 association around tight junction promotes epithelial cell apical constriction

Apical constriction is critical for epithelial morphogenesis, including neural tube formation. Vertebrate apical constriction is induced by di-phosphorylated myosin light chain (ppMLC)-driven contraction of actomyosin-based circumferential rings (CRs), also known as perijunctional actomyosin rings, around apical junctional complexes (AJCs), mainly consisting of tight junctions (TJs) and adherens junctions (AJs). Here, we revealed a ppMLC-triggered system at TJ-associated CRs for vertebrate apical constriction involving microtubules, LUZP1, and myosin phosphatase. We first identified LUZP1 via unbiased screening of microtubule-associated proteins in the AJC-enriched fraction. In cultured epithelial cells, LUZP1 was found localized at TJ-, but not at AJ-, associated CRs, and LUZP1 knockout resulted in apical constriction defects with a significant reduction in ppMLC levels within CRs. A series of assays revealed that ppMLC promotes the recruitment of LUZP1 to TJ-associated CRs, where LUZP1 spatiotemporally inhibits myosin phosphatase in a microtubule-facilitated manner. Our results uncovered a hitherto unknown microtubule-LUZP1 association at TJ-associated CRs that inhibits myosin phosphatase, contributing significantly to the understanding of vertebrate apical constriction.

SHROOM3 is downstream of the planar cell polarity pathway and loss-of-function results in congenital heart defects

Congenital heart disease (CHD) is the most common birth defect, and the leading cause of death due to birth defects, yet causative molecular mechanisms remain mostly unknown. We previously implicated a novel CHD candidate gene, SHROOM3, in a patient with CHD. Using a Shroom3 gene trap knockout mouse (Shroom3^gt/gt) we demonstrate that SHROOM3 is downstream of the noncanonical Wnt planar cell polarity signaling pathway (PCP) and loss-of-function causes cardiac defects. We demonstrate Shroom3 expression within cardiomyocytes of the ventricles and interventricular septum from E10.5 onward, as well as within cardiac neural crest cells and second heart field cells that populate the cardiac outflow tract. We demonstrate that Shroom3^gt/gt mice exhibit variable penetrance of a spectrum of CHDs that include ventricular septal defects, double outlet right ventricle, and thin left ventricular myocardium. This CHD spectrum phenocopies what is observed with disrupted PCP. We show that during cardiac development SHROOM3 interacts physically and genetically with, and is downstream of, key PCP signaling component Dishevelled 2. Within Shroom3^gt/gt hearts we demonstrate disrupted terminal PCP components, actomyosin cytoskeleton, cardiomyocyte polarity, organization, proliferation and morphology. Together, these data demonstrate SHROOM3 functions during cardiac development as an actomyosin cytoskeleton effector downstream of PCP signaling, revealing SHROOM3's novel role in cardiac development and CHD.

Mouse Models of Neural Tube Defects

During embryonic development, the central nervous system forms as the neural plate and then rolls into a tube in a complex morphogenetic process known as neurulation. Neural tube defects (NTDs) occur when neurulation fails and are among the most common structural birth defects in humans. The frequency of NTDs varies greatly anywhere from 0.5 to 10 in 1000 live births, depending on the genetic background of the population, as well as a variety of environmental factors. The prognosis varies depending on the size and placement of the lesion and ranges from death to severe or moderate disability, and some NTDs are asymptomatic. This chapter reviews how mouse models have contributed to the elucidation of the genetic, molecular, and cellular basis of neural tube closure, as well as to our understanding of the causes and prevention of this devastating birth defect.

Formation and contraction of multicellular actomyosin cables facilitate lens placode invagination

Embryonic morphogenesis relies on the intrinsic ability of cells, often through remodeling the cytoskeleton, to shape epithelial tissues during development. Epithelial invagination is an example of morphogenesis that depends on this remodeling but the cellular mechanisms driving arrangement of cytoskeletal elements needed for tissue deformation remain incompletely characterized. To elucidate these mechanisms, live fluorescent microscopy and immunohistochemistry on fixed specimens were performed on chick and mouse lens placodes. This analysis revealed the formation of peripherally localized, circumferentially orientated and aligned junctions enriched in F-actin and MyoIIB. Once formed, the aligned junctions contract in a Rho-kinase and non-muscle myosin dependent manner. Further molecular characterization of these junctions revealed a Rho-kinase dependent accumulation of Arhgef11, a RhoA-specific guanine exchange factor known to regulate the formation of actomyosin cables and junctional contraction. In contrast, the localization of the Par-complex protein Par3, was reduced in these circumferentially orientated junctions. In an effort to determine if Par3 plays a negative role in MyoIIB accumulation, Par3-deficient mouse embryos were analyzed which not only revealed an increase in bicellular junctional accumulation of MyoIIB, but also a reduction of Arhgef11. Together, these results highlight the importance of the formation of the multicellular actomyosin cables that appear essential to the initiation of epithelial invagination and implicate the potential role of Arhgef11 and Par3 in their contraction and formation.

An RNAi screen unravels the complexities of Rho GTPase networks in skin morphogenesis

During mammalian embryogenesis, extensive cellular remodeling is needed for tissue morphogenesis. As effectors of cytoskeletal dynamics, Rho GTPases and their regulators are likely involved, but their daunting complexity has hindered progress in dissecting their functions. We overcome this hurdle by employing high throughput in utero RNAi-mediated screening to identify key Rho regulators of skin morphogenesis. Our screen unveiled hitherto unrecognized roles for Rho-mediated cytoskeletal remodeling events that impact hair follicle specification, differentiation, downgrowth and planar cell polarity. Coupling our top hit with gain/loss-of-function genetics, interactome proteomics and tissue imaging, we show that RHOU, an atypical Rho, governs the cytoskeletal-junction dynamics that establish columnar shape and planar cell polarity in epidermal progenitors. Conversely, RHOU downregulation is required to remodel to a conical cellular shape that enables hair bud invagination and downgrowth. Our findings underscore the power of coupling screens with proteomics to unravel the physiological significance of complex gene families.

The Molecular Basis of Human Anophthalmia and Microphthalmia

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

Evolution of the Rho guanine nucleotide exchange factors Kalirin and Trio and their gene expression in Xenopus development

Guanine nucleotide exchange factors (GEFs) activate Rho GTPases by accelerating their GDP/GTP exchange. Trio and its paralog Kalirin (Kalrn) are unique members of the Rho-GEFs that harbor three catalytic domains: two functional GEF domains and a serine/threonine kinase domain. The N-terminal GEF domain activates Rac1 and RhoG GTPases, while the C-terminal GEF domain acts specifically on RhoA. Trio and Kalrn have an evolutionary conserved function in morphogenetic processes including neuronal development. De novo mutations in TRIO have lately been identified in patients with intellectual disability, suggesting that this protein family plays an important role in development and disease. Phylogenetic and domain analysis revealed that a Kalrn/Trio ancestor originated in Prebilateria and duplicated in Urbilateria to yield Kalrn and Trio. Only few taxa outside the vertebrates retained both of these highly conserved proteins. To obtain first insights into their redundant or distinct functions in a vertebrate model system, we show for the first time a detailed comparative analysis of trio and kalrn expression in Xenopus laevis development. The mRNAs are maternally transcribed and expression increases starting with neurula stages. Trio and kalrn are detected in mesoderm/somites and different neuronal populations in the neural plate/tube and later also in the brain. However, only trio is expressed in migrating neural crest cells, while kalrn expression is detected in the cranial nerves, suggesting distinct functions. Thus, our expression analysis provides a good basis for further functional studies.

Anillin regulates epithelial cell mechanics by structuring the medial-apical actomyosin network

Cellular forces sculpt organisms during development, while misregulation of cellular mechanics can promote disease. Here, we investigate how the actomyosin scaffold protein anillin contributes to epithelial mechanics in Xenopus laevis embryos. Increased mechanosensitive recruitment of vinculin to cell-cell junctions when anillin is overexpressed suggested that anillin promotes junctional tension. However, junctional laser ablation unexpectedly showed that junctions recoil faster when anillin is depleted and slower when anillin is overexpressed. Unifying these findings, we demonstrate that anillin regulates medial-apical actomyosin. Medial-apical laser ablation supports the conclusion that that tensile forces are stored across the apical surface of epithelial cells, and anillin promotes the tensile forces stored in this network. Finally, we show that anillin's effects on cellular mechanics impact tissue-wide mechanics. These results reveal anillin as a key regulator of epithelial mechanics and lay the groundwork for future studies on how anillin may contribute to mechanical events in development and disease.

Basal epithelial tissue folding is mediated by differential regulation of microtubules

The folding of epithelial tissues is crucial for development of three-dimensional structure and function. Understanding this process can assist in determining the etiology of developmental disease and engineering of tissues for the future of regenerative medicine. Folding of epithelial tissues towards the apical surface has long been studied, but the molecular mechanisms that mediate epithelial folding towards the basal surface are just emerging. Here, we utilize zebrafish neuroepithelium to identify mechanisms that mediate basal tissue folding to form the highly conserved embryonic midbrain-hindbrain boundary. Live imaging revealed Wnt5b as a mediator of anisotropic epithelial cell shape, both apically and basally. In addition, we uncovered a Wnt5b-mediated mechanism for specific regulation of basal anisotropic cell shape that is microtubule dependent and likely to involve JNK signaling. We propose a model in which a single morphogen can differentially regulate apical versus basal cell shape during tissue morphogenesis.

Summary: Examination of cell shape changes during zebrafish neuroepithelium tissue folding reveals that Wnt5b specifically regulates basal anisotropic cell shape via a microtubule-dependent mechanism, likely involving JNK signaling.

Trio GEF mediates RhoA activation downstream of Slit2 and coordinates telencephalic wiring

Trio, a member of the Dbl family of guanine nucleotide exchange factors, activates Rac1 downstream of netrin 1/DCC signalling in axon outgrowth and guidance. Although it has been proposed that Trio also activates RhoA, the putative upstream factors remain unknown. Here, we show that Slit2 induces Trio-dependent RhoA activation, revealing a crosstalk between Slit and Trio/RhoA signalling. Consistently, we found that RhoA activity is hindered in vivo in T rio mutant mouse embryos. We next studied the development of the ventral telencephalon and thalamocortical axons, which have been previously shown to be controlled by Slit2. Remarkably, this analysis revealed that Trio knockout (KO) mice show phenotypes that bear strong similarities to the ones that have been reported in Slit2 KO mice in both guidepost corridor cells and thalamocortical axon pathfinding in the ventral telencephalon. Taken together, our results show that Trio induces RhoA activation downstream of Slit2, and support a functional role in ensuring the proper positioning of both guidepost cells and a major axonal tract. Our study indicates a novel role for Trio in Slit2 signalling and forebrain wiring, highlighting its role in multiple guidance pathways as well as in biological functions of importance for a factor involved in human brain disorders.

The scaffolding protein ZO-1 coordinates actomyosin and epithelial apical specializations in vitro and in vivo

Polarized epithelia assemble into sheets that compartmentalize organs and generate tissue barriers by integrating apical surfaces into a single, unified structure. This tissue organization is shared across organs, species, and developmental stages. The processes that regulate development and maintenance of apical epithelial surfaces are, however, undefined. Here, using an intestinal epithelial-specific knockout (KO) mouse and cultured epithelial cells, we show that the tight junction scaffolding protein zonula occludens-1 (ZO-1) is essential for development of unified apical surfaces in vivo and in vitro We found that U5 and GuK domains of ZO-1 are necessary for proper apical surface assembly, including organization of microvilli and cortical F-actin; however, direct interactions with F-actin through the ZO-1 actin-binding region (ABR) are not required. ZO-1 lacking the PDZ1 domain, which binds claudins, rescued apical structure in ZO-1-deficient epithelia, but not in cells lacking both ZO-1 and ZO-2, suggesting that heterodimerization with ZO-2 restores PDZ1-dependent ZO-1 interactions that are vital to apical surface organization. Pharmacologic F-actin disruption, myosin II motor inhibition, or dynamin inactivation restored apical epithelial structure in vitro and in vivo, indicating that ZO-1 directs epithelial organization by regulating actomyosin contraction and membrane traffic. We conclude that multiple ZO-1-mediated interactions contribute to coordination of epithelial actomyosin function and genesis of unified apical surfaces.

Radially patterned cell behaviours during tube budding from an epithelium

The budding of tubular organs from flat epithelial sheets is a vital morphogenetic process. Cell behaviours that drive such processes are only starting to be unraveled. Using live-imaging and novel morphometric methods, we show that in addition to apical constriction, radially oriented directional intercalation of cells plays a major contribution to early stages of invagination of the salivary gland tube in the Drosophila embryo. Extending analyses in 3D, we find that near the pit of invagination, isotropic apical constriction leads to strong cell-wedging. Further from the pit cells interleave circumferentially, suggesting apically driven behaviours. Supporting this, junctional myosin is enriched in, and neighbour exchanges are biased towards the circumferential orientation. In a mutant failing pit specification, neither are biased due to an inactive pit. Thus, tube budding involves radially patterned pools of apical myosin, medial as well as junctional, and radially patterned 3D-cell behaviours, with a close mechanical interplay between invagination and intercalation.

Recent advances of animal model of focal segmental glomerulosclerosis

In the last decade, great advances have been made in understanding the genetic basis for focal segmental glomerulosclerosis (FSGS). Animal models using specific gene disruption of the slit diaphragm and cytoskeleton of the foot process mirror the etiology of the human disease. Many animal models have been developed to understand the complex pathophysiology of FSGS. Therefore, we need to know the usefulness and exact methodology of creating animal models. Here, we review classic animal models and newly developed genetic animal models. Classic animal models of FSGS involve direct podocyte injury and indirect podocyte injury due to adaptive responses. However, the phenotype depends on the animal background. Renal ablation and direct podocyte toxin (PAN, adriamycin) models are leading animal models for FSGS, which have some limitations depending on mice background. A second group of animal models were developed using combinations of genetic mutation and toxin, such as NEP25, diphtheria toxin, and Thy1.1 models, which specifically injure podocytes. A third group of animal models involves genetic engineering techniques targeting podocyte expression molecules, such as podocin, CD2-associated protein, and TRPC6 channels. More detailed information about podocytopathy and FSGS can be expected in the coming decade. Different animal models should be used to study FSGS depending on the specific aim and sometimes should be used in combination.

How mechanical forces shape the developing eye

In the vertebrate embryo, the eyes develop from optic vesicles that grow laterally outward from the brain tube and contact the overlying surface ectoderm. Within the region of contact, each optic vesicle and the surface ectoderm thicken to form placodes, which then invaginate to create the optic cup and lens pit, respectively. Eventually, the optic cup becomes the retina, while the lens pit closes to form the lens vesicle. Here, we review current hypotheses for the physical mechanisms that create these structures and present novel three-dimensional computer (finite-element) models to illustrate the plausibility and limitations of these hypotheses. Taken together, experimental and numerical results suggest that the driving forces for early eye morphogenesis are generated mainly by differential growth, actomyosin contraction, and regional apoptosis, with morphology mediated by physical constraints provided by adjacent tissues and extracellular matrix. While these studies offer new insight into the mechanics of eye development, future work is needed to better understand how these mechanisms are regulated to precisely control the shape of the eye.

Apoptosis generates mechanical forces that close the lens vesicle in the chick embryo

During the initial stages of eye development, optic vesicles grow laterally outward from both sides of the forebrain and come into contact with the surrounding surface ectoderm (SE). Within the region of contact, these layers then thicken locally to create placodes and invaginate to form the optic cup (primitive retina) and lens vesicle (LV), respectively. This paper examines the biophysical mechanisms involved in LV formation, which consists of three phases: (1) lens placode formation; (2) invagination to create the lens pit (LP); and (3) closure to form a complete ellipsoidally shaped LV. Previous studies have suggested that extracellular matrix deposited between the SE and optic vesicle causes the lens placode to form by locally constraining expansion of the SE as it grows, while actomyosin contraction causes this structure to invaginate. Here, using computational modeling and experiments on chick embryos, we confirm that these mechanisms for Phases 1 and 2 are physically plausible. Our results also suggest, however, that they are not sufficient to close the LP during Phase 3. We postulate that apoptosis provides an additional mechanism by removing cells near the LP opening, thereby decreasing its circumference and generating tension that closes the LP. This hypothesis is supported by staining that shows a ring of cell death located around the LP opening during closure. Inhibiting apoptosis in cultured embryos using caspase inhibitors significantly reduced LP closure, and results from a finite-element model indicate that closure driven by cell death is plausible. Taken together, our results suggest an important mechanical role for apoptosis in lens development.

The adherens junction-associated LIM domain protein Smallish regulates epithelial morphogenesis

Cell–cell adhesion and cell shape are regulated at adherens junctions during embryonic morphogenesis. Beati et al. show that the Drosophila LIM domain protein Smallish interacts with Bazooka, Canoe, and Src42A at adherens junctions. Loss-of-function and gain-of-function phenotypes reveal a function for Smallish in regulation of actomyosin contractility and cell shape.

In epithelia, cells adhere to each other in a dynamic fashion, allowing the cells to change their shape and move along each other during morphogenesis. The regulation of adhesion occurs at the belt-shaped adherens junction, the zonula adherens (ZA). Formation of the ZA depends on components of the Par–atypical PKC (Par-aPKC) complex of polarity regulators. We have identified the Lin11, Isl-1, Mec-3 (LIM) protein Smallish (Smash), the orthologue of vertebrate LMO7, as a binding partner of Bazooka/Par-3 (Baz), a core component of the Par-aPKC complex. Smash also binds to Canoe/Afadin and the tyrosine kinase Src42A and localizes to the ZA in a planar polarized fashion. Animals lacking Smash show loss of planar cell polarity (PCP) in the embryonic epidermis and reduced cell bond tension, leading to severe defects during embryonic morphogenesis of epithelial tissues and organs. Overexpression of Smash causes apical constriction of epithelial cells. We propose that Smash is a key regulator of morphogenesis coordinating PCP and actomyosin contractility at the ZA.

The influence of living donor SHROOM3 and ABCB1 genetic variants on renal function after kidney transplantation

OBJECTIVE

A genome-wide association study has identified several gene polymorphisms associated with loss of renal function. The effect of these variants on renal function in kidney transplant recipients receiving immunosuppressive treatment is unknown.

MATERIALS AND METHODS

A cohort of 189 kidney transplant recipients and their living donors were recruited from West China Hospital of Sichuan University, on whom we assessed the association of five single nucleotide polymorphisms with renal function after kidney transplantation.

RESULTS

Glomerular filtration rate estimated by serum creatinine was significantly higher in recipients carrying allograft with the A allele at rs17319721 in SHROOM3 (shroom family member 3) than those in the group with the GG genotype from month 1 to month 6 after transplantation (P=0.020). Covariate adjustment analysis showed that the variant at rs17319721 in SHROOM3 was an independent risk factor for renal dysfunction after the first month after transplantation (P=0.022). The estimated glomerular filtration rate was the lowest in recipients with allograft carrying both the A allele at rs17319721 in SHROOM3 and the CC genotype at rs1045642 in ABCB1 (P<0.05).

CONCLUSION

The genetic variants in SHROOM3 and ABCB1 in donors were associated closely with renal function after kidney transplantation.

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.

Par3 in chick lens placode development

The lens originates from a simple cuboidal epithelium, which, on its basal side, contacts the optic vesicle, whilst facing the extraembryonic environment on its apical side. As this epithelium changes into the pseudostratified lens placode, its cells elongate and become narrower at their apical ends. This is due to the formation of an apical actin network, whose appearance is restricted to cells of the placodal region, as a result of region-specific signaling mechanisms that remain largely unknown. Here, we investigated the role of the polarity protein PAR3 and the phosphorylation state of its Threonine 833 (T833) aPKC-binding site in the recruitment of aPKC and in the establishment of actin network in the chick lens placode. Overexpression of wild type PAR3 recruited aPKC and punctate actin clusters to the basolateral membranes of the placodal cells. Recruitment of aPKC depended on the charge of the residue that replaced the T833 residue. In contrast, induction of the ectopic actin spots was independent on the charge of this residue.

Congenital Cataract in Gpr161vl/vl Mice Is Modified by Proximal Chromosome 15

The morphology and severity of human congenital cataract varies even among individuals with the same mutation, suggesting that genetic background modifies phenotypic penetrance. The spontaneous mouse mutant, vacuolated lens (vl), arose on the C3H/HeSnJ background. The mutation disrupts secondary lens fiber development by E16.5, leading to full penetrance of congenital cataract. The vl locus was mapped to a frameshift deletion in the orphan G protein-coupled receptor, Gpr161, which is expressed in differentiating lens fiber cells. When Gpr161^vl/vl C3H mice are crossed to MOLF/EiJ mice an unexpected rescue of cataract is observed, suggesting that MOLF modifiers affect cataract penetrance. Subsequent QTL analysis mapped three modifiers (Modvl3-5: Modifier of vl) and in this study we characterized Modvl4 (Chr15; LOD = 4.4). A Modvl4^MOLF congenic was generated and is sufficient to rescue congenital cataract and the lens fiber defect at E16.5. Additional phenotypic analysis on three subcongenic lines narrowed down the interval from 55 to 15Mb. In total only 18 protein-coding genes and 2 micro-RNAs are in this region. Fifteen of the 20 genes show detectable expression in the E16.5 eye. Subsequent expression studies in Gpr161^vl/vl and subcongenic E16.5 eyes, bioinformatics analysis of C3H/MOLF polymorphisms, and the biological relevancy of the genes in the interval identified three genes (Cdh6, Ank and Trio) that likely contribute to the rescue of the lens phenotype. These studies demonstrate that modification of the Gpr161^vl/vl cataract phenotype is likely due to genetic variants in at least one of three closely linked candidate genes on proximal Chr15.