Mechanisms of tissue fusion during development

CRISPR-edited, cell-based future-proof meat and seafood to enhance global food security and nutrition

Food security is a major concern due to the growing population and climate change. A method for increasing food production is the use of modern biotechnology, such as cell culture, marker-assisted selection, and genetic engineering. Cellular agriculture has enabled the production of cell-cultivated meat in bioreactors that mimic the properties of conventional meat. Furthermore, 3D food printing technology has improved food production by adding new nutritional and organoleptic properties. Marker-assisted selection and genetic engineering could play an important role in producing animals and crops with desirable traits. Therefore, integrating cellular agriculture with genetic engineering technology could be a potential strategy for the production of cell-based meat and seafood with high health benefits in the future. This review highlights the production of cell-cultivated meat derived from a variety of species, including livestock, birds, fish, and marine crustaceans. It also investigates the application of genetic engineering methods, such as CRISPR/Cas (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein), in the context of cellular agriculture. Moreover, it examines aspects such as food safety, regulatory considerations, and consumer acceptance of genetically engineered cell-cultivated meat and seafood.

Comparative analysis of testicular fusion in Spodoptera litura (cutworm) and Bombyx mori (silkworm): Histological and transcriptomic insights

Spodoptera litura commonly known as the cutworm, is among the most destructive lepidopteran pests affecting over 120 plants species. The powerful destructive nature of this lepidopteran is attributable to its high reproductive capacity. The testicular fusion that occurs during metamorphosis from larvae to pupa in S.litura positively influences the reproductive success of the offspring. In contrast, Bombyx mori, the silkworm, retains separate testes throughout its life and does not undergo this fusion process. Microscopic examination reveals that during testicular fusion in S.litura, the peritoneal sheath becomes thinner and more translucent, whereas in B.mori, the analogous region thickens. The outer basement membrane in S.litura exhibits fractures, discontinuity, and uneven thickness accompanied by a significant presence of cellular secretions, large cell size, increased vesicles, liquid droplets, and a proliferation of rough endoplasmic reticulum and mitochondria. In contrast, the testicular peritoneal sheath of B.mori at comparable developmental stage exhibits minimal change. Comparative transcriptomic analysis of the testicular peritoneal sheath reveals a substantial difference in gene expression between the two species. The disparity in differential expressed genes (DEGs) is linked to an enrichment of numerous transcription factors, intracellular signaling pathways involving Ca2+ and GTPase, as well as intracellular protein transport and signaling pathways. Meanwhile, structural proteins including actin, chitin-binding proteins, membrane protein fractions, cell adhesion, extracellular matrix proteins are predominantly identified. Moreover, the study highlights the enrichment of endopeptidases, serine proteases, proteolytic enzymes and matrix metalloproteins, which may play a role in the degradation of the outer membrane. Five transcription factors-Slforkhead, Slproline, Slcyclic, Slsilk, and SlD-ETS were identified, and their expression pattern were confirmed by qRT-PCR. they are candidates for participating in the regulation of testicular fusion. Our findings underscore significant morphological and trancriptomic variation in the testicular peritoneal sheath of S.litura compared to the silkworm, with substantial changes at the transcriptomic level coinciding with testicular fusion. The research provides valuable clues for understanding the complex mechanisms underlying this unique phenomenon in insects.

Effects of chilling and cryoprotectants on glycans in shrimp embryos

Glycans are carbohydrates present in every organism that bind to specific molecules such as lectins, a diverse group of proteins. Glycans are vital to cell proliferation and protein trafficking. In addition, embryogenesis is a critical phase in the development of marine organisms. This study investigated the effects of chilling and cryoprotective agents (CPAs) on glycans in the embryos of Stenopus hispidus. The glycan profiles of embryos of S. hispidus at the heartbeat stage were analyzed using lectin arrays. The results of analyses revealed that mannose was the most abundant glycan in the S. hispidus embryos; mannose is crucial to cell proliferation, providing the energy required for embryonic growth. Additionally, the results reveled that chilling altered the content of several glycans, including fucose and Gla-GlcNAc. Chilling may promote monosaccharide accumulation, facilitating osmotic regulation of cells and signal molecules to aid S. hispidus embryos in adapting to cold conditions. Changes were also observed in the lectins NPA, orysata, PALa, ASA, discoidin II, discoidin I, UDA, PA-IIL, and PHA-P after the samples were treated with different CPAs. DMSO may minimize cell damage during exposure to chilling by preserving cell structures, membrane properties, and functions. The present study is the first to investigate the profiles and functions of glycans in shrimp embryos subjected to low-temperature injuries. This study enhances the understanding of cell reproduction during embryogenesis and provides valuable information for the study of glycans in embryos.

Morphogenic, molecular, and cellular adaptations for unidirectional airflow in the chicken lung

Unidirectional airflow in the avian lung enables gas exchange during both inhalation and exhalation. The underlying developmental process and how it deviates from that of the bidirectional mammalian lung are poorly understood. Sampling key developmental stages with multiscale 3D imaging and single-cell transcriptomics, we delineate morphogenic, molecular, and cellular features that accommodate the unidirectional airflow in the chicken lung. Primary termini of hyper-elongated branches are eliminated via proximal-short and distal-long fusions, forming parabronchi. Neoform termini extend radially through parabronchial smooth muscle to form gas-exchanging alveoli. Supporting this radial alveologenesis, branch stalks halt their proximalization, defined by SOX9-SOX2 transition, and become SOX9 low parabronchi. Primary and secondary vascular plexi interface with primary and neoform termini, respectively. Single-cell and Stereo-seq spatial transcriptomics reveal a third, chicken-specific alveolar cell type expressing KRT14, hereby named luminal cells. Luminal, alveolar type 2, and alveolar type 1 cells sequentially occupy concentric zones radiating from the parabronchial lumen. Our study explores the evolutionary space of lung diversification and lays the foundation for functional analysis of species-specific genetic determinants.

Neurovascular anatomy of the developing human fetal penis and clitoris

The human penile and clitoral development begins from a morphologically indifferent genital tubercle. Under the influence of androgen, the genital tubercle forms the penis by forming a tubular urethra within the penile shaft. Without the effect of the androgen, the genital tubercle differentiates into the clitoris, and a lack of formation of the urethra within the clitoris is observed. Even though there are similarities during the development of the glans penis and glans clitoris, the complex canalization occurring along the penile shaft eventually leads to a morphological difference between the penis and clitoris. Based on the morphological differences, the main goal of this study was to define the vascular and neuronal anatomy of the developing penis and clitoris between 8 and 12 weeks of gestation using laser scanning confocal microscopy. Our results demonstrated there is a co-expression of CD31, which is an endothelial cell marker, and PGP9.5, which is a neuronal marker in the penis where the fusion is actively occurring at the ventral shaft. We also identified a unique anatomical structure for the first time, the clitoral ridge, which is a fetal structure running along the clitoral shaft in the vestibular groove. Contrary to previous anatomical findings which indicate that the neurovascular distribution in the developing penis and clitoris is similar, in this study, laser scanning confocal microscopy enabled us to demonstrate finer differences in the neurovascular anatomy between the penis and clitoris.

The influence of spheroid maturity on fusion dynamics and micro-tissue assembly in 3D tumor models

Three-dimensional (3D) cell culture has been used in many fields of biology because of its unique advantages. As a representative of the 3D systems, 3D spheroids are used as building blocks for tissue construction. Larger tumor aggregates can be assembled by manipulating or stacking the tumor spheroids. The motivation of this study is to investigate the behavior of the cells distributed at different locations of the spheroids in the fusion process and the mechanism behind it. To this aim, spheroids with varying grades of maturity or age were generated for fusion to assemble micro-tumor tissues. The dynamics of the fusion process, the motility of the cells distributed in different heterogeneous architecture sites, and their reactive oxygen species profiles were studied. We found that the larger the spheroid necrotic core, the slower the fusion rate of the spheroid. The cells that move were mainly distributed on the spheroid's surface during fusion. In addition to dense microfilament distribution and low microtubule content, the reactive oxygen content was high in the fusion site, while the non-fusion site was the opposite. Last, multi-spheroids with different maturities were fused to complex micro-tissues to mimic solid tumors and evaluate Doxorubicin's anti-tumor efficacy.

Exosomes Derived from Human Palatal Mesenchymal Cells Mediate Intercellular Communication During Palatal Fusion by Promoting Oral Epithelial Cell Migration

Purpose

Exosomes are important "messengers" in cell-cell interactions, but their potential effects on palatal fusion are still unknown. This study aimed to explore the role and mechanism of exosomes derived from palatal mesenchymal cells in epithelial-mesenchymal communication during palatogenesis.

Methods

The expression of exosome marker CD63 and CD81 in palatal cells during palatogenesis was detected by immunofluorescence staining. After being purified from the supernatant of human embryonic palatal mesenchymal (HEPM) cells, exosomes (HEPM-EXO) were characterized by nanoparticle tracking analysis (NTA), transmission electron microscopy (TEM) and Western blot. HEPM-EXO were co-cultured with human immortalized oral epithelial cells (HIOEC). The effects of HEPM-EXO on the cell proliferation, migration, apoptosis and epithelial-mesenchymal transition (EMT) of HIOEC were evaluated. The proteins encapsulated in HEPM-EXO were analyzed by proteomic analysis.

Results

The extensive expression of CD63 and CD81 in palatal epithelial and mesenchymal cells were continuously detected during E12.5~E14.5, suggesting that exosomes were involved in the process of palatal fusion. The expression of CD63 was also observed in the acellular basement membrane between the palatal epithelium and the mesenchyme in vivo, and HEPM-EXO could be internalized by HIOEC in vitro, suggesting that exosomes are potent to diffuse through the cellular tissue boundary to mediate palatal cell-cell communication. Exposure of HEPM-EXO to HIOEC substantially inhibited the proliferation and stimulated the migration of HIOEC, but had no significant effect on cell apoptosis and EMT. Proteomic analysis revealed the basic characteristics of the proteins in HEPM-EXO and that exosomal THBS1 may potentially regulate the cell behaviors of HIOEC, which needs further verification. Gene ontology (GO) analysis uncovered that the proteins highly expressed in HEPM-EXO are closely related to wound healing, implying a promising therapeutic opportunity of HEPM-EXO in tissue injury treatment with future studies.

Conclusion

HEPM-EXO mediated cell-cell communication by regulating cell proliferation and migration of oral epithelial cells during palatogenesis.

Claudin-3 in the non-neural ectoderm is essential for neural fold fusion in chicken embryos

The neural tube, the embryonic precursor to the brain and spinal cord, begins as a flat sheet of epithelial cells, divided into non-neural and neural ectoderm. Proper neural tube closure requires that the edges of the neural ectoderm, the neural folds, to elevate upwards and fuse along the dorsal midline of the embryo. We have previously shown that members of the claudin protein family are required for the early phases of chick neural tube closure. Claudins are transmembrane proteins, localized in apical tight junctions within epithelial cells where they are essential for regulation of paracellular permeability, strongly involved in apical-basal polarity, cell-cell adhesion, and bridging the tight junction to cytoplasmic proteins. Here we explored the role of Claudin-3 (Cldn3), which is specifically expressed in the non-neural ectoderm. We discovered that depletion of Cldn3 causes folic acid-insensitive primarily spinal neural tube defects due to a failure in neural fold fusion. Apical cell surface morphology of Cldn3-depleted non-neural ectodermal cells exhibited increased membrane blebbing and smaller apical surfaces. Although apical-basal polarity was retained, we observed altered Par3 and Pals1 protein localization patterns within the apical domain of the non-neural ectodermal cells in Cldn3-depleted embryos. Furthermore, F-actin signal was reduced at apical junctions. Our data presents a model of spina bifida, and the role that Cldn3 is playing in regulating essential apical cell processes in the non-neural ectoderm required for neural fold fusion.

Cell adhesion marker expression dynamics during fusion of the optic fissure

Tissue fusion is a critical process that is repeated in multiple contexts during embryonic development and shares common attributes to processes such as wound healing and metastasis. Ocular coloboma is a developmental eye disorder that presents as a physical gap in the ventral eye, and is a major cause of childhood blindness. Coloboma results from fusion failure between opposing ventral retinal epithelia, but there are major knowledge gaps in our understanding of this process at the molecular and cell behavioural levels. Here we catalogue the expression of cell adhesion proteins: N-cadherin, E-cadherin, R-cadherin, ZO-1, and the EMT transcriptional activator and cadherin regulator SNAI2, in the developing chicken embryonic eye. We find that fusion pioneer cells at the edges of the fusing optic fissure have unique and dynamic expression profiles for N-cad, E-cad and ZO-1, and that these are temporally preceded by expression of SNAI2. This highlights the unique properties of these cells and indicates that regulation of cell adhesion factors may be a critical process in optic fissure closure.

Epithelial apoptotic pattern emerges from global and local regulation by cell apical area

Geometry is a fundamental attribute of biological systems, and it underlies cell and tissue dynamics. Cell geometry controls cell-cycle progression and mitosis and thus modulates tissue development and homeostasis. In sharp contrast and despite the extensive characterization of the genetic mechanisms of caspase activation, we know little about whether and how cell geometry controls apoptosis commitment in developing tissues. Here, we combined multiscale time-lapse microscopy of developing Drosophila epithelium, quantitative characterization of cell behaviors, and genetic and mechanical perturbations to determine how apoptosis is controlled during epithelial tissue development. We found that early in cell lives and well before extrusion, apoptosis commitment is linked to two distinct geometric features: a small apical area compared with other cells within the tissue and a small relative apical area with respect to the immediate neighboring cells. We showed that these global and local geometric characteristics are sufficient to recapitulate the tissue-scale apoptotic pattern. Furthermore, we established that the coupling between these two geometric features and apoptotic cells is dependent on the Hippo/YAP and Notch pathways. Overall, by exploring the links between cell geometry and apoptosis commitment, our work provides important insights into the spatial regulation of cell death in tissues and improves our understanding of the mechanisms that control cell number and tissue size.

Using Biosensors to Study Organoids, Spheroids and Organs-on-a-Chip: A Mechanobiology Perspective

The increasing popularity of 3D cell culture models is being driven by the demand for more in vivo-like conditions with which to study the biochemistry and biomechanics of numerous biological processes in health and disease. Spheroids and organoids are 3D culture platforms that self-assemble and regenerate from stem cells, tissue progenitor cells or cell lines, and that show great potential for studying tissue development and regeneration. Organ-on-a-chip approaches can be used to achieve spatiotemporal control over the biochemical and biomechanical signals that promote tissue growth and differentiation. These 3D model systems can be engineered to serve as disease models and used for drug screens. While culture methods have been developed to support these 3D structures, challenges remain to completely recapitulate the cell-cell and cell-matrix biomechanical interactions occurring in vivo. Understanding how forces influence the functions of cells in these 3D systems will require precise tools to measure such forces, as well as a better understanding of the mechanobiology of cell-cell and cell-matrix interactions. Biosensors will prove powerful for measuring forces in both of these contexts, thereby leading to a better understanding of how mechanical forces influence biological systems at the cellular and tissue levels. Here, we discussed how biosensors and mechanobiological research can be coupled to develop accurate, physiologically relevant 3D tissue models to study tissue development, function, malfunction in disease, and avenues for disease intervention.

Identification and Expression of Integrins during Testicular Fusion in Spodoptera litura

Integrin members are cell adhesion receptors that bind to extracellular matrix (ECM) proteins to regulate cell-cell adhesion and cell-ECM adhesion. This process is essential for tissue development and organogenesis. The fusion of two testes is a physiological phenomenon that is required for sperm production and effective reproduction in many Lepidoptera. However, the molecular mechanism of testicular fusion is unclear. In Spodoptera litura, two separated testes fuse into a single testis during the larva-to-pupa transformation. We identified five α and five β integrin subunits that were closely associated with testicular fusion. Integrin α1 and α2 belong to the position-specific 1 (PS1) and PS2 groups, respectively. Integrin α3, αPS1/αPS2, and αPS3 were clustered into the PS3 group. Integrin β1 belonged to the insect β group, and β2, β3, and β5 were clustered in the βν group. Among these integrins, α1, α2, α3, αPS1/PS2, αPS3, β1, and β4 subunits were highly expressed when the testes fused. However, their expression levels were much lower before and after the fusion of the testis. The qRT-PCR and immunohistochemistry analyses indicated that integrin β1 mRNA and the protein were highly expressed in the peritoneal sheath of the testis, particularly when the testes fused. These results indicate that integrins might participate in S. litura testicular fusion.

Maternal stress as a risk factor for non-syndromic orofacial clefts: Systematic review and meta-analysis

Background

Non-syndromic orofacial clefts (NSOFC) are among the most common congenital malformations. Several studies have investigated the association between stress and NSOFC; however, they have reported different and heterogeneous results. Therefore, this systematic review was conducted to investigate the association between maternal periconceptional stress and non-syndromic orofacial clefts in infants.The research question was "Is maternal periconceptional stress an etiological factor for non-syndromic orofacial clefts in infants"?

Methods

Search strategy, inclusion/exclusion criteria, and data extraction from studies reporting periconceptional maternal exposure to stress and NSOFC were implemented without language restrictions. The risks of bias in the identified studies was assessed, and this information was used in the sensitivity analyses to explain heterogeneity. A meta-analysis of the extracted data was performed.

Results

Twelve eligible studies were included. Forest plot for meta-analysis of the association between maternal periconceptional exposure to stress and NSOFC among studies with adjustment for potential confounders showed a statistically significant association with an increased risk of NSOFC (odds ratio [OR]:1.17; P = 0.03), which was apparent for both cleft lip with and without palate (OR:2.07; P = 0.007) and cleft palate (OR:1.72; P = 0.003). There was a substantial heterogeneity between studies, which improved when analyzing only studies that were adjusted for potential confounders.

Conclusion

Based on the currently available evidence, maternal exposure to periconceptional stress could be considered a risk factor for NSOFCs. Therefore, we strongly recommend research investigating the effect of stress caused by the coronavirus disease-2019 pandemic on the incidence of clefts.

Won't You be My Neighbor: How Epithelial Cells Connect Together to Build Global Tissue Polarity

Epithelial tissues form continuous barriers to protect against external environments. Within these tissues, epithelial cells build environment-facing apical membranes, junction complexes that anchor neighbors together, and basolateral surfaces that face other cells. Critically, to form a continuous apical barrier, neighboring epithelial cells must align their apico-basolateral axes to create global polarity along the entire tissue. Here, we will review mechanisms of global tissue-level polarity establishment, with a focus on how neighboring epithelial cells of different origins align their apical surfaces. Epithelial cells with different developmental origins and/or that polarize at different times and places must align their respective apico-basolateral axes. Connecting different epithelial tissues into continuous sheets or tubes, termed epithelial fusion, has been most extensively studied in cases where neighboring cells initially dock at an apical-to-apical interface. However, epithelial cells can also meet basal-to-basal, posing several challenges for apical continuity. Pre-existing basement membrane between the tissues must be remodeled and/or removed, the cells involved in docking are specialized, and new cell-cell adhesions are formed. Each of these challenges can involve changes to apico-basolateral polarity of epithelial cells. This minireview highlights several in vivo examples of basal docking and how apico-basolateral polarity changes during epithelial fusion. Understanding the specific molecular mechanisms of basal docking is an area ripe for further exploration that will shed light on complex morphogenetic events that sculpt developing organisms and on the cellular mechanisms that can go awry during diseases involving the formation of cysts, fistulas, atresias, and metastases.

A unique form of collective epithelial migration is crucial for tissue fusion in the secondary palate and can overcome loss of epithelial apoptosis

Tissue fusion frequently requires the removal of an epithelium that intervenes distinct primordia to form one continuous structure. In the mammalian secondary palate, a midline epithelial seam (MES) forms between two palatal shelves and must be removed to allow mesenchymal confluence. Abundant apoptosis and cell extrusion support their importance in MES removal. However, genetically disrupting the intrinsic apoptotic regulators BAX and BAK within the MES results in complete loss of cell death and cell extrusion, but successful removal of the MES. Novel static- and live-imaging approaches reveal that the MES is removed through streaming migration of epithelial trails and islands to reach the oral and nasal epithelial surfaces. Epithelial trail cells that express the basal epithelial marker ΔNp63 begin to express periderm markers, suggesting that migration is concomitant with differentiation. Live imaging reveals anisotropic actomyosin contractility within epithelial trails, and genetic ablation of actomyosin contractility results in dispersion of epithelial collectives and failure of normal MES migration. These findings demonstrate redundancy between cellular mechanisms of morphogenesis, and reveal a crucial and unique form of collective epithelial migration during tissue fusion.

Summary: Multiple cellular processes mediate secondary palate fusion, including a unique form of streaming collective epithelial migration driven by pulsatile actomyosin contractility.

The Tbx6 Transcription Factor Dorsocross Mediates Dpp Signaling to Regulate Drosophila Thorax Closure

Movement and fusion of separate cell populations are critical for several developmental processes, such as neural tube closure in vertebrates or embryonic dorsal closure and pupal thorax closure in Drosophila. Fusion failure results in an opening or groove on the body surface. Drosophila pupal thorax closure is an established model to investigate the mechanism of tissue closure. Here, we report the identification of T-box transcription factor genes Dorsocross (Doc) as Decapentaplegic (Dpp) targets in the leading edge cells of the notum in the late third instar larval and early pupal stages. Reduction of Doc in the notum region results in a thorax closure defect, similar to that in dpp loss-of-function flies. Nine genes are identified as potential downstream targets of Doc in regulating thorax closure by molecular and genetic screens. Our results reveal a novel function of Doc in Drosophila development. The candidate target genes provide new clues for unravelling the mechanism of collective cell movement.

Consumer Acceptance and Production of In Vitro Meat: A Review

In vitro meat (IVM) is a recent development in the production of sustainable food. The consumer perception of IVM has a strong impact on the commercial success of IVM. Hence this review examines existing studies related to consumer concerns, acceptance and uncertainty of IVM. This will help create better marketing strategies for IVM-producing companies in the future. In addition, IVM production is described in terms of the types of cells and culture conditions employed. The applications of self-organising, scaffolding, and 3D printing techniques to produce IVM are also discussed. As the conditions for IVM production are controlled and can be manipulated, it will be feasible to produce a chemically safe and disease-free meat with improved consumer acceptance on a sustainable basis.

Multimodal imaging system combining optical coherence tomography and Brillouin microscopy for neural tube imaging

To understand the dynamics of tissue stiffness during neural tube formation and closure in a murine model, we have developed a multimodal, coaligned imaging system combining optical coherence tomography (OCT) and Brillouin microscopy. Brillouin microscopy can map the longitudinal modulus of tissue but cannot provide structural images. Thus, it is limited for imaging dynamic processes such as neural tube formation and closure. To overcome this limitation, we have combined Brillouin microscopy and OCT in one coaligned instrument. OCT provided depth-resolved structural imaging with a micrometer-scale spatial resolution to guide stiffness mapping by Brillouin modality. 2D structural and Brillouin frequency shift maps were acquired of mouse embryos at gestational day (GD) 8.5, 9.5, and 10.5 with the multimodal system. The results demonstrate the capability of the system to obtain structural and stiffness information simultaneously.

Proximate larval epidermal cell layer generates forces for Pupal thorax closure in Drosophila

During tissue closures, such as embryonic dorsal closure in Drosophila melanogaster, a proximate extra-embryonic layer, amnioserosa, generates forces that drive migration of the flanking lateral embryonic epidermis, thereby zip-shutting the embryo. Arguably, this paradigm of tissue closure is also recapitulated in mammalian wound healing wherein proximate fibroblasts transform into contractile myofibroblasts, develop cell junctions, and form a tissue layer de novo: contraction of the latter then aids in wound closure. Given this parallelism between disparate exemplars, we posit a general principle of tissue closure via proximate cell layer-generated forces. Here, we have tested this hypothesis in pupal thorax closure wherein 2 halves of the presumptive adult thorax of Drosophila, the contralateral heminotal epithelia, migrate over an underlying larval epidermal cell layer. We show that the proximate larval epidermal cell layer promotes thorax closure by its active contraction, orchestrated by its elaborate actomyosin network-driven epithelial cell dynamics, cell delamination, and death-the latter being prefigured by the activation of caspases. Larval epidermal cell dynamics generate contraction forces, which when relayed to the flanking heminota-via their mutual integrin-based adhesions-mediate thorax closure. Compromising any of these contraction force-generating mechanisms in the larval epidermal cell layer slows down heminotal migration, while loss of its relay to the flanking heminota abrogates the thorax closure altogether. Mathematical modeling further reconciles the biophysical underpinning of this emergent mechanism of thorax closure. Revealing mechanism of thorax closure apart, these findings show conservation of an essential principle of a proximate cell layer-driven tissue closure.

Force measurements of Myosin II waves at the yolk surface during Drosophila dorsal closure

The mechanical properties and the forces involved during tissue morphogenesis have been the focus of much research in the last years. Absolute values of forces during tissue closure events have not yet been measured. This is also true for a common force-producing mechanism involving Myosin II waves that results in pulsed cell surface contractions. Our patented magnetic tweezer, CAARMA, integrated into a spinning disk confocal microscope, provides a powerful explorative tool for quantitatively measuring forces during tissue morphogenesis. Here, we used this tool to quantify the in vivo force production of Myosin II waves that we observed at the dorsal surface of the yolk cell in stage 13 Drosophila melanogaster embryos. In addition to providing for the first time to our knowledge quantitative values on an active Myosin-driven force, we elucidated the dynamics of the Myosin II waves by measuring their periodicity in both absence and presence of external perturbations, and we characterized the mechanical properties of the dorsal yolk cell surface.

Maternal smoking during pregnancy and the risk of congenital urogenital malformations: A systematic review and meta-analysis

BACKGROUND

Investigations regarding the association between maternal smoking and specific urogenital teratogenesis exist. However, an integrated systematic review and meta-analysis studying the relationship by encompassing the whole urogenital system is essential.

OBJECTIVE

Even though many studies about inborn urogenital malformations have been conducted, its etiologic factors and exact pathogenesis are still unclear. Our aim is to assess the risk of congenital urogenital malformations in offspring of smoking pregnant women.

RESULTS

The meta-analysis, covering 41 case-control and 11 cohort studies, suggested that maternal smoking was associated with an increased risk of urogenital teratogenesis (odds ratio [OR] = 1.13, 95% confidence interval [CI]: 1.04-1.23, p = 0.005), cryptorchidism (OR = 1.18, 95%CI: 1.12-1.24, p = 0.0001), hypospadias (OR = 1.16, 95%CI: 1.01-1.33, p = 0.039), and kidney malformations (OR = 1.30, 95%CI: 1.14-1.48, p = 0.0001). Moreover, paternal smoking during the mother's pregnancy was also significantly associated (OR = 1.26, 95%CI: 1.03-1.55, p = 0.028). The association between smoking > 10 cigarettes/day was evident but was not significant (OR = 1.24, 95%CI:0.81-1.88, p = 0.323).

CONCLUSION

Our results showed that maternal smoking during pregnancy increased the risk of congenital urogenital malformations. In numerous epidemiological studies, maternal smoking during pregnancy has a significant role in fetal development. Therefore, quitting tobacco use may be an effective method for reducing the risk of congenital urogenital malformation in pregnant women.

Probing Multicellular Tissue Fusion of Cocultured Spheroids-A 3D-Bioassembly Model

While decades of research have enriched the knowledge of how to grow cells into mature tissues, little is yet known about the next phase: fusing of these engineered tissues into larger functional structures. The specific effect of multicellular interfaces on tissue fusion remains largely unexplored. Here, a facile 3D-bioassembly platform is introduced to primarily study fusion of cartilage-cartilage interfaces using spheroids formed from human mesenchymal stromal cells (hMSCs) and articular chondrocytes (hACs). 3D-bioassembly of two adjacent hMSCs spheroids displays coordinated migration and noteworthy matrix deposition while the interface between two hAC tissues lacks both cells and type-II collagen. Cocultures contribute to increased phenotypic stability in the fusion region while close initial contact between hMSCs and hACs (mixed) yields superior hyaline differentiation over more distant, indirect cocultures. This reduced ability of potent hMSCs to fuse with mature hAC tissue further underlines the major clinical challenge that is integration. Together, this data offer the first proof of an in vitro 3D-model to reliably study lateral fusion mechanisms between multicellular spheroids and mature cartilage tissues. Ultimately, this high-throughput 3D-bioassembly model provides a bridge between understanding cellular differentiation and tissue fusion and offers the potential to probe fundamental biological mechanisms that underpin organogenesis.

Programmed Cell Death Not as Sledgehammer but as Chisel: Apoptosis in Normal and Abnormal Craniofacial Patterning and Development

Coordination of craniofacial development involves an complex, intricate, genetically controlled and tightly regulated spatiotemporal series of reciprocal inductive and responsive interactions among the embryonic cephalic epithelia (both endodermal and ectodermal) and the cephalic mesenchyme — particularly the cranial neural crest (CNC). The coordinated regulation of these interactions is critical both ontogenetically and evolutionarily, and the clinical importance and mechanistic sensitivity to perturbation of this developmental system is reflected by the fact that one-third of all human congenital malformations affect the head and face. Here, we focus on one element of this elaborate process, apoptotic cell death, and its role in normal and abnormal craniofacial development. We highlight four themes in the temporospatial elaboration of craniofacial apoptosis during development, namely its occurrence at (1) positions of epithelial-epithelial apposition, (2) within intra-epithelial morphogenesis, (3) during epithelial compartmentalization, and (4) with CNC metameric organization. Using the genetic perturbation of Satb2, Pbx1/2, Fgf8, and Foxg1 as exemplars, we examine the role of apoptosis in the elaboration of jaw modules, the evolution and elaboration of the lambdoidal junction, the developmental integration at the mandibular arch hinge, and the control of upper jaw identity, patterning and development. Lastly, we posit that apoptosis uniquely acts during craniofacial development to control patterning cues emanating from core organizing centres.

Genome-wide Gene-by-Sex Interaction Studies Identify Novel Nonsyndromic Orofacial Clefts Risk Locus

Risk loci identified through genome-wide association studies have explained about 25% of the phenotypic variations in nonsyndromic orofacial clefts (nsOFCs) on the liability scale. Despite the notable sex differences in the incidences of the different cleft types, investigation of loci for sex-specific effects has been understudied. To explore the sex-specific effects in genetic etiology of nsOFCs, we conducted a genome-wide gene × sex (GxSex) interaction study in a sub-Saharan African orofacial cleft cohort. The sample included 1,019 nonsyndromic orofacial cleft cases (814 cleft lip with or without cleft palate and 205 cleft palate only) and 2,159 controls recruited from 3 sites (Ethiopia, Ghana, and Nigeria). An additive logistic model was used to examine the joint effects of the genotype and GxSex interaction. Furthermore, we examined loci with suggestive significance (P < 1E-5) in the additive model for the effect of the GxSex interaction only. We identified a novel risk locus on chromosome 8p22 with genome-wide significant joint and GxSex interaction effects (rs2720555, p_2df = 1.16E-08, p_GxSex = 1.49E-09, odds ratio [OR] = 0.44, 95% CI = 0.34 to 0.57). For males, the risk of cleft lip with or without cleft palate at this locus decreases with additional copies of the minor allele (p < 0.0001, OR = 0.60, 95% CI = 0.48 to 0.74), but the effect is reversed for females (p = 0.0004, OR = 1.36, 95% CI = 1.15 to 1.60). We replicated the female-specific effect of this locus in an independent cohort (p = 0.037, OR = 1.30, 95% CI = 1.02 to 1.65), but no significant effect was found for the males (p = 0.29, OR = 0.86, 95% CI = 0.65 to 1.14). This locus is in topologically associating domain with craniofacially expressed and enriched genes during embryonic development. Rare coding mutations of some of these genes were identified in nsOFC cohorts through whole exome sequencing analysis. Our study is additional proof that genome-wide GxSex interaction analysis provides an opportunity for novel findings of loci and genes that contribute to the risk of nsOFCs.

In-frame deletion of SPECC1L microtubule association domain results in gain-of-function phenotypes affecting embryonic tissue movement and fusion events

Patients with autosomal dominant SPECC1L variants show syndromic malformations, including hypertelorism, cleft palate and omphalocele. These SPECC1L variants largely cluster in the second coiled-coil domain (CCD2), which facilitates association with microtubules. To study SPECC1L function in mice, we first generated a null allele (Specc1lΔEx4) lacking the entire SPECC1L protein. Homozygous mutants for these truncations died perinatally without cleft palate or omphalocele. Given the clustering of human variants in CCD2, we hypothesized that targeted perturbation of CCD2 may be required. Indeed, homozygotes for in-frame deletions involving CCD2 (Specc1lΔCCD2) resulted in exencephaly, cleft palate and ventral body wall closure defects (omphalocele). Interestingly, exencephaly and cleft palate were never observed in the same embryo. Further examination revealed a narrower oral cavity in exencephalic embryos, which allowed palatal shelves to elevate and fuse despite their defect. In the cell, wildtype SPECC1L was evenly distributed throughout the cytoplasm and colocalized with both microtubules and filamentous actin. In contrast, mutant SPECC1L-ΔCCD2 protein showed abnormal perinuclear accumulation with diminished overlap with microtubules, indicating that SPECC1L used microtubule association for trafficking in the cell. The perinuclear accumulation in the mutant also resulted in abnormally increased actin and non-muscle myosin II bundles dislocated to the cell periphery. Disrupted actomyosin cytoskeletal organization in SPECC1L CCD2 mutants would affect cell alignment and coordinated movement during neural tube, palate and ventral body wall closure. Thus, we show that perturbation of CCD2 in the context of full SPECC1L protein affects tissue fusion dynamics, indicating that human SPECC1L CCD2 variants are gain-of-function.

Expanding the boundaries of synthetic development

Embryonic tissue boundaries are critical to not only cement newly patterned structures during development, but also to serve as organizing centers for subsequent rounds of morphogenesis. ​Although this latter role is especially difficult to study in vivo, synthetic embryology offers a new vantage point and fresh opportunities. In this review, we cover recent progress towards understanding and controlling in vitro boundaries and how they impact synthetic model systems. A key point this survey highlights is that the outcome of self-organization is strongly dependent on the boundary imposed, and new insight into the complex functions of embryonic boundaries will be necessary to create better self-organizing tissues for basic science, drug development, and regenerative medicine.

A genetic screen for temperature-sensitive morphogenesis-defective Caenorhabditis elegans mutants

Morphogenesis involves coordinated cell migrations and cell shape changes that generate tissues and organs, and organize the body plan. Cell adhesion and the cytoskeleton are important for executing morphogenesis, but their regulation remains poorly understood. As genes required for embryonic morphogenesis may have earlier roles in development, temperature-sensitive embryonic-lethal mutations are useful tools for investigating this process. From a collection of ∼200 such Caenorhabditis elegans mutants, we have identified 17 that have highly penetrant embryonic morphogenesis defects after upshifts from the permissive to the restrictive temperature, just prior to the cell shape changes that mediate elongation of the ovoid embryo into a vermiform larva. Using whole genome sequencing, we identified the causal mutations in seven affected genes. These include three genes that have roles in producing the extracellular matrix, which is known to affect the morphogenesis of epithelial tissues in multicellular organisms: the rib-1 and rib-2 genes encode glycosyltransferases, and the emb-9 gene encodes a collagen subunit. We also used live imaging to characterize epidermal cell shape dynamics in one mutant, or1219ts, and observed cell elongation defects during dorsal intercalation and ventral enclosure that may be responsible for the body elongation defects. These results indicate that our screen has identified factors that influence morphogenesis and provides a platform for advancing our understanding of this fundamental biological process.

Netrins: Evolutionarily Conserved Regulators of Epithelial Fusion and Closure in Development and Wound Healing

Epithelial remodelling plays a crucial role during development. The ability of epithelial sheets to temporarily lose their integrity as they fuse with other epithelial sheets underpins events such as the closure of the neural tube and palate. During fusion, epithelial cells undergo some degree of epithelial-mesenchymal transition (EMT), whereby cells from opposing sheets dissolve existing cell-cell junctions, degrade the basement membrane, extend motile processes to contact each other, and then re-establish cell-cell junctions as they fuse. Similar events occur when an epithelium is wounded. Cells at the edge of the wound undergo a partial EMT and migrate towards each other to close the gap. In this review, we highlight the emerging role of Netrins in these processes, and provide insights into the possible signalling pathways involved. Netrins are secreted, laminin-like proteins that are evolutionarily conserved throughout the animal kingdom. Although best known as axonal chemotropic guidance molecules, Netrins also regulate epithelial cells. For example, Netrins regulate branching morphogenesis of the lung and mammary gland, and promote EMT during Drosophila wing eversion. Netrins also control epithelial fusion during optic fissure closure and inner ear formation, and are strongly implicated in neural tube closure and secondary palate closure. Netrins are also upregulated in response to organ damage and epithelial wounding, and can protect against ischemia-reperfusion injury and speed wound healing in cornea and skin. Since Netrins also have immunomodulatory properties, and can promote angiogenesis and re-innervation, they hold great promise as potential factors in future wound healing therapies.

Molecular similarity between the mechanisms of epithelial fusion and fetal wound healing during the closure of the caudal neural tube in mouse embryos

BACKGROUND

Neural tube (NT) closure is a complex developmental process that takes place in the early stages of embryogenesis and that is a key step in neurulation. In mammals, the process by which the neural plate generates the NT requires organized cell movements and tissue folding, and it terminates with the fusion of the apposed ends of the neural folds.

RESULTS

Here we describe how almost identical cellular and molecular machinery is used to fuse the spinal neural folds as that involved in the repair of epithelial injury in the same area of the embryo. For both natural and wound activated closure of caudal neural tissue, hyaluronic acid and platelet-derived growth factor signaling appear to be crucial for the final fusion step.

CONCLUSIONS

There seems to be no general wound healing machinery for all tissues but rather, a tissue-specific epithelial fusion machinery that embryos activate when necessary after abnormal epithelial opening.

Structural Insights into Membrane Fusion Mediated by Convergent Small Fusogens

From lifeless viral particles to complex multicellular organisms, membrane fusion is inarguably the important fundamental biological phenomena. Sitting at the heart of membrane fusion are protein mediators known as fusogens. Despite the extensive functional and structural characterization of these proteins in recent years, scientists are still grappling with the fundamental mechanisms underlying membrane fusion. From an evolutionary perspective, fusogens follow divergent evolutionary principles in that they are functionally independent and do not share any sequence identity; however, they possess structural similarity, raising the possibility that membrane fusion is mediated by essential motifs ubiquitous to all. In this review, we particularly emphasize structural characteristics of small-molecular-weight fusogens in the hope of uncovering the most fundamental aspects mediating membrane–membrane interactions. By identifying and elucidating fusion-dependent functional domains, this review paves the way for future research exploring novel fusogens in health and disease.

Closing the Gap: Mechanisms of Epithelial Fusion During Optic Fissure Closure

A key embryonic process that occurs early in ocular development is optic fissure closure (OFC). This fusion process closes the ventral optic fissure and completes the circumferential continuity of the 3-dimensional eye. It is defined by the coming together and fusion of opposing neuroepithelia along the entire proximal-distal axis of the ventral optic cup, involving future neural retina, retinal pigment epithelium (RPE), optic nerve, ciliary body, and iris. Once these have occurred, cells within the fused seam differentiate into components of the functioning visual system. Correct development and progression of OFC, and the continued integrity of the fused margin along this axis, are important for the overall structure of the eye. Failure of OFC results in ocular coloboma-a significant cause of childhood visual impairment that can be associated with several complex ocular phenotypes including microphthalmia and anterior segment dysgenesis. Despite a large number of genes identified, the exact pathways that definitively mediate fusion have not yet been found, reflecting both the biological complexity and genetic heterogeneity of the process. This review will highlight how recent developmental studies have become focused specifically on the epithelial fusion aspects of OFC, applying a range of model organisms (spanning fish, avian, and mammalian species) and utilizing emerging high-resolution live-imaging technologies, transgenic fluorescent models, and unbiased transcriptomic analyses of segmentally-dissected fissure tissue. Key aspects of the fusion process are discussed, including basement membrane dynamics, unique cell behaviors, and the identities and fates of the cells that mediate fusion. These will be set in the context of what is now known, and how these point the way to new avenues of research.

Gene-Environment Interplay and MicroRNAs in Cleft Lip and Cleft Palate

Cleft lip (CL) with/without cleft palate (CP) (hereafter CL/P) is the second most common congenital birth defect, affecting 7.94 to 9.92 children per 10,000 live births worldwide, followed by Down syndrome. An increasing number of genes have been identified as affecting susceptibility and/or as causative genes for CL/P in mouse genetic and chemically-induced CL and CP studies, as well as in human genome-wide association studies and linkage analysis. While marked progress has been made in the identification of genetic and environmental risk factors for CL/P, the interplays between these factors are not yet fully understood. This review aims to summarize our current knowledge of CL and CP from genetically engineered mouse models and environmental factors that have been studied in mice. Understanding the regulatory mechanism(s) of craniofacial development may not only advance our understanding of craniofacial developmental biology, but could also provide approaches for the prevention of birth defects and for tissue engineering in craniofacial tissue regeneration.

Snx3 is important for mammalian neural tube closure via its role in canonical and non-canonical WNT signaling

Disruptions in neural tube (NT) closure result in neural tube defects (NTDs). To understand the molecular processes required for mammalian NT closure, we investigated the role of Snx3, a sorting nexin gene. Snx3^-/- mutant mouse embryos display a fully-penetrant cranial NTD. In vivo, we observed decreased canonical WNT target gene expression in the cranial neural epithelium of the Snx3^-/- embryos and a defect in convergent extension of the neural epithelium. Snx3^-/- cells show decreased WNT secretion, and live cell imaging reveals aberrant recycling of the WNT ligand-binding protein WLS and mis-trafficking to the lysosome for degradation. The importance of SNX3 in WNT signaling regulation is demonstrated by rescue of NT closure in Snx3^-/- embryos with a WNT agonist. The potential for SNX3 to function in human neurulation is revealed by a point mutation identified in an NTD-affected individual that results in functionally impaired SNX3 that does not colocalize with WLS and the degradation of WLS in the lysosome. These data indicate that Snx3 is crucial for NT closure via its role in recycling WLS in order to control levels of WNT signaling.

Dynamic transcriptome profiling toward understanding the development of the human embryonic heart during different Carnegie stages

Transcriptional regulation participates in heart development. However, the transcriptomes of human embryonic hearts during Carnegie stage (CS)10-CS16 have not been elucidated. Here, we found marked changes in the morphology and transcriptome of the human embryonic heart from CS10 to CS11. At CS12-CS14, the embryonic heart undergoes hypoxia-to-aerobic transformation. At CS14-CS16, transcriptome functions were related to energy metabolism, regulation of cholesterol, and processes related to inorganic substances. Moreover, the transcriptomes of cardiac progenitor cells derived from human embryonic stem cells (hESCs) most overlapped with those of human embryonic hearts at CS10. Cardiomyocytes derived from hESCs considerably overlapped with embryonic hearts at CS14-CS16. Overall, these results provide a new perspective into the characteristics of human embryonic heart development.

ROS Regulate Caspase-Dependent Cell Delamination without Apoptosis in the Drosophila Pupal Notum

Thorax fusion occurs in the midline of the Drosophila pupal notum and involves epithelial cell delamination requiring apoptotic signaling. By genetic screening, we found that NADPH oxidases (Nox and Duox) associated with superoxide anion (O˙^-₂) are responsible for caspase-3 activation and delamination. We observed that Nox is upregulated in cells that undergo delamination and that delamination depends on caspase activation. However, the cell morphology and the almost complete lack of propidium iodide incorporation suggested little membrane disruption and signified apoptotic modulation. These results demonstrate that most delaminating cells undergo caspase activation, but this activation is not sufficient for apoptosis. We showed that the expression of Catalase, encoding an H₂O₂ scavenger in the cytosol, increases delamination and induces apoptotic nuclear fragmentation in caspase-3-activated cells. These findings suggest that the roles of O˙^-₂ and intracellular H₂O₂ for delamination differs before and after caspase-3 activation, which involves live cell delamination.

Classification of aplasia cutis congenita: a 25-year review of cases presenting to a tertiary paediatric dermatology department

BACKGROUND

Aplasia cutis congenita (ACC) is a rare, congenital disorder characterized by localized or widespread absence of skin at birth with heterogeneous clinical presentation. The classification proposed by Frieden in 1986 is widely used.

AIM

To establish whether, 34 years on, the Frieden classification still meets the needs of dermatologists.

METHODS

We conducted a retrospective chart review of all patients with a diagnosis of ACC presenting over a 25-year period to a tertiary paediatric dermatology department. We compiled demographic data, clinical characteristics (e.g. number, location and morphology of the lesions), imaging and genetic results where available, and other associated abnormalities, and grouped them according to the Frieden classification. For Type 6 ACC (Bart syndrome) we reviewed neonatal photographs of all babies born with epidermolysis bullosa (EB) over 5 years.

RESULTS

Excluding Type 6, there were 56 children with ACC. The scalp was involved in 82.1%, and Type 1 was the commonest type. Over 5 years, 13 of 108 neonates (12%) with EB were born with the appearance of Type 6 ACC. Two children did not fit Frieden's original classification and one had a previously undescribed association of ACC with cleft lip/palate-ectodermal dysplasia 1 syndrome.

CONCLUSION

We conclude that the Frieden classification remains valid with some modifications. Type 3 ACC probably represents a mosaic RASopathy syndrome, while Type 7 could cover nongenetic ACC attributable to trauma. Type 8 should be subdivided into two subgroups: teratogenic and infective. Type 9 covers at least four subgroups. The classification will continue to evolve as new genes and pathomechanisms emerge.

Embryonic development of bicuspid aortic valves

Bicuspid aortic valve (BAV) is the most common congenital cardiac malformation, frequently associated with aortopathies and valvulopathies. The congenital origin of BAV is suspected to impact the development of the disease in the adult life. During the last decade, a number of studies dealing with the embryonic development of congenital heart disease have significantly improved our knowledge on BAV etiology. They describe the developmental defects, at the molecular, cellular and morphological levels, leading to congenital cardiac malformations, including BAV, in animal models. These models consist of a spontaneous hamster and several mouse models with different genetic manipulations in genes belonging to a variety of pathways. In this review paper, we aim to gather information on the developmental defects leading to BAV formation in these animal models, in order to tentatively explain the morphogenetic origin of the spectrum of valve morphologies that characterizes human BAV. BAV may be the only defect resulting from gene manipulation in mice, but usually it appears as the less severe defect of a spectrum of malformations, most frequently affecting the cardiac outflow tract. The genes whose alterations cause BAV belong to different genetic pathways, but many of them are direct or indirectly associated with the NOTCH pathway. These molecular alterations affect three basic cellular mechanisms during heart development, i.e., endocardial-to-mesenchymal transformation, cardiac neural crest (CNC) cell behavior and valve cushion mesenchymal cell differentiation. The defective cellular functions affect three possible morphogenetic mechanisms, i.e., outflow tract endocardial cushion formation, outflow tract septation and valve cushion excavation. While endocardial cushion abnormalities usually lead to latero-lateral BAVs and septation defects to antero-posterior BAVs, alterations in cushion excavation may give rise to both BAV types. The severity of the original defect most probably determines the specific aortic valve phenotype, which includes commissural fusions and raphes. Based on current knowledge on the developmental mechanisms of the cardiac outflow tract, we propose a unified hypothesis of BAV formation, based on the inductive role of CNC cells in the three mechanisms of BAV development. Alterations of CNC cell behavior in three possible alternative key valvulogenic processes may lead to the whole spectrum of BAV.

Hyaloid vasculature and mmp2 activity play a role during optic fissure fusion in zebrafish

Vertebrate retinal development requires timely and precise fusion of the optic fissure (OF). Failure of this event leads to congenital vision impairment in the form of coloboma. Recent studies have suggested hyaloid vasculature to be involved in OF fusion. In order to examine this link, we analyzed OF fusion and hyaloid vasculogenesis in the zebrafish pax2a noi mutant line. We first determined that pax2a-/- embryos fail to accumulate F-actin in the OF prior to basement membrane (BM) degradation. Furthermore, using 3D and live imaging we observed reduced OF hyaloid vascularization in pax2a-/- embryos. When examining the connection between pax2a loss of function and hyaloid vasculature, we observed significant reduction of talin1 expression, a regulator of hyaloid vasculature. In addition, cranial VEGF expression was found to be reduced in pax2a-/- embryos. Pharmacological inhibition of VEGF signaling phenocopied the pax2a-/- vasculature, F-actin and BM degradation phenotypes. Lastly, we determined that OF associated hyaloid vasculature is a source of mmp2, mmp14a and mmp14b expression and showed that mmp2 is functionally necessary for degradation of OF BM. Taken together we propose a pax2a driven mechanism that ensures proper and timely hyaloid vasculature invasion of the OF in order to facilitate availability of the BM remodeler mmp2.

Cleft lip and cleft palate in Esrp1 knockout mice is associated with alterations in epithelial-mesenchymal crosstalk

Cleft lip is one of the most common human birth defects. However, there remain a limited number of mouse models of cleft lip that can be leveraged to characterize the genes and mechanisms that cause this disorder. Crosstalk between epithelial and mesenchymal cells underlies formation of the face and palate, but the basic molecular events mediating this crosstalk remain poorly understood. We previously demonstrated that mice lacking the epithelial-specific splicing factor Esrp1 have fully penetrant bilateral cleft lip and palate. In this study, we further investigated the mechanisms leading to cleft lip as well as cleft palate in both existing and new Esrp1 mutant mouse models. These studies included a detailed transcriptomic analysis of changes in ectoderm and mesenchyme in Esrp1-/- embryos during face formation. We identified altered expression of genes previously implicated in cleft lip and/or palate, including components of multiple signaling pathways. These findings provide the foundation for detailed investigations using Esrp1 mutant disease models to examine gene regulatory networks and pathways that are essential for normal face and palate development - the disruption of which leads to orofacial clefting in human patients.

Cellular Plasticity in Breast Cancer Progression and Therapy

With the exception of non-melanoma skin cancer, breast cancer is the most frequently diagnosed malignant disease among women, with the majority of mortality being attributable to metastatic disease. Thus, even with improved early screening and more targeted treatments which may enable better detection and control of early disease progression, metastatic disease remains a significant problem. While targeted therapies exist for breast cancer patients with particular subtypes of the disease (Her2+ and ER/PR+), even in these subtypes the therapies are often not efficacious once the patient's tumor metastasizes. Increases in stemness or epithelial-to-mesenchymal transition (EMT) in primary breast cancer cells lead to enhanced plasticity, enabling tumor progression, therapeutic resistance, and distant metastatic spread. Numerous signaling pathways, including MAPK, PI3K, STAT3, Wnt, Hedgehog, and Notch, amongst others, play a critical role in maintaining cell plasticity in breast cancer. Understanding the cellular and molecular mechanisms that regulate breast cancer cell plasticity is essential for understanding the biology of breast cancer progression and for developing novel and more effective therapeutic strategies for targeting metastatic disease. In this review we summarize relevant literature on mechanisms associated with breast cancer plasticity, tumor progression, and drug resistance.

Inactivation of Zeb1 in GRHL2-deficient mouse embryos rescues mid-gestation viability and secondary palate closure

Cleft lip and palate are common birth defects resulting from failure of the facial processes to fuse during development. The mammalian grainyhead-like (Grhl1-3) genes play key roles in a number of tissue fusion processes including neurulation, epidermal wound healing and eyelid fusion. One family member, Grhl2, is expressed in the epithelial lining of the first pharyngeal arch in mice at embryonic day (E)10.5, prompting analysis of the role of this factor in palatogenesis. Grhl2-null mice die at E11.5 with neural tube defects and a cleft face phenotype, precluding analysis of palatal fusion at a later stage of development. However, in the first pharyngeal arch of Grhl2-null embryos, dysregulation of transcription factors that drive epithelial-mesenchymal transition (EMT) occurs. The aberrant expression of these genes is associated with a shift in RNA-splicing patterns that favours the generation of mesenchymal isoforms of numerous regulators. Driving the EMT perturbation is loss of expression of the EMT-suppressing transcription factors Ovol1 and Ovol2, which are direct GRHL2 targets. The expression of the miR-200 family of microRNAs, also GRHL2 targets, is similarly reduced, resulting in a 56-fold upregulation of Zeb1 expression, a major driver of mesenchymal cellular identity. The critical role of GRHL2 in mediating cleft palate in Zeb1^−/− mice is evident, with rescue of both palatal and facial fusion seen in Grhl2^−/−;Zeb1^−/− embryos. These findings highlight the delicate balance between GRHL2/ZEB1 and epithelial/mesenchymal cellular identity that is essential for normal closure of the palate and face. Perturbation of this pathway may underlie cleft palate in some patients.

Summary: Epithelial transcription factor GRHL2 is required for face closure while mesenchymal transcription factor ZEB1 is required for palate closure. Surprisingly, animals lacking both factors close their face and secondary palate.

Extracellular Matrix Composition and Remodeling: Current Perspectives on Secondary Palate Formation, Cleft Lip/Palate, and Palatal Reconstruction

Craniofacial development comprises a complex process in humans in which failures or disturbances frequently lead to congenital anomalies. Cleft lip with/without palate (CL/P) is a common congenital anomaly that occurs due to variations in craniofacial development genes, and may occur as part of a syndrome, or more commonly in isolated forms (non-syndromic). The etiology of CL/P is multifactorial with genes, environmental factors, and their potential interactions contributing to the condition. Rehabilitation of CL/P patients requires a multidisciplinary team to perform the multiple surgical, dental, and psychological interventions required throughout the patient's life. Despite progress, lip/palatal reconstruction is still a major treatment challenge. Genetic mutations and polymorphisms in several genes, including extracellular matrix (ECM) genes, soluble factors, and enzymes responsible for ECM remodeling (e.g., metalloproteinases), have been suggested to play a role in the etiology of CL/P; hence, these may be considered likely targets for the development of new preventive and/or therapeutic strategies. In this context, investigations are being conducted on new therapeutic approaches based on tissue bioengineering, associating stem cells with biomaterials, signaling molecules, and innovative technologies. In this review, we discuss the role of genes involved in ECM composition and remodeling during secondary palate formation and pathogenesis and genetic etiology of CL/P. We also discuss potential therapeutic approaches using bioactive molecules and principles of tissue bioengineering for state-of-the-art CL/P repair and palatal reconstruction.

A Three-Dimensional Organoid Culture Model to Assess the Influence of Chemicals on Morphogenetic Fusion

Embryologic development involves cell differentiation and organization events that are unique to each tissue and organ and are susceptible to developmental toxicants. Animal models are the gold standard for identifying putative teratogens, but the limited throughput of developmental toxicological studies in animals coupled with the limited concordance between animal and human teratogenicity motivates a different approach. In vitro organoid models can mimic the three-dimensional (3D) morphogenesis of developing tissues and can thus be useful tools for studying developmental toxicology. Common themes during development like the involvement of epithelial-mesenchymal transition and tissue fusion present an opportunity to develop in vitro organoid models that capture key morphogenesis events that occur in the embryo. We previously described organoids composed of human stem and progenitor cells that recapitulated the cellular features of palate fusion, and here we further characterized the model by examining pharmacological inhibitors targeting known palatogenesis and epithelial morphogenesis pathways as well as 12 cleft palate teratogens identified from rodent models. Organoid survival was dependent on signaling through EGF, IGF, HGF, and FGF pathways, and organoid fusion was disrupted by inhibition of BMP signaling. We observed concordance between the effects of EGF, FGF, and BMP inhibitors on organoid fusion and epithelial cell migration in vitro, suggesting that organoid fusion is dependent on epithelial morphogenesis. Three of the 12 putative cleft palate teratogens studied here (theophylline, triamcinolone, and valproic acid) significantly disrupted in vitro organoid fusion, while tributyltin chloride and all-trans retinoic acid were cytotoxic to fusing organoids. The study herein demonstrates the utility of the in vitro fusion assay for identifying chemicals that disrupt human organoid morphogenesis in a scalable format amenable to toxicology screening.

Oxygen and nutrient delivery in tissue engineering: Approaches to graft vascularization

The field of tissue engineering is making great strides in developing replacement tissue grafts for clinical use, marked by the rapid development of novel biomaterials, their improved integration with cells, better-directed growth and differentiation of cells, and improved three-dimensional tissue mass culturing. One major obstacle that remains, however, is the lack of graft vascularization, which in turn renders many grafts to fail upon clinical application. With that, graft vascularization has turned into one of the holy grails of tissue engineering, and for the majority of tissues, it will be imperative to achieve adequate vascularization if tissue graft implantation is to succeed. Many different approaches have been developed to induce or augment graft vascularization, both in vitro and in vivo. In this review, we highlight the importance of vascularization in tissue engineering and outline various approaches inspired by both biology and engineering to achieve and augment graft vascularization.

Mutations of GADD45G in rabbits cause cleft lip by the disorder of proliferation, apoptosis and epithelial-mesenchymal transition (EMT)

The cleft lip with or without cleft palate (CL/P) is one of the most common congenital defects in humans. Genome-wide association studies (GWAS) have been widely used for identifying candidate genes, and different genes or chromosomal regions have shown strong evidence for the presence of causal genes in CL/P. To date, two independent GWAS have identified GADD45G as influencing risk for CL/P. However, there is no animal model evidence about GADD45G related to CL/P. Here, we reported the generation of a novel GADD45G mutated rabbit model by CRISPR/Cas9 and CRISPR-based BE4-Gam systems. The homozygous (GADD45G-/-) while not heterozygous (GADD45G+/-) pups died after birth due to severe craniofacial defects of unilateral or bilateral cleft lip (CL). Moreover, the disorder of proliferation, apoptosis and epithelial-mesenchymal transition (EMT) were also determined in the medial and lateral nasal processes (MNP and LNP) of the embryonic day 13 (E13) GADD45G-/- rabbits, which compared with the normal wild type (WT) rabbits. Thus, our study confirmed for the first time that loss of GADD45G lead to CL at the animal level and provided new insights into the crucial role of GADD45G for upper lip formation and fusion.

Characterizing cleft palate toxicants using ToxCast data, chemical structure, and the biomedical literature

Cleft palate has been linked to both genetic and environmental factors that perturb key events during palatal morphogenesis. As a developmental outcome, it presents a challenging, mechanistically complex endpoint for predictive modeling. A data set of 500 chemicals evaluated for their ability to induce cleft palate in animal prenatal developmental studies was compiled from Toxicity Reference Database and the biomedical literature, which included 63 cleft palate active and 437 inactive chemicals. To characterize the potential molecular targets for chemical-induced cleft palate, we mined the ToxCast high-throughput screening database for patterns and linkages in bioactivity profiles and chemical structural descriptors. ToxCast assay results were filtered for cytotoxicity and grouped by target gene activity to produce a "gene score." Following unsuccessful attempts to derive a global prediction model using structural and gene score descriptors, hierarchical clustering was applied to the set of 63 cleft palate positives to extract local structure-bioactivity clusters for follow-up study. Patterns of enrichment were confirmed on the complete data set, that is, including cleft palate inactives, and putative molecular initiating events identified. The clusters corresponded to ToxCast assays for cytochrome P450s, G-protein coupled receptors, retinoic acid receptors, the glucocorticoid receptor, and tyrosine kinases/phosphatases. These patterns and linkages were organized into preliminary decision trees and the resulting inferences were mapped to a putative adverse outcome pathway framework for cleft palate supported by literature evidence of current mechanistic understanding. This general data-driven approach offers a promising avenue for mining chemical-bioassay drivers of complex developmental endpoints where data are often limited.

The Taiman Transcriptional Coactivator Engages Toll Signals to Promote Apoptosis and Intertissue Invasion in Drosophila

The Drosophila Taiman (Tai) protein is homologous to the human steroid-receptor coactivators SRC1-3 and activates transcription in complex with the 20-hydroxyecdysone (20E) receptor (EcR). Tai has roles in intestinal homeostasis, germline maintenance, cell motility, and proliferation through interactions with EcR and the coactivator Yorkie (Yki). Tai also promotes invasion of tumor cells in adjacent organs, but this pro-invasive mechanism is undefined. Here, we show that Tai expression transforms sessile pupal wing cells into an invasive mass that penetrates the adjacent thorax during a period of high 20E. Candidate analysis confirms a reliance on elements of the 20E and Hippo pathways, such as Yki and the Yki-Tai target dilp8. Screening the Tai-induced wing transcriptome detects enrichment for innate immune factors, including the Spätzle (Spz) family of secreted Toll ligands that induce apoptosis during cell competition. Tai-expressing wing cells induce immune signaling and apoptosis among adjacent thoracic cells, and genetic reduction of spz, Toll, or the rpr/hid/grim pro-apoptotic factors each suppresses invasion, suggesting an intercellular Spz-Toll circuit supports killing-mediated invasion. Modeling these interactions in larval epithelia confirms that Tai kills neighboring cells via a mechanism involving Toll, Spz factors, and the Spz inhibitor Necrotic. Tai-expressing cells evade death signals by repressing the immune deficiency (IMD) pathway, which operates in parallel to Toll to control nuclear factor κB (NF-κB) activity and independently regulates JNK activity. In sum, these findings suggest that Tai promotes competitive cell killing via Spz-Toll and that this killing mechanism supports pathologic intertissue invasion in Drosophila.

Spinal neural tube closure depends on regulation of surface ectoderm identity and biomechanics by Grhl2

Lack or excess expression of the surface ectoderm-expressed transcription factor Grainyhead-like2 (Grhl2), each prevent spinal neural tube closure. Here we investigate the causative mechanisms and find reciprocal dysregulation of epithelial genes, cell junction components and actomyosin properties in Grhl2 null and over-expressing embryos. Grhl2 null surface ectoderm shows a shift from epithelial to neuroepithelial identity (with ectopic expression of N-cadherin and Sox2), actomyosin disorganisation, cell shape changes and diminished resistance to neural fold recoil upon ablation of the closure point. In contrast, excessive abundance of Grhl2 generates a super-epithelial surface ectoderm, in which up-regulation of cell-cell junction proteins is associated with an actomyosin-dependent increase in local mechanical stress. This is compatible with apposition of the neural folds but not with progression of closure, unless myosin activity is inhibited. Overall, our findings suggest that Grhl2 plays a crucial role in regulating biomechanical properties of the surface ectoderm that are essential for spinal neurulation.

Loss or over-expression of Grainyhead-like transcription factors (Grhl) prevents closure of the neural tube but the mechanism underlying this is unclear. Here, the authors show that Grhl2 regulates murine posterior-neuropore closure via changes in the identity and biomechanics of the non-neural, surface ectoderm cells.

Detailed analysis of chick optic fissure closure reveals Netrin-1 as an essential mediator of epithelial fusion

Epithelial fusion underlies many vital organogenic processes during embryogenesis. Disruptions to these cause a significant number of human birth defects, including ocular coloboma. We provide robust spatial-temporal staging and unique anatomical detail of optic fissure closure (OFC) in the embryonic chick, including evidence for roles of apoptosis and epithelial remodelling. We performed complementary transcriptomic profiling and show that Netrin-1 (NTN1) is precisely expressed in the chick fissure margin during fusion but is immediately downregulated after fusion. We further provide a combination of protein localisation and phenotypic evidence in chick, humans, mice and zebrafish that Netrin-1 has an evolutionarily conserved and essential requirement for OFC, and is likely to have an important role in palate fusion. Our data suggest that NTN1 is a strong candidate locus for human coloboma and other multi-system developmental fusion defects, and show that chick OFC is a powerful model for epithelial fusion research.

Our bodies are made of many different groups of cells, which are arranged into tissues that perform specific roles. As tissues form in the embryo they must adopt precise three-dimensional structures, depending on their position in the body. In many cases this involves two edges of tissue fusing together to prevent gaps being present in the final structure.

In individuals with a condition called ocular coloboma some of the tissues in the eyes fail to merge together correctly, leading to wide gaps that can severely affect vision. There are currently no treatments available for ocular coloboma and in over 70% of patients the cause of the defect is not known. Identifying new genes that control how tissues fuse may help researchers to find what causes this condition and multiple other tissue fusion defects, and establish whether these may be preventable in the future.

Much of what is currently known about how tissues fuse has come from studying mice and zebrafish embryos. Although the extensive genetic tools available in these ‘models’ have proved very useful, both offer only a limited time window for observing tissues as they fuse, and the regions involved are very small. Chick embryos, on the other hand, are much larger than mouse or zebrafish embryos and are easier to access from within their eggs. This led Hardy et al. to investigate whether the developing chick eye could be a more useful model for studying the precise details of how tissues merge.

Examining chick embryos revealed that tissues in the base of their eyes fuse between five and eight days after the egg had been fertilised, a comparatively long time compared to existing models. Also, many of the genes that Hardy et al. found switched on in chick eyes as the tissues merged had previously been identified as being essential for tissue fusion in humans. However, several new genes were also shown to be involved in the fusing process. For example, Netrin-1 was important for tissues to fuse in the eyes as well as in other regions of the developing embryo.

These findings demonstrate that the chick eye is an excellent new model system to study how tissues fuse in animals. Furthermore, the genes identified by Hardy et al. may help researchers to identify the genetic causes of ocular coloboma and other tissue fusion defects in humans.

Mesenchymal actomyosin contractility is required for androgen-driven urethral masculinization in mice

The morphogenesis of mammalian embryonic external genitalia (eExG) shows dynamic differences between males and females. In genotypic males, eExG are masculinized in response to androgen signaling. Disruption of this process can give rise to multiple male reproductive organ defects. Currently, mechanisms of androgen-driven sexually dimorphic organogenesis are still unclear. We show here that mesenchymal-derived actomyosin contractility, by MYH10, is essential for the masculinization of mouse eExG. MYH10 is expressed prominently in the bilateral mesenchyme of male eExG. Androgen induces MYH10 protein expression and actomyosin contractility in the bilateral mesenchyme. Inhibition of actomyosin contractility through blebbistatin treatment and mesenchymal genetic deletion induced defective urethral masculinization with reduced mesenchymal condensation. We also suggest that actomyosin contractility regulates androgen-dependent mesenchymal directional cell migration to form the condensation in the bilateral mesenchyme leading to changes in urethral plate shape to accomplish urethral masculinization. Thus, mesenchymal-derived actomyosin contractility is indispensable for androgen-driven urethral masculinization.