Trending Papers in developmental biology

During development, gene expression regulates cell mechanics and shape to sculpt tissues. One example is epithelial folding, which proceeds through distinct cell shape changes that occur in different regions of the tissue. How transcription factors combinatorially coordinate cell shape across a tissue is poorly understood. Here, using Drosophila melanogaster as a model, we investigate how cell shape changes are coordinated to promote tissue bending during gastrulation. By quantifying the multicellular patterns of RhoA activation, F-actin, and myosin-2 and perturbing RhoA activation, we find that Snail and Twist regulate distinct patterns of graded F-actin accumulation and uniform F-actin depletion, which synergize to create zones of high and low F-actin levels within the Drosophila mesoderm. Graded actomyosin results from a gradient in RhoA activation and the width of this zone regulates tissue curvature. Thus, changes in tissue shape are regulated through the choreographed interplay of distinct gene expression patterns.### Competing Interest StatementThe authors have declared no competing interest.

Biological tubes must develop and maintain their proper diameter in order to transport materials efficiently. These tubes are molded and protected in part by apical extracellular matrices (aECMs) that line their lumens. Despite their importance, aECMs are difficult to image in vivo and therefore poorly understood. The C. elegans vulva has been a paradigm for understanding many aspects of organogenesis. Here we describe the vulva luminal matrix, which contains chondroitin proteoglycans, Zona Pellucida (ZP) domain proteins, and other glycoproteins and lipid transporters related to those in mammals. Confocal and transmission electron microscopy revealed, with unprecedented detail, a complex and dynamic aECM. Different matrix factors assemble on the apical surfaces of each vulva cell type, with clear distinctions seen between Ras-dependent (1˚) and Notch-dependent (2˚) cell types. Genetic perturbations suggest that chondroitin and other aECM factors together generate a structured scaffold that both expands and constricts lumen shape.### Competing Interest StatementThe authors have declared no competing interest.

KNOX and BELL transcription factors regulate distinct steps of diploid development in the green lineages. In the green alga Chlamydomonas reinhardtii, KNOX and BELL proteins are inherited by gametes of the opposite mating types, and heterodimerize in zygotes to activate diploid development. By contrast, in land plants such as Physcomitrella and Arabidopsis, KNOX and BELL proteins function in meristem maintenance and organogenesis during the later stages of diploid development. However, whether the contrasting functions of KNOX and BELL were acquired independently in algae and land plants is currently unknown. Here we show that in the basal land plant species Marchantia polymorpha, gamete-expressed KNOX and BELL are required to initiate zygotic development by promoting nuclear fusion in a manner strikingly similar to that of C. reinhardtii. Our results indicate that zygote activation is the ancestral role of KNOX/BELL transcription factors, which shifted toward meristem maintenance as land plants evolved.### Competing Interest Statement

Rationale: Defects in the morphogenesis of the aortic arch arteries (AAAs) are among the most severe congenital birth defects. Understanding genes and mechanisms regulating AAA formation and remodeling will provide important insights into the etiology and potential treatments of congenital heart disease. Objective: Cell-ECM interactions play essential roles in the AAA morphogenesis; however, their specific functions are not well-understood. Previously, we demonstrated that integrin a5b1 and fibronectin (Fn1) expressed in the Isl1 lineage and its derivatives regulate the formation of the pharyngeal arch arteries (PAAs), the vessels giving rise to the AAAs. The objective of these studies was to investigate the mechanisms by which integrin a5b1 and Fn1 regulate AAA morphogenesis. Methods and Results: Using temporal lineage tracing, we found that endothelial progenitors of the AAA endothelium arise early during the development of the second heart field (SHF) and that the 4th PAAs contain the highest percentage of the SHF-derived ECs (ECs). To understand the role of cell-extracellular matrix (ECM) interactions in AAA development, we deleted either integrin a5 or its major extracellular ligand Fn1 in the Isl1 lineage. We used whole-mount confocal imaging to define the complex spatial and temporal EC dynamics during PAA formation at the quantitative level and assessed how cell-ECM interactions modulated these dynamics. Our analyses demonstrated that integrin a5b1 and Fn1 mediate AAA morphogenesis by regulating the accrual of SHF-derived endothelium into the 4th pharyngeal arches and the remodeling of the 4th pharyngeal arch EC plexus into the PAAs. Following PAA formation, integrin a5b1 is essential for the activation of Notch in the neural crest-derived cells surrounding the 4th PAAs and for the differentiation of the neural crest cells into vascular smooth muscle cells. Conclusions: Our data demonstrate that cell-ECM interactions regulated by integrin a5b1 and Fn1 function reiteratively during AAA development to mediate the multi-step process of AAA morphogenesis.

Primary ciliary dyskinesia (PCD) is a human condition of dysfunctional motile cilia characterized by recurrent lung infection, infertility, organ laterality defects, and partially penetrant hydrocephalus. We recovered a mouse mutant from a forward genetic screen that developed all the phenotypes of PCD. Whole exome sequencing identified this primary ciliary dyskinesia only (Pcdo) allele to be a nonsense mutation (c.5236A>T) in the Spag17 coding sequence creating a premature stop codon at position 1746 (K1746*). The Pcdo variant abolished different isoforms of SPAG17 in the Pcdo mutant testis but not in the brain. Our data indicate differential requirements for SPAG17 in different motile cilia cell types. SPAG17 is required for proper development of the sperm flagellum, and is essential for either development or stability of the C1 microtubule structure within cilia, but not the brain ependymal cilia. We identified changes in ependymal cilia beating frequency but these did not apparently alter lateral ventricle cerebrospinal fluid (CSF) flow. Aqueductal (Aq) stenosis resulted in significantly slower and abnormally directed CSF flow and we suggest this is the root cause of the hydrocephalus. The Spag17Pcdo homozygous mutant mice are generally viable to adulthood, but have a significantly shortened life span with chronic morbidity. Our data indicate that the c.5236A>T Pcdo variant is a hypomorphic allele of Spag17 gene that causes phenotypes related to motile, but not primary, cilia. Spag17Pcdo is a novel and useful model for elucidating the molecular mechanisms underlying development of PCD in the mouse.### Competing Interest Statement

Vitellogenesis, including vitellogenin (Vg) production in the fat body and Vg uptake by maturing oocytes, is of great importance for the successful reproduction of adult females. The endocrinal and nutritional regulation of vitellogenesis differs distinctly in insects. Here, the complex crosstalk between juvenile hormone (JH) and the two nutrient sensors, insulin/IGF signaling (IIS) and target of rapamycin (TOR), was investigated to elucidate the molecular mechanisms regulating vitellogenesis in the American cockroach, Periplaneta americana. Our data showed that a block of JH biosynthesis or JH action arrested vitellogenesis, partially by inhibiting the expression of doublesex (Dsx), a key transcription factor gene involved in the sex determination cascade. Depletion of IIS and TOR blocked both JH biosynthesis and vitellogenesis. Importantly, the JH analog methoprene, but not bovine insulin (to restore IIS) and amino acids (to restore TOR activity), restored vitellogenesis in the neck-ligated (both nutrient- and JH-deficient) cockroaches. Combining classic physiology with modern molecular techniques, we have demonstrated that JH signaling alone is able to induce vitellogenesis and thus ovarian maturation. By contrast, IIS and TOR do not induce vitellogenesis independent of JH, the nutrient sensors promote vitellogenesis in an indirect manner via activating JH biosynthesis.

Cells are exposed to frequent mechanical and/or chemical stressors that can compromise the integrity of the plasma membrane and underlying cortical cytoskeleton. The molecular mechanisms driving the immediate repair response that is launched to restore the cell cortex and circumvent cell death are largely unknown. Using drug-inhibition studies and microarray analyses in the Drosophila model, we find that initiation of cell wound repair is dependent on translation, whereas transcription is required for subsequent steps in the process. We identified 253 genes whose expression is up-regulated (80) or down-regulated (173) in response to laser wounding. A subset of these genes were validated using RNAi knockdowns and found to exhibit aberrant actomyosin ring assembly and/or actin remodeling defects. Strikingly, we find that disruption of the canonical insulin signaling pathway leads to abnormal wound repair, and that it controls actin dynamics through the actin regulators Girdin and Chickadee (profilin). Our results provide new insight for understanding how cell wound repair proceeds in healthy individuals and those with diseases involving wound healing deficiencies.

Aniridia is a congenital condition characterized by absence of iris and is caused by a semidominant mutation in the transcription factor encoded by the PAX6 gene. Although ocular phenotypes of this disorder are well characterized, recent studies report that individuals with aniridia have a higher propensity for obesity, infertility, polycystic ovarian disease, and severe eczema compared to their Pax6-normal siblings. These symptoms collectively suggest an underlying endocrine disturbance related to haploinsufficient levels of Pax6. In mice, during development, Pax6 expression in the pituitary gland begins at E9.0 in the primordial anterior pituitary gland (Rathkes Pouch). This expression becomes restricted to the dorsal anterior pituitary by E11.5, but is expressed throughout the anterior lobe by E14.5, and remains through adulthood. It is possible that a reduction in Pax6 could result in a change in pituitary hormone levels or cell numbers, which may explain symptoms experienced by aniridics. Using the Small eye mouse model, we find that Pax6 reduction results in a decrease in GH-producing cells and an increase in TSH-producing cells in neonate mice, with the TSH increase continuing into adulthood. Adult Pax6 haploinsufficient mice also have an increase in anterior pituitary volume and weigh significantly less than their wild-type littermates. Furthermore, we show that the increase in TSH-producing cells leads to an increase in thyroxin (T4) in mutant mice, although tri-iodothyronine (T3) levels remain unchanged. These findings present a new role for Pax6 in the endocrine system, which serves to refine our current understanding of Pax6 in endocrine development and maintenance and provides new avenues for investigating endocrine-related symptomatology in aniridia.

Mammalian embryogenesis is a complex process controlled by transcription factors that dynamically regulate the balance between pluripotency and differentiation. Transcription factor AhR is known to regulate Oct4/Pou5f1 and Nanog, both essential genes in pluripotency, stemness and early embryo development. Yet, the molecular mechanisms controlling Oct4/Pou5f1 and Nanog during embryo development remain largely unidentified. Here, we show that AhR is required for proper embryo differentiation by regulating pluripotency factors and by maintaining adequate metabolic activity. AhR lacking embryos (AhR-/-) showed a more pluripotent phenotype characterized by a delayed expression of differentiation markers of the first and second cell divisions. Accordingly, central pluripotency factors OCT4/POU5F1, NANOG, and SOX2 were overexpressed in AhR-/- embryos at initial developmental stages. An altered intracellular localization of these factors was observed in absence of AhR and, importantly, OCT4 had an opposite expression pattern with respect to AhR from the 2-cell stage to blastocyst, suggesting a negative regulatory mechanism of OCT4/POU5F by AhR. Hippo signalling, rather than being repressed, was upregulated in very early AhR-/- embryos, possibly contributing to their undifferentiation at later stages. Consistently, AhR-null blastocysts overexpressed the early marker of inner cell mass (ICM) differentiation Sox17 whereas downregulated extraembryonic differentiation-driving genes Cdx2 and Gata3. Moreover, the persistent pluripotent phenotype of AhR-/- embryos was supported by an enhanced glycolytic metabolism and a reduction in mitochondrial activity. We propose that AhR is a regulator of pluripotency and differentiation in early mouse embryogenesis and that its deficiency may underline the reduced viability and increased resorptions of AhR-null mice.