Development最新文献

The process of folliculogenesis, during which the ovary develops, is an important step to ensure healthy reproduction. However, it has predominantly been studied in mice, and direct molecular comparisons to human folliculogenesis have remained technically challenging. In a new study, Hiroshi Ohta, Mitinori Saituou and colleagues perform transcriptional analysis to compare human, mouse and monkey ovarian follicles. To find out more, we spoke to first author Baku Nakakita and co-corresponding authors Mitinori Saitou, Professor at the University of Kyoto, Japan, and Hiroshi Ohta, Associate Professor at the University of Kyoto.

In zebrafish, epiboly is a major morphogenic event during gastrulation, characterized by the thinning and spreading of the embryonic blastoderm to internalize the underlying extra-embryonic yolk cell. This movement is driven by the yolk cell, which generates motile force through actomyosin flow that engages a circumferential contractile band, pulling the attached blastoderm vegetally. Localized macropinocytosis of the yolk cell, another actin-driven process, also contributes to epiboly progression by removing yolk membrane ahead of the advancing blastoderm. The molecular mechanisms coordinating these processes are elusive. Here, we identified Camsap2a, a non-centrosomal, microtubule-stabilizing protein, as a regulator of actin-dependent processes in the yolk cell during epiboly. Epiboly is delayed in camsap2a mutant embryos, which exhibit reduced macropinocytosis as well as impaired actin flow, contractile band formation and function. We show that Camsap2a functions in actin regulation upstream of the small GTPase Rab5ab, as constitutively active Rab5ab rescues the defects in macropinocytosis, actomyosin band formation and epiboly. Our work provides new insights into the molecular control of epiboly and further implicates membrane dynamics as an important contributor to the process.

Microtia is a common feature of several human syndromes affecting the external ear (pinna), yet the cellular and molecular mechanisms remain poorly understood. Using human embryos and mouse models of branchio-oto-renal (BOR) and 22q11.2 deletion syndromes, we show that the syndromic genes Eya1 and Tbx1 are expressed in mesoderm-derived auricular muscle. In Eya1 mutant mice, auricular muscles failed to form and pinna morphogenesis was disrupted, with comparable defects observed in mesoderm-specific Tbx1 mutants. Both mutant pinnae exhibited impaired cartilage differentiation, suggesting that auricular muscle provides signals to the neural crest-derived mesenchyme to regulate cartilage differentiation. In contrast, defects in cartilage development alone or loss of muscle contraction did not affect early pinna morphogenesis. Auricular myocytes expressed Fgfs, while the surrounding mesenchyme expressed Fgfr1, Fgfr2 and ERM proteins. Disrupted Fgf signalling was observed in mutant cartilage and muscle. In ex vivo cultures, inhibition of Fgf or Bmp signalling recapitulated cartilage defects, whereas BMP4 restored Sox9 expression. These findings identify the mesoderm as essential for pinna initiation and morphogenesis, and reveal signalling mechanisms underlying microtia in BOR and 22q11.2 deletion syndromes.

The role of FGF is the least understood of the morphogens driving mammalian gastrulation. Here, we have investigated FGF function in a 2D gastruloid model for human gastrulation. We observed a ring of FGF-dependent ERK activity that closely follows the emergence of primitive streak (PS)-like cells but expands further inward. This ERK activity pattern depends on localized activation of basolateral FGF receptor 1 (FGFR1) by endogenous FGF gradients and is required for PS-like differentiation, with loss of PS-like cells upon FGF receptor inhibition rescued by direct ERK activation. Single cell transcriptome analysis confirmed that, among the ligands, FGF2 is broadly expressed, FGF8 is transiently expressed during PS-like differentiation and FGF4/17 are specifically expressed in PS-like cells - similar to the human and monkey embryo but different from the mouse. FGF4 knockdown greatly reduced PS-like differentiation, while FGF17 knockdown primarily affected subsequent mesoderm differentiation. FGF8 expression was spatially and temporally displaced from PS markers and FGF4 expression, while knockdown expanded PS-like cells, suggesting FGF8 may limit PS-like differentiation. Thus, we have identified a previously unreported role for FGF-dependent ERK signaling in 2D gastruloids and possibly the human embryo, where FGF4 and FGF17 signal through basolateral FGFR1 to induce PS-like cells and derivatives, potentially restricted by FGF8.

The outer ear, called the pinna, predominantly consists of muscle and cartilage, but the molecular mechanisms that shape the developing pinna remain poorly understood. In a new study, Juan Fons, Abigail Tucker and colleagues find that coordinated development of muscle and cartilage supports pinna formation, and investigate the molecular mechanisms underpinning this. To find out more, we spoke to first author Juan Fons and corresponding author Abigail Tucker, Professor at Kings College London, UK.

The continuous growth of mouse incisors depends on the tightly coordinated proliferation and terminal differentiation of dental epithelial progenitors within the labial cervical loop (laCL). However, the molecular mechanisms governing the balance between these processes remain elusive. In this study, we identify the transcription factor ZBTB20 as a novel regulator of the proliferation-differentiation switch. ZBTB20 is predominantly expressed in the undifferentiated progenitors within laCL during late embryonic and postnatal stages. Conditional deletion of Zbtb20 in dental epithelium resulted in delayed enamel mineralization, reduced enamel volume, and excessive incisor growth. These defects were associated with enhanced proliferation and migration of transit-amplifying progenitor cells, as well as delayed pre-ameloblast and ameloblast differentiation. Integrated analysis of RNA sequencing and CUT&Tag revealed that ZBTB20 directly regulates the expression of key components of several signaling pathways, including ectodysplasin A (Eda), Notch, and Sonic Hedgehog (Shh). Our findings highlight the essential role of ZBTB20 in orchestrating the interplay among multiple signaling pathways and provide new insights into the transcription network governing the proliferation-differentiation switch of dental epithelial progenitors during incisor development.

The epicardium is a fundamental regulator of cardiac development and regeneration, functioning to secrete essential growth factors and to produce epicardium-derived cells (EPDCs) that contribute coronary mural cells and cardiac fibroblasts. The molecular mechanisms controlling epicardial formation have not been fully elucidated. In this study, we report that the RNA-binding protein SRSF3 is highly expressed in the embryonic proepicardium and epicardial layer. Deletion of Srsf3 from the murine proepicardium led to proliferative arrest, preventing proper epicardial formation. Induction of Srsf3 deletion after the proepicardial stage resulted in impaired epicardial proliferation and EPDC formation. Single-cell RNA-sequencing showed SRSF3-depleted epicardial cells were eliminated, however, the surviving non-recombined cells up-regulated Srsf3, became hyperproliferative and, remarkably, compensated for the early deficit. This unexpected finding attests the importance of SRSF3 in controlling epicardial proliferation, and highlights the significant confounding effect of mosaic recombination on embryonic phenotyping. Mapping the SRSF3-RNA interaction network by endogenous irCLIP identified binding to major cell cycle regulators, like Ccnd1 and Map4k4, mediating both splicing and non-splicing roles. This research defines SRSF3 as an important regulator of epicardial formation and function.

Hematopoietic stem and progenitor cells (HSPCs) have multilineage potential and sustain long-term self-renewal. Deriving patient-specific HSPCs has immense therapeutic potential to overcome the shortage of compatible donors for transplantation. In zebrafish, hemogenic endothelium (HE) is a specialized collection of dorsal aortic endothelial cells (ECs) that give rise to HSPCs. Our data reveal cysteine rich intestinal protein 2 (crip2) has a previously unrecognized function in establishing the proper EC environment for HSPC specification. To investigate the requirement of crip2, we generated loss-of-function alleles in crip2 and crip3, a gene family member with cardiovascular expression. crip2-/-;crip3-/- (cripDM) embryos exhibit decreased HSPC emergence with impaired lineage derivative production. Single cell RNA-sequencing of kdrl:mCherry+ ECs reveals upregulation of vascular development signature and failure to repress Notch signals during the vital transition of HE specification to HSPC emergence. Moreover, our data underscore that inhibition of Notch promotes HSPC generation in cripDM embryos and Crip genes operate through NF-κB to limit Notch. Identification of Crip2 as a novel regulator of Notch repression in HE will enhance our understanding of cues necessary to improve human HSPC production in vitro.

After optic nerve injury, several retinal ganglion cell (RGC) intrinsic signaling pathways have been shown to enhance RGC survival and RGC axonal growth. In contrast, few extrinsic cues have been identified that guide regenerating RGC axons toward and across the optic chiasm. Here, we use live-cell imaging in larval zebrafish to show that regrowing RGC axons initiate growth toward the midline and extend along a trajectory similar to their original projection. From a candidate genetic screen, we identify the glycosyltransferase Lh3 (also referred to as Plod3) to be required to direct regrowing RGC axons toward the midline during active regeneration. Moreover, we show that transgenic lh3 expression in sox10+ presumptive olig2+ oligodendrocytes located near the optic chiasm restores directed axonal growth in lh3 mutants. Finally, we find that mutants in collagen 18a1 (col18a1), a putative Lh3 substrate, display RGC axonal misguidance phenotypes similar to lh3 mutants, suggesting that lh3 may act through col18a1 during regeneration. Combined, these data identify lh3 as part of a glial derived molecular pathway critical for guiding in vivo regenerating RGC axons toward and across the optic chiasm.