Development最新文献

Tissue development relies on the coordinated differentiation of stem cells in dynamically changing environments. The formation of the vertebrate neural tube from stem cells in the caudal lateral epiblast is a well-characterized example. Despite an understanding of the signalling pathways involved, the gene regulatory mechanisms remain poorly defined. To address this, we developed a multiplexed in vivo CRISPR screening approach in chick embryos targeting genes expressed in the caudal epiblast and neural tube. This revealed a role for MLLT3, a component of the super elongation complex, in the specification of neural fate. Perturbation of MLLT3 disrupted neural tube morphology and reduced neural fate acquisition. Mutant forms of retinoic acid receptor A lacking the MLLT3 binding domain similarly reduced neural fate acquisition. Together, these findings validate an in vivo CRISPR screen strategy in chick embryos and identify a previously unreported role for MLLT3 in caudal neural tissue specification.

A successful mitosis-to-meiosis transition in germ cells is essential for fertility in sexually reproducing organisms. In mice and humans, it has been established that expression of STRA8 is crucial for meiotic onset in both sexes. Here, we show that BMP signalling is also essential, not for STRA8 induction but for correct meiotic progression in female mouse fetal germ cells. Largely in agreement with evidence from primordial germ cell-like cells (PGCLCs) in vitro, germ cell-specific deletion of BMP receptor 1A (BMPR1A; ALK3) caused aberrant retention of pluripotency marker OCT4 and meiotic progression was compromised; however, the timely onset of Stra8 and STRA8 expression was unaffected. Comparing the transcriptomes of Bmpr1a-cKO and Stra8-null models, we reveal interplay between the effects of BMP signalling and STRA8 function. Our results verify a role for BMP signalling in instructing germ cell meiosis in female mice in vivo, and shed light on the regulatory mechanisms underlying fetal germ cell development.

Despite being a major target of reconstructive surgery, development of the ear pinna remains poorly studied. Here, we provide a cellular characterization of late gestational and postnatal ear pinna development in two rodents and investigate the role of BMP5 in expansion and differentiation of auricular elastic cartilage. We find that ear pinna development is largely conserved between Mus musculus and the highly regenerative Acomys dimidiatus. The pattern of pre-cartilaginous cells is established early in development. These cells are specified into chondroblasts before ear unfolding and then undergo extensive proliferation before maturation. The elastic cartilage, connective tissue fibroblasts, dermal papilla and sheath cells, and adipocytes in the adult pinna are derived from cranial neural crest. Cellular analysis using the naturally occurring short ear mouse mutant shows that loss of BMP5 does not prevent specification of chondroblasts, but does impair chondroblast proliferation. Finally, chondroblast proliferation remains impaired in the adult mid-distal ear pinna of these mutants. Together, these data establish the developmental basis for differentiation of ear pinna tissues.

In mammalian ureters, the lamina propria presents as a prominent layer of connective tissue underneath the urothelium. Despite its important structural and signaling functions, little is known how the lamina propria develops. Here, we show that in the murine ureter the lamina propria arises at late fetal stages and massively increases by fibrocyte proliferation and collagen deposition after birth. WNT, SHH, BMP4 and retinoic acid signaling are all active in the common mesenchymal progenitor of smooth muscle cells and lamina propria fibrocytes. However, around birth, the lamina propria becomes a target for epithelial WNT and SHH signals and a source of BMP4 and retinoic acid. SHH and WNT signaling promote lamina propria and smooth muscle cell differentiation and proliferation at fetal and early postnatal stages, whereas BMP4 signaling is required for early smooth muscle cell differentiation but not for its later maintenance. Our findings suggest that, in the presence of SHH and WNT signaling, it is the modulation of BMP4 signaling which is the major determinant for the segregation of lamina propria and smooth muscle cells.

Karyotype instability in the germline leads to infertility. Unlike the female germline, the male germline continuously produces fertile sperm throughout life. Here we present a molecular network responsible for maintaining karyotype stability in the male mouse germline. Loss of the cyclin-dependent kinase inhibitor Cdkn1c in undifferentiated spermatogonia induced degeneration of spermatogenesis prior to entry into the differentiating spermatogonia. In vitro analysis of spermatogonial stem cells (SSCs) revealed that CDKN1C localized to spindle microtubules during metaphase, and that disupted microtubule dynamics increased its phosphorylation. Cdkn1c deficiency activated the spindle assembly checkpoint and led to centrosome amplification, premature chromosome segregation, and loss of AURKB, and ultimately TRP53-dependent apoptosis. Trp53-deficient SSCs exhibited karyotype defects, but proliferated normally despite reduced CDKN1C and AURKB expression. In contrast, Aurkb depletion upregulated TRP53 and CDKN1C, suggesting a negative feedback loop to maintain euploidy. Thus, Cdkn1c regulates the male germline karyotype.

Heterozygous variants in SOX10 cause congenital syndromes affecting pigmentation, digestion, hearing, and neural development, primarily attributable to failed differentiation or loss of non-skeletal neural crest derivatives. We report here an additional, previously undescribed requirement for Sox10 in bone mineralization. Neither crest- nor mesoderm-derived bones initiate mineralization on time in zebrafish sox10 mutants, despite normal osteoblast differentiation and matrix production. Mutants are deficient in the Trpv6+ ionocytes that take up calcium from the environment, resulting in severe calcium deficiency. As these ionocytes derive from ectoderm, not crest, we hypothesized that the primary defect resides in a separate organ that systemically regulates ionocyte numbers. RNA sequencing revealed significantly elevated stanniocalcin (Stc1a), an anti-hypercalcemic hormone, in sox10 mutants. Stc1a inhibits calcium uptake in fish by repressing trpv6 expression and Trpv6+ ionocyte proliferation. Epistasis assays confirm excess Stc1a as the proximate cause of the calcium deficit. The pronephros-derived glands that synthesize Stc1a interact with sox10+ cells, but these cells are missing in mutants. We conclude that sox10+ crest-derived cells non-autonomously limit Stc1a production to allow the inaugural wave of calcium uptake necessary to initiate bone mineralization.

Cell division is a fundamental process shared across diverse life forms, from yeast to humans and plants. Multicellular organisms reproduce through the formation of specialized types of cells, the gametes, which at maturity enter a quiescent state that can last decades. At the point of fertilization, signalling lifts the quiescent state and triggers cell cycle reactivation. Studying how the cell cycle is regulated during plant gamete development and fertilization is challenging, and decades of research have provided valuable, yet sometimes contradictory, insights. This Review summarizes the current understanding of plant cell cycle regulation, gamete development, quiescence, and fertilization-triggered reactivation.