Development最新文献

Ascidian larval muscle cells present a classic example of autonomous development. A regulatory mechanism for these cells has been extensively investigated, and the regulatory gene circuit has been documented from maternal factors to a muscle-specific gene. In the present study, we comprehensively identified genes expressed specifically in ascidian muscle cells, and found that all of them are under control of a positive regulatory loop of Tbx6-r.b and Mrf, the core circuit identified previously. We also found that several transcription factors under control of the Tbx6-r.b/Mrf regulatory loop exhibited various temporal expression profiles, which are probably important for creating functional muscle cells. These results, together with results of previous studies, provide an exhaustive view of the regulatory system enabling autonomous development of ascidian larval muscle cells. It shows that the Tbx6-r.b/Mrf regulatory loop, but not a single gene, serves a 'master' regulatory function. This master regulatory loop not only controls spatial gene expression patterns, but also governs temporal expression patterns in ascidian muscle cells.

The nuclear pore has been thought to have a consistent function during development, although its composition can vary. In this issue, Valentyna Kostiuk and colleagues reveal a context-specific role of a nucleoporin, Nup107, in the maternal-to-zygotic transition. We caught up with first author Valentyna Kostiuk and corresponding author Mustafa Khokha, Professor and Principal Investigator at Yale School of Medicine, USA, to learn more.

Proneural genes are conserved drivers of neurogenesis across the animal kingdom. How their functions have adapted to guide human-specific neurodevelopmental features is poorly understood. Here, we mined transcriptomic data from human fetal cortices and generated from human embryonic stem cell-derived cortical organoids (COs) to show that NEUROG1 and NEUROG2 are most highly expressed in basal neural progenitor cells, with pseudotime trajectory analyses indicating that NEUROG1-derived lineages predominate early and NEUROG2 lineages later. Using ChIP-qPCR, gene silencing and overexpression studies in COs, we show that NEUROG2 is necessary and sufficient to directly transactivate known target genes (NEUROD1, EOMES, RND2). To identify new targets, we engineered NEUROG2-mCherry knock-in human embryonic stem cells for CO generation. The mCherry-high CO cell transcriptome is enriched in extracellular matrix-associated genes, and two genes associated with human-accelerated regions: PPP1R17 and FZD8. We show that NEUROG2 binds COL1A1, COL3A1 and PPP1R17 regulatory elements, and induces their ectopic expression in COs, although NEUROG2 is not required for this expression. Neurog2 similarly induces Col3a1 and Ppp1r17 in murine P19 cells. These data are consistent with a conservation of NEUROG2 function across mammalian species.

The calvarial bones of the infant skull are linked by transient fibrous joints known as sutures and fontanelles, which are essential for skull compression during birth and expansion during postnatal brain growth. Genetic conditions caused by pathogenic variants in FGFR2, such as Apert, Pfeiffer, and Crouzon syndromes, result in calvarial deformities due to premature suture fusion and a persistently open anterior fontanelle (AF). In this study, we investigated how Fgfr2 regulates AF closure by leveraging mouse genetics and single-cell transcriptomics. We find that AF cells, marked by the tendon/ligament factor SCX, are spatially organized into ecto- and endocranial domains that selectively differentiate into ligament, bone, and cartilage to form the posterior frontal suture. We show that AF cell differentiation is non-autonomously regulated by FGFR2 signaling in osteogenic front cells of the frontal bones, which regulate WNT signaling in neighboring AF cells by expressing the secreted WNT inhibitor Wif1. Upon loss of Fgfr2, Wif1 expression is downregulated, and AF cells fail to form the posterior frontal suture. This study identifies an FGF-WNT signaling circuit that that directs suture formation within the AF during postnatal development.

The different spatiotemporal distribution of progenitor and neurogenic capacities permits that brain regions engage asynchronously in neurogenesis. In the hindbrain, rhombomere progenitor cells contribute to neurons during the first neurogenic phase, whereas boundary cells participate later. To analyze what maintains boundary cells as non-neurogenic progenitors, we addressed the role of Her9, a zebrafish Hes1-related protein. her9 expression is temporarily sustained in boundary cells independently of Notch at early embryonic stages, while they are non-neurogenic progenitors. Complementary functional approaches show that Her9 inhibits the onset of Notch signaling and the neurogenic program, keeping boundary cells as progenitors. Multicolor clonal analysis combined with genetic perturbations reveal that Her9 expands boundary progenitors by promoting symmetric proliferative and preventing neurogenic cell divisions. Her9 also regulates the proliferation of boundary cells by inhibiting the cell cycle arrest gene cdkn1ca and interplaying with Cyclin D1. Moreover, her9 is enriched in hindbrain radial glial cells at late embryonic stages independently of Notch. Together these data demonstrate that Her9 maintains the stemness properties of hindbrain boundary progenitors and late radial glial cells, ensuring the different temporal distribution of neurogenic capacities within the hindbrain.

To maintain and regenerate adult tissues after injury, division and differentiation of tissue-resident stem cells must be precisely regulated. It remains elusive which regulatory strategies prevent exhaustion or overgrowth of the stem cell pool, whether there is coordination between multiple mechanisms, and how to detect them from snapshots. In Drosophila testes, somatic stem cells transition to a state that licenses them to differentiate, but remain capable of returning to the niche and resuming cell division. Here, we build stochastic mathematical models for the somatic stem cell population to investigate how licensing contributes to homeostasis. We find that licensing, in combination with differentiation occurring in pairs, is sufficient to maintain homeostasis and prevent stem cell extinction from stochastic fluctuations. Experimental data have shown that stem cells are competing for niche access, and our mathematical models demonstrate that this contributes to the reduction in the variability of stem cell numbers but does not prevent extinction. Hence, a combination of both regulation strategies, licensing with pairwise differentiation and competition for niche access, may be needed to reduce variability and prevent extinction simultaneously.

Early embryos display a remarkable ability to regulate tissue patterning in response to changes in tissue size. However, it is not clear whether this ability continues into post-gastrulation stages. Here, we performed targeted removal of dorsal progenitors in the zebrafish tailbud using multiphoton ablation. This led to a proportional reduction in the length of the spinal cord and paraxial mesoderm in the tail, revealing a capacity for the regulation of tissue morphogenesis during tail formation. Following analysis of cell proliferation, gene expression, signalling and cell movements, we found no evidence of cell fate switching from mesoderm to neural fate to compensate for neural progenitor loss. Furthermore, tail paraxial mesoderm length is not reduced upon direct removal of an equivalent number of mesoderm progenitors, ruling out the hypothesis that neuromesodermal competent cells enable proportional regulation. Instead, reduction in cell number across the spinal cord reduces both spinal cord and paraxial mesoderm length. We conclude that spinal cord elongation is a driver of paraxial mesoderm elongation in the zebrafish tail and that this can explain proportional regulation upon neural progenitor reduction.

Maria Almuedo-Castillo is a Junior Group Leader at the Andalusian Center for Development Biology (CABD). Maria's group studies how mechanical forces are translated into the gene regulatory signals that impact a cell. We spoke to Maria over Teams to learn more about her early-career research, her transition into being a group leader, and her insights into navigating the academic profession.

Studies of traditional model organisms such as the fruit fly Drosophila melanogaster have contributed immensely to our understanding of the genetic basis of developmental processes. However, the generalizability of these findings cannot be confirmed without functional genetic analyses in additional organisms. Direct genome editing using targeted nucleases has the potential to transform hitherto poorly understood organisms into viable laboratory organisms for functional genetic study. To this end, we present a method to induce targeted genome knockout and knock-in of desired sequences in an insect that serves as an informative contrast to Drosophila, the cricket Gryllus bimaculatus. The efficiency of germline transmission of induced mutations is comparable with that reported for other well-studied laboratory organisms, and knock-ins targeting introns yield viable, fertile animals in which knock-in events are directly detectable by visualization of a fluorescent marker in the expression pattern of the targeted gene. Combined with the recently assembled and annotated genome of this cricket, this knock-in/knockout method increases the viability of G. bimaculatus as a tractable system for functional genetics in a basally branching insect.