Development最新文献

Organ and systemic growth must remain coordinated during development, even under nutritional stress. In Drosophila larvae, the intestinal microbiota contributes to this coordination by promoting growth and maturation under chronic undernutrition. Using gnotobiotic models, we show that association with Lactiplantibacillus plantarum (Lp) selectively enhances midgut growth relative to other organs, providing an adaptive mechanism that buffers the impact of dietary restriction. Transcriptomic profiling of larval midguts revealed a strong Ecdysone (Ecd) signaling signature upon Lp association. Functional analyses showed that local conversion of Ecd to its active form, 20-hydroxyecdysone, by the cytochrome P450 enzyme Shade, together with enterocyte Ecd receptor activity, is required for Lp-dependent intestinal and systemic growth. Pharmacological activation of Ecd signaling partially mimicked the bacterial effect, confirming its sufficiency to drive adaptive midgut expansion. Our results uncover an unexpected role of intestinal Ecd signaling in microbiota-driven developmental plasticity, revealing how commensal bacteria modulate local steroid signaling to fine-tune organismal growth and maturation.

While atrial septal defects (ASDs) and atrial fibrillation (AF) present differently, there is evidence that they share some genetic basis. Here, we have used directed differentiation of human induced pluripotent stem cells into atrial or ventricular cardiomyocytes (CMs) to delineate gene regulatory networks (GRNs) that define each identity. We uncovered accessible chromatin regions, transcription factor motifs and key regulatory nodes specific to, or shared by, both CM types, including the transcription factor TBX5, which is linked to genetic susceptibility of ASDs and AF in humans. Complete TBX5 loss resulted in a near absence of atrial CMs, with a concomitant increase in the abundance of other cell types. Reduced dosage of TBX5 in human atrial CMs caused cellular, electrophysiological and molecular phenotypes consistent with features of atrial CM dysfunction. This included dose-dependent aberrant accessibility of many chromatin regions and perturbation of gene regulatory networks of atrial CM identity. These results suggest that, in addition to stemming from ion channel or extracellular matrix dysfunction, atrial diseases such as ASDs or AF may result from disruptions of atrial CM identity.

Cell proliferation and differentiation are essential processes underlying multicellular organism development. Cell proliferation arrest usually precedes terminal differentiation, suggesting that these two processes may be coordinated. Here, we took advantage of the very stereotyped development of the Caenorhabditis elegans intestine to address whether the control of the proliferation and differentiation programs are systematically coupled. We show that delaying cell cycle arrest does not affect most aspects of intestinal differentiation but leads to a specific delay in the accumulation of late microvilli components. Reciprocally, we find that the differentiation factors ELT-2 and ELT-7 control cell cycle arrest specifically in posterior enterocytes. The occurrence of supernumerary divisions in the absence of ELT-2 and ELT-7 is associated with changes in the expression pattern of the cell cycle regulators cyclin B1 and CKI-1, and depends on the presence of the posterior Hox protein PHP-3. Our work thus demonstrates the existence of reciprocal interactions between cell proliferation and cell differentiation. It nevertheless also shows that these two processes are only partially coupled, suggesting the existence of additional mechanisms ensuring their temporal control.

The mTOR pathway controls the balance between anabolic and catabolic activities in animal cells, acting as a key coordinator of metabolic homeostasis. In fact, the activation of this conserved regulatory circuit promotes the biosynthesis of different macromolecules, including proteins, lipids and nucleic acids, and blocks simultaneously catabolic processes such as lysosome biogenesis. In this work we describe a biological system in which these two aspects of the mTOR function are uncoupled. Studying the sea urchin Paracentrotus lividus, we have found that the activation of the mTOR pathway in the fertilised egg, besides stimulating protein synthesis, contributes to the development of a dense array of acidic vesicles that behave as lysosomes. We present evidence indicating that mTOR could operate in this context enhancing the translation of the maternal transcripts that code for the multiple components of these organelles. We argue that the mTOR-mediated implementation of a typical catabolic process may in fact support the biosynthetic vocation of this pathway, providing energy and recycled blocks for construction.

Early life stresses impact reproductive outcomes in many organisms. In response to crowding and starvation, C. elegans nematodes form dauer larvae, in which development arrests until conditions improve. We discovered dramatic differences in gonad size and germ cell number among dauers that form under different conditions. We used live cell imaging of fluorescent proteins in otherwise wild-type and mutant animals combined with food-removal, recovery, and brood-size assays to investigate the causes and consequences of this germline difference. Pre-dauer feeding, but not nutrient sensing via the DAF-2/insulin-like signaling receptor or DAF-7/TGF-β, is required for plasticity in gonad size. Gonad differences in dauer have lifelong reproductive consequences; severely starved worms make small dauer gonads and have small broods. Pre-dauer starvation induces germline quiescence and near-instantaneous reduction of the Notch ligand LAG-2 on the germline stem cell niche. A rapid return to germline Notch dependence and an increase in presentation by the germline stem cell niche of LAG-2-independent of lag-2 transcriptional upregulation-are among the earliest events of dauer recovery.

The goal of engineering increasingly complex human organoid models is to more accurately model human organogenesis and disease. Recently, human antral gastric organoids (hAGOs) were engineered to contain splanchnic mesenchyme (SM) and enteric neural crest cells (NCCs), resulting in functional three germ layer gastric organoids. To determine the robustness of hAGOs and how additional germ layers impact development, we benchmarked these hAGOs with the developing human stomach. HAGOs in vitro were most similar to 7 week fetal stomach with the epithelium comprised primarily of mucous precursors. The SM and NCCs added to hAGOs formed fetal gastric-like mesenchymal or neuroglial precursors, respectively. Incorporation of SM and NCCs did not drastically alter the cellular diversity of the epithelium in vitro. Following transplantation, hAGOs with SM matured into tissue more like the 2nd trimester stomach. Bioinformatic inference of confirmed known signaling crosstalk between germ layers and identified new signaling candidates that may regulate tissue assembly. Together, three-germ layer hAGOs faithfully modeled the multilayer complexity of the fetal stomach at a single cell transcriptomic level and provided insight into human stomach development.

During dorsoventral patterning of bilaterian embryos, the conserved regulator Twisted gastrulation (Tsg) modulates BMP signalling by binding Chordin/Short gastrulation (Sog). Here we elucidate the mechanism by which Tsg interacts with Sog/Chordin to promote formation of the inhibitory Tsg-Sog/Chordin-BMP complex and regulate BMP signalling extracellularly. We identify and validate in vitro a hydrophobic interface in the Tsg C-terminal domain that binds Chordin. Mutation of this epitope in Drosophila Tsg (TsgL100A) results in an unexpectedly mild perturbation to embryonic BMP gradient formation. We show that a protosome-specific Tsg C-terminal extension also binds Sog, and the presence of this second binding site allows partial rescue of Sog interaction with TsgL100A in the presence of BMP. Consistent with this, a truncated Tsg protein lacking both Sog binding regions is unable to support BMP gradient formation in vivo. As our data show that disruption of either Sog binding site in Tsg, but not both, can be overcome by Tsg-BMP and Sog-BMP interactions, we present a new avidity-driven mechanism of BMP gradient formation that will be relevant to a broad range of developmental contexts.

Adherens junctions (AJs) stabilize cell contacts by coupling adhesion molecules to the cytoskeleton. AJ proteins have been studied extensively in epithelia, but less is known about their roles in other cell types. Here, we describe a role for AJ proteins in C. elegans glia. Previously, we showed that C. elegans glia use the adhesion molecule SAX-7/L1CAM to anchor the dendritic endings of URX and BAG sensory neurons at the nose during embryo elongation, allowing their dendrites to stretch to their full lengths. Using cell-specific rescue and depletion experiments, we show that the AJ proteins MAGI-1 and HMR-1/Cadherin also act in glia to promote URX and BAG dendrite extension. MAGI-1 is a multi-PDZ domain protein that can simultaneously interact with PDZ-binding (PB) motifs in SAX-7 and HMP-2/β-catenin thus potentially bridging SAX-7 to the cadherin-catenin complex. The SAX-7 PB motif also binds AFD-1/afadin. Double-mutant analyses indicate that many of these players act redundantly, consistent with parallel interactions among them. As MAGI-1, HMR-1 and AFD-1 are all found in epithelial AJs, we propose that an AJ-like complex in glia promotes dendrite extension.

Flowers are a key reproductive innovation of the angiosperms. Seed plant reproductive axes (including flowers) evolved as reproductively specialized shoots of the land plant diploid sporophyte, with the gamete-producing haploid gametophyte becoming reduced and enclosed within ovules and microsporangia. The transcription factor LEAFY (LFY) initiates floral development, yet it predates flowers and is found across all land plants. LFY function outside angiosperms is known from the moss Physcomitrium patens, where it controls the first cell division of the sporophyte, and from the model fern Ceratopteris richardii, a seedless vascular plant where CrLFY1 and CrLFY2 maintain vegetative meristem activity. However, how the floral role of LFY evolved remains unclear. Using overexpression, we uncover new roles for CrLFY1 and CrLFY2 in fern gametophyte reproduction, in sperm cells and in the gametophyte's multicellular notch meristem. While no sporophytic reproductive function was detected in terms of time to sporing, overexpression supports a role in frond compounding and in the first cell division of the zygote. Our findings suggest a potentially ancestral LFY function in fern haploid-stage reproduction, which might have been co-opted into the sporophyte during the origin of the flower.

Pioneer transcription factors are crucial for regulating zygotic genome activation and cell differentiation during mouse pre-implantation development. However, how pioneer factors function collectively to regulate early development remains poorly understood. Here, we determined the chromatin-binding profiles of the mouse pioneer factor NR5A2 during the totipotency-to-pluripotency transition and identified KLF and GATA family transcription factors as key co-regulators. NR5A2 regulates the expression of Klf5 and Gata6, the protein products of which in turn act as co-regulators of NR5A2 to promote development. Mechanistically, KLF5 contributes to H3K27ac deposition at genomic regions co-occupied by NR5A2. NR5A2 also regulates Xist expression, either directly or indirectly, through its role in co-binding with GATA factors and upregulating their expression. In vitro assays revealed that NR5A2 binds to nucleosomes with KLF5 and GATA6, suggesting that these pioneer factors can simultaneously bind to chromatin. Our findings provide evidence for a feed-forward regulatory mechanism by which NR5A2 activates expression of lineage-determining factors and these, together with NR5A2, subsequently co-bind nucleosomes to ensure robust gene activation during pre-implantation development.