Development最新文献

During development, spatial-temporally patterned tissue-level stresses and mechanical properties create diverse tissue shapes. To understand the mechanics of small-scale embryonic tissues, precisely controlled sensors and actuators are needed. Previously, we reported a control-based approach named tissue force microscopy (TiFM1.0), which combines dynamic positioning and imaging of an inserted cantilever probe to directly measure and impose forces in early avian embryos. Here, we present an upgraded system (TiFM2.0) that uses interferometer positioning to minimise probe holder footprint, enhancing accessibility and imaging signal. This new design enables a double-probe configuration for bidirectional stretching, compression and stress propagation experiments. As proof-of-concept, we showcase a variety of examples of TiFM2.0 applications in chicken and zebrafish embryos, including the characterisation of mechanical heterogeneities important for the morphogenesis of the chicken posterior body axis. We also present simplified designs and protocols for the replication of TiFM systems with minimal custom engineering for developmental biology labs.

Fracture - the initiation and propagation of cracks - has long been associated with structural failure. However, active living tissues often harness fracture as a controlled morphogenetic tool due to their unique capacities to self-organise and self-repair. In this Review, we highlight how fractures are actively interpreted, integrated and functionalised within developmental programmes to sculpt tissues across scales and species. We connect core concepts from fracture mechanics, such as stress concentration, energy release and fatigue, to biological contexts, showing how tissues actively adapt these principles by remodelling their adhesion, cytoskeleton and extracellular matrix. From reversible epithelial tears to permanent organismal fission, we discuss examples in which fracture contributes to morphogenesis, homeostasis, reproduction and egress. Further, we argue for an interdisciplinary approach to understanding how fractures emerge and drive morphogenetic transitions.

Peripheral nerve regeneration requires precise selection of the appropriate targets of innervation, often in an environment that differs from that during the developmental wiring of the neural circuit. Severed axons of the zebrafish posterior lateral line nerve have the capacity to reinnervate mechanosensory hair cells clustered in neuromast organs. Regeneration represents a balance between fasciculated regrowth of the axonal bundle and defasciculation of individual axons into the epidermis where neuromasts reside. The cues that guide pathfinding during regeneration of the posterior lateral line nerve are unknown. Here, we show that regenerating axons selectively defasciculate through distinct gaps in the epidermal boundary layer. We found that the gene col18a1a, which encodes the secreted heparan sulfate proteoglycan collagen XVIII, is expressed by the neuromast and by a subset of Schwann cells that are located at the points of axonal defasciculation. Furthermore, we observed aberrant axonal branching at inappropriate locations during nerve regeneration in col18a1a mutants. We propose a model in which collagen XVIII patterns the basement membrane to affect the precision of axonal navigation.

All exposed epithelial surfaces, including the walls of internal tubes, are lined by a lipid and glycoprotein-rich apical extracellular matrix (aECM) that helps shape and protect the apical domain. Secreted lipocalins are lipid transporters frequently found within apical compartments. We show that loss of the Caenorhabditis elegans lipocalin LPR-1 disrupts the assembly of another lipocalin, LPR-3, within the pre-cuticle aECM that protects and shapes the narrow excretory duct and pore tubes. Loss of SCAV-2, a CD36 family scavenger receptor, restored LPR-3 matrix localization and suppressed the tube shaping defects of lpr-1 and a subset of pre-cuticle mutants, but not lpr-3 mutants. SCAV-2 accumulates at duct and pore apical surfaces and functions locally within these tubes. These data demonstrate that LPR-1 and SCAV-2 have opposing effects on narrow tube integrity by altering the content and organization of the luminal aECM of the tube, possibly by acting as transporters of LPR-3 or an LPR-3 cofactor. These results have broadly relevant implications regarding the importance of lipocalins and scavenger receptors for aECM organization and integrity of the narrowest tubes in the body.

Ovulation enables mature oocytes to exit the ovary for potential fertilization. In Drosophila, ovulation is induced by mating but also occurs spontaneously in virgins, with rates varying widely in natural populations: short oocyte retention is ancestral, while longer retention is favored in colder climates. The molecular regulation of spontaneous ovulation remains unclear. Here, we show that disrupting the relaxin/insulin-like peptide Dilp8 or its receptor Lgr3-an orthologue of vertebrate RXFP1/2-in follicle cells or specific neurons, respectively, delays ovulation, slows average egg transit time in the reproductive tract, and facilitates oogenesis progression beyond ∼2 mature oocytes per ovariole, leading to mature follicle accumulation in the ovary. Mating largely rescues these defects, suggesting the pathway is dispensable post-mating. Dilp8-Lgr3 signaling ensures high oocyte quality by promoting elimination of lower-quality aging oocytes and by antagonizing oogenesis progression via an undefined mechanism downstream of Lgr3+ neurons. Our findings provide a molecular basis for oocyte retention time regulation in Drosophila involving ovarian-nervous system cross-talk, and bring further support for an ancient, conserved role for relaxin-like signaling in regulating ovulation and overall female reproductive physiology.

Tissue-intrinsic surveillance systems maintain tissue health by detecting and eliminating aberrant cells. One such mechanism, interface surveillance, is activated by differences in cell fate programs between neighboring cells, leading to actomyosin accumulation, JNK-signaling, and apoptosis at these interfaces. Here, we identify long Toll receptors (Toll-2, Toll-6, Toll-7, Toll-8) as mediators of interface surveillance in Drosophila imaginal discs. Using genetic mosaics and mapping of expression pattern, we show that differences in long Toll receptor levels between adjacent cells are sufficient to induce all hallmarks of interface surveillance. This response relies on the comparison of relative expression levels set by fate-specifying pathways and is thus position-dependent. Specifically, long Toll receptor expression is regulated by multiple patterning pathways, generating a combinatorial cell-surface code that is disrupted in developmentally aberrant or oncogenic cells. Notably, interface surveillance functions independently of NF-κB signaling, rather reflecting a role for long Toll receptors in modulating cell affinity through actomyosin dynamics. Our findings reveal long Toll receptors as integrators of developmental patterning and tissue homeostasis and provide insights into how tissues detect and respond to aberrant or oncogenic mutations.

While DIS3 functions in male germ cells are emerging, its ribonuclease activity governing Sertoli cell RNA metabolism, essential for testicular development and spermatogenesis, remains undefined. This study identifies a critical role for exosome-associated DIS3 ribonuclease in regulating Sertoli cell maintenance and maturation during spermatogenesis. Dis3 deficiency in Sertoli cells causes severe testicular atrophy, marked by rapid depletion of both Sertoli and germ cells. This phenotype results from impaired Sertoli cell proliferation, elevated apoptosis, disrupted maturation, and compromised blood-testis barrier integrity, culminating in defective spermatogenesis and infertility. scRNA-seq analysis reveals altered cell-cell communication, alongside heightened p53 and Wnt signaling activity in Dis3 cKO Sertoli cells. p53 inhibitor treatment mitigates overt apoptosis in Dis3 cKO Sertoli cells. Similarly, inhibition of the Wnt/β-Catenin pathway increases the abundance of both Sertoli and germ cells while improving Sertoli cell maturation. Together, these findings establish Sertoli cell-specific DIS3 as essential for testicular development and spermatogenesis in mice, and implicate the p53 and Wnt/β-Catenin pathways as potential mechanistic contributors.

SLIT2 is a secreted protein that repels axons from the CNS midline. Full-length SLIT2 (SLIT2-FL) is proteolytically cleaved into two fragments, SLIT2-N and SLIT2-C. SLIT2-FL and SLIT2-N have opposing biological effects on cultured dorsal root ganglion (DRG) axons. This study identified SLIT2 cleavage mechanisms and functional significance for DRG axon guidance. The Tolloid related protease TLL1 cleaved SLIT2 in cultured cells, with TLL1 requiring activation by furin/prohormone convertases. We used CRISPR editing in mice to produce a Slit2DTLS allele lacking the TLL1 cleavage site. Slit2DTLS embryos retained dorsal repulsion of DRG axons, in contrast to DRG midline invasion in Slit2 knockouts. However, DRG axons in Slit2 knockouts and Slit2DTLS mutants showed reduced fasciculation of rootlets and longitudinal DRG projections. In vitro, SLIT2-N promoted fasciculation of DRG axons. These results suggest that proteolytic cleavage generates additional SLIT2 biological functions for organizing DRG central axon projections.

Understanding the mechanisms for human ovarian folliculogenesis is fundamental to reproductive biology and medicine. Here, we investigated transcriptomic dynamics in individual oocytes and their associated granulosa cells (GCs) during folliculogenesis in mice, monkeys and humans. Unlike mouse oocytes, which exhibited stage-specific, stepwise transcriptomic maturation, monkey and human oocytes showed minimal transcriptomic changes until the secondary follicle stage and could be broadly categorized as either immature or mature. In all three species, most highly variable genes during oocyte growth displayed monotonic up- or downregulation, with limited overlap in highly variable genes across species. GCs exhibited similarly species-specific transcriptomic trajectories. Correspondingly, intercellular communication pathways, including ligand-receptor signaling, gap junctions, and metabolic coupling between oocytes and GCs, demonstrated substantial species-specific differences. Nonetheless, X-chromosome dosage compensation and repression of evolutionarily young transposons were conserved across species. We established in vitro culture systems supporting preantral to antral follicle development in monkeys and humans, revealing relatively normal oocyte transcriptome maturation but aberrant GC profiles. By delineating interspecies differences in folliculogenesis, this study provides a framework for understanding human ovarian development and advancing its in vitro reconstruction.

The kidney collecting system develops from the ureteric bud (UB), which undergoes multiple rounds of iterative branching. This process is controlled by growth factors and requires the interaction between the extracellular matrix and β1-containing integrin receptors. Integrin affinity for its ligands is regulated by integrin-binding proteins including kindlins, which bind well-defined motifs within the β subunit cytoplasmic tail. We show that mice expressing β1 integrins with mutations that abrogate kindlin binding in the developing UB have mild medullary hypoplasia and a moderate branching defect. Collecting duct (CD) cells expressing the same mutations in the β1 subunit have moderate tubulogenesis, spreading and adhesion defects, but show intact growth factor-dependent signaling. In contrast, mice lacking kindlins in the UB are anephric due to a complete absence of UB budding. Kindlin-knockout CD cells are unable to spread, adhere or respond to growth factors, irrespective of whether the integrins are bound to a ligand. Thus, in addition to regulating integrin function, kindlins mediate crucial growth factor signaling required for initial UB formation.