EMBO Reports最新文献

Even before the advent of multicellular life, unicellular creatures would communicate with their neighbours to coordinate their behaviours. Multicellular organisms have the particular challenge of orchestrating the differentiation of stem and progenitor cells to generate and maintain coherent functional tissues. However, stem and progenitor cells face a problem: their differentiation response can be buffeted by oscillations or stochastic fluctuations in intrinsic regulators. This generates cell-to-cell variability, which can be further compounded when extrinsic cues don't provide clear unambiguous instructions. So, left to their own devices, cells may differentiate at different rates or different directions even in response to the same cues. Fortunately, cells in multicellular organisms are not left to their own devices: they continually sense and respond to the behaviours of their neighbours. Here I discuss when, where, and how stem and progenitor cells communicate to synchronise their response to differentiation cues. I highlight technical challenges in identifying such synchronisation mechanisms, and survey emerging technologies that may help overcome these challenges.

Motile cilia are evolutionarily conserved protrusions critical for motility and homeostasis. Their rhythmic movements require the central pair microtubules (CP-MTs). While the initial CP-MT assembly in mammals is mediated by WDR47 and microtubule minus-end-binding CAMSAPs, the mechanism by which CP-MTs are stabilized remains unclear. Here, we demonstrate that WDR47 coordinates JHY and SPEF1 to maintain the stability of mammalian CP-MTs. By generating a proximity interactome of WDR47, we identify a group of CP-MT-associated proteins, including SPEF1 and JHY. WDR47 enriches JHY and SPEF1 to the central lumen and tip of nascent cilia, whereas SPEF1 recruits WDR47 and JHY to CP-MTs through direct interactions. Jhy deficiency in mice preferentially disrupts distal CP-MTs, resulting in rotatory ciliary beats. Phylogenetic analyses suggest conserved functions of WDR47 and SPEF1 in protozoa and metazoans, as well as a role for JHY in animals with radial or bilateral body symmetry. We propose that JHY emerges to further reinforce CP-MTs, enabling the transition from switchable to fixed ciliary waveforms in metazoan evolution.

Actins are cytoskeletal proteins that are essential for multiple cellular processes. Mutations in the ACTB and ACTG1 genes, encoding the ubiquitous beta- and gamma-cytoskeletal actin isoforms, respectively, cause a broad spectrum of neurodevelopmental disorders, with microcephaly as the most frequent one. To investigate the pathogenesis underlying this cortical malformation, we studied patient-derived cerebral organoids from induced pluripotent stem cells of individuals with the Baraitser-Winter-CerebroFrontoFacial syndrome (BWCFF-S) carrying an ACTB/ACTG1 missense mutation. These organoids were reduced in size, showing a thinner ventricular zone (VZ) due to reduced VZ progenitor abundance. Strikingly, VZ progenitors in BWCFF-S cerebral organoids displayed a shift in the orientation of their cleavage plane from a predominantly vertical to a majoritarian horizontal orientation. The latter cleavage plane orientation is incompatible with increasing VZ progenitor abundance and instead promotes basal progenitor generation. Various cytoskeletal and morphological irregularities of BWCFF-S VZ progenitors, notably in the apical region, seemingly contribute to this change in cleavage plane orientation. Our results provide insight into the cell biological basis of the microcephaly associated with BWCFF-S caused by actin mutations.

Argonautes are ancient proteins with well-characterised functions in cell-autonomous gene regulation and genome defence, but less clear roles in non-cell-autonomous processes. Extracellular Argonautes have been reported across plants, animals and protozoa, yet their biochemical and functional properties remain elusive. Here, we demonstrate that an extracellular Argonaute (exWAGO) released by the rodent-infective nematode Heligmosomoides bakeri is detectable inside mouse cells during the natural infection. We show that exWAGO is released from H. bakeri in both vesicular and non-vesicular forms that have different resistances to proteolysis, different accessibilities to antibodies and associate with different subsets of secondary siRNAs. Using recombinant exWAGO protein, we demonstrate that non-vesicular exWAGO is internalised by mouse cells in vitro and that immunisation of mice with exWAGO confers partial protection against subsequent H. bakeri infection and generates antibodies that block exWAGO uptake into cells. Finally, we show that properties of exWAGO are conserved across Clade V nematodes that infect humans and livestock. Together, this work expands the context in which Argonautes function and illuminates an RNA-binding protein as a vaccine target for parasitic nematodes.

Mouse embryonic stem cells (mESCs), in addition to differentiating into the three germ layers, can reverse typical developmental trajectories, as exemplified by their ability to de-differentiate into 2-cell-like cells (2CLCs) that resemble the mammalian embryo during zygotic genome activation (ZGA). This unique property offers the opportunity to elucidate the molecular principles that govern the pre-implantation stages of mammalian development. Here, we dissect the functions of the chromatin repressor EHMT2, a candidate antagonist of the mESC-to-2CLC transition, by leveraging a multipurpose allele for acute protein depletion and efficient immunoprecipitation. Our experiments revealed distinct principles of EHMT2-mediated gene repression in mESCs based on specific chromatin binding patterns and protein co-factors. Most notably, EHMT2 directly represses large clusters of co-regulated gene loci that comprise a significant fraction of the 2CLC-specific transcriptome by initiating H3K9me2 spreading from distal LINE-1 elements. EHMT2 counteracts the recruitment of the activator DPPA2/4 to promoter-proximal endogenous retroviral elements (ERVs) at 2CLC genes. EHMT2 depletion enhances the expression of ZGA-associated transcripts in 2CLCs and synergizes with spliceosome inhibition and retinoic acid signaling to facilitate the mESC-to-2CLC transition. In contrast to ZGA-associated genes, the repression of germ layer-associated transcripts by EHMT2 occurs outside of gene clusters, in collaboration with ZFP462, and involves binding to non-repetitive candidate enhancers. Our observations provide novel mechanistic insight into how pluripotent cells achieve attenuation of their bidirectional differentiation potential and reveal unique transcriptional features of murine totipotent cells.

The choice between somatic and germline fates is essential for species survival. This choice occurs in embryonic epiblast cells, as these cells are competent for both somatic and germline differentiation. The transcription factor OTX2 regulates this process, as Otx2-null epiblast-like cells (EpiLCs) form primordial germ cell-like cells (PGCLCs) with enhanced efficiency. Yet, how OTX2 achieves this function is not fully characterised. Here we show that OTX2 controls chromatin accessibility at specific chromatin loci to enable somatic differentiation. CUT&RUN for OTX2 and ATAC-seq in wild-type and Otx2-null embryonic stem cells and EpiLCs identifies regions where OTX2 binds and opens chromatin. Enforced OTX2 expression maintains accessibility at these regions and also induces opening of ~4000 somatic-associated regions in cells differentiating in the presence of PGC-inducing cytokines. Once cells have acquired germline identity, these additional regions no longer respond to OTX2 and remain closed. Our results indicate that OTX2 works in cells with dual competence for somatic and germline differentiation to increase accessibility of somatic regulatory regions and induce the somatic fate at the expense of the germline.

During vertebrate neurogenesis, a transition from symmetric proliferative to asymmetric neurogenic divisions is critical to balance growth and differentiation. Using single-cell RNA-seq data from the chick embryonic neural tube, we identify the cell cycle regulator Cdkn1c as a key regulator of this transition. While Cdkn1 is classically associated with neuronal cell cycle exit, we show that its expression initiates at low levels in neurogenic progenitors. Functionally targeting the onset of this expression impacts the course of neurogenesis: Cdkn1c knockdown impairs neuron production by favoring proliferative symmetric divisions. Conversely, inducing a low-level Cdkn1c misexpression in self-expanding progenitors forces them to prematurely undergo neurogenic divisions. Cdkn1c exerts this effect primarily by inhibiting the CyclinD1-CDK4/6 complex and G1 phase lengthening. We propose that Cdkn1c acts as a dual driver of the neurogenic transition whose low level of expression first controls the progressive entry of progenitors into neurogenic modes of division before higher expression mediates cell cycle exit in daughter cells. This highlights that the precise control of neurogenesis regulators' expression sequentially imparts distinct functions essential for proper neural development.

During ovariogenesis, more than two-thirds of germ cells are sacrificed to improve the quality of the remaining oocytes. However, the detailed mechanisms behind this selection process are not fully understood in mammals. Here, we developed a high-resolution, four-dimensional ovariogenesis imaging system to track the progression of oocyte fate determination in live mouse ovaries. Through this, we identified a cyst-independent oocyte phagocytosis mechanism that plays a key role in determining oocyte survival. We found that oocytes act as individual cells, rather than connected cyst structures, during ovarian reserve construction. In this process, dominant oocytes capture and absorb cell debris from sacrificed oocytes to enrich their cytoplasm and support their survival. Single-cell sequencing indicated that the sacrificed oocytes are regulated by autophagy. When oocyte sacrifice was inhibited using autophagy inhibitors, the pool of surviving oocytes expanded, but they failed to fully develop and contribute to fertility. Our study suggests that mammals have evolved a cyst-independent selection system to improve oocyte quality, which is essential for sustaining a long reproductive lifespan.