Development最新文献

cAMP-PKA signaling initiates the crucial process of oocyte meiotic maturation in many animals, but inhibits it in vertebrates. To address this 'cAMP paradox', we exchanged the key PKA substrate ARPP19 between representative species, the vertebrate Xenopus and the cnidarian Clytia, comparing its phosphorylation and function. We found that, as in Xenopus, Clytia maturing oocytes undergo ARPP19 phosphorylation on a highly conserved Gwl site, which inhibits PP2A and promotes M-phase entry. In contrast, despite a PKA phosphorylation signature motif recognizable across most animals, Clytia ARPP19 was only poorly phosphorylated by PKA in vitro and in vivo. Furthermore, unlike Xenopus ARPP19, exogenous Clytia ARPP19 did not delay Xenopus oocyte maturation. We conclude that, in Clytia, ARPP19 does not intervene in oocyte maturation initiation because of both poor recognition by PKA and the absence of effectors that mediate vertebrate oocyte prophase arrest. We propose that ancestral ARPP19 phosphorylated by Gwl has retained a key role in M-phase across eukaryotes and has acquired new functions during animal evolution mediated by enhanced PKA phosphorylation, allowing co-option into oocyte maturation regulation in the vertebrate lineage.

The role of anti-WNT ZNRF3 is central to determining gonadal fate: XY mice lacking functional ZNRF3 exhibit a highly variable gonadal sex reversal phenotype in the fetal period, characterised by appearance of ovarian tissue. To investigate this sex reversal further, we used single-cell RNA-seq to examine the transcriptomes of XY Znrf3-deficient gonads during the mouse sex-determining period. Analyses of cell trajectories in mutant gonads reveal the failure of pre-supporting cells to commit to the Sertoli cell fate, XY granulosa cell development, unstable commitment in those cells that reach the Sertoli path and enhanced contribution to a supporting-like cell fate. By developing a machine learning-based score for transcriptomic similarity to Sertoli and granulosa, we show pervasive disruption to acquisition of testicular cell fate in the mutant supporting cell lineage, with large numbers of cells co-expressing pro-Sertoli and pro-granulosa markers. These data reveal that loss of Znrf3 results in transcriptomic and cellular heterogeneity, with shifts in cellular sex identity that undermine a simple binary model in which mutant supporting cell precursors achieve either Sertoli or granulosa cell differentiation.

How multipotent progenitors give rise to multiple cell types in defined numbers is a central question in developmental biology. Epigenetic switches, acting at single gene loci, can generate extended delays in the activation of lineage-specifying genes and impact lineage decisions and cell type output. Here, we analyzed a timed epigenetic switch controlling expression of mouse Bcl11b, a transcription factor that drives T-cell commitment, but only after a multi-day delay. To investigate roles for this delay in controlling lineage decision making, we analyzed progenitors with a deletion in a distal Bcl11b enhancer, which extends this delay by ∼3 days. Strikingly, delaying Bcl11b activation reduces T-cell output but enhances innate lymphoid cell (ILC) generation in the thymus by redirecting uncommitted progenitors to the ILC lineages. Mechanistically, delaying Bcl11b activation promoted ILC redirection by enabling upregulation of the ILC-specifying transcription factor PLZF. Despite the upregulation of PLZF, committed ILC progenitors could subsequently express Bcl11b, which is also needed for type 2 ILC differentiation. These results show that epigenetic switches can control the activation timing and order of lineage-specifying genes to modulate cell type numbers and proportions.

It has been shown that 5-methylcytosine (m5C), one of the most abundant modifications on RNA, regulates various biological processes. However, the function of m5C modification in the nervous system is still largely unknown. Here, we show that the m5C reader Ybx1 is highly expressed in the developing mouse hippocampus in the central nervous system (CNS). Conditional knockout of Ybx1 in the dentate gyrus (DG) decreases mossy fiber growth and affects short-term memory. In the peripheral nervous system (PNS), the mRNA of Ybx1 is enriched in the axons of dorsal root ganglion (DRG) neurons and can be locally translated. Inhibition of local translation of Ybx1 results in a decrease in axon growth. We further identify 28 target mRNAs of Ybx1 in DRG neurons, including Ttl and Mmp24. Axon-specific knockdown of Ttl and Mmp24 decreases axon growth rate both in DRG and DG. It could be a general mechanism that locally translated Ybx1 regulates axon growth by controlling local translation in both CNS and PNS.

The protocadherins Fat and Dachsous regulate organ growth, shape, patterning, and planar cell polarity. Although Dachsous and Fat have been described as ligand and receptor, respectively, in a signal transduction pathway, there is also evidence for bidirectional signaling. Here, we assess signaling downstream of Dachsous through analysis of its intracellular domain. Genomic deletions of conserved sequences within dachsous identified regions of the intracellular domain that contribute to Dachsous activity. Deletion of the A motif increased Dachsous protein levels and decreased wing size. Deletion of the D motif decreased Dachsous levels at cell membranes, increased wing size, and disrupted wing, leg and hindgut patterning and planar cell polarity. Co-immunoprecipitation experiments established that the D motif is necessary and sufficient for association of Dachsous with key partners, including Lowfat, Dachs, Spiny-legs, Fat and MyoID. Subdivision of the D motif identified distinct regions that preferentially contribute to different Dachsous activities. Our results identify motifs that are essential for Dachsous function and are consistent with the hypothesis that the key function of Dachsous is regulation of Fat.

Synaptogenesis involves the transformation of dendritic filopodial contacts into stable connections with the exact apposition of synaptic components. Signalling triggered by Wnt/β-catenin and calcium has been postulated to aid this process. However, it is unclear how such a signalling process orchestrates synapse formation to organise the spatial arrangement of synapses along dendrites. We show that WNT7A is loaded on dynamic dendritic filopodia during spine formation in human cortical neurons. WNT7A is present at the tips of the filopodia and the contact sites with dendrites of neighbouring neurons, triggering spatially restricted localisation of the Wnt co-receptor LRP6. Here, we demonstrate that WNT7A at filopodia tips leads to the induction of calcium transients, the clustering of pre- and postsynaptic proteins, and the subsequent transformation into mature spines. Although soluble WNT7A protein can also support synaptogenesis, it fails to provide this degree of spatial information for spine formation and calcium transients, and synaptic markers are induced ectopically along the dendrites. Our data suggest that dendritic filopodia are WNT7A-bearing cytonemes required for focal calcium signalling and initiation of synapse formation, and provide an elegant mechanism for orchestrating the positioning of synapses along dendrites.

Macrophage-like cells called haemocytes are key effectors of Drosophila cellular innate immune function. Larval haemocytes exist either in circulation or localize to segmentally repeated sessile haemocyte compartments (SHCs). While numerous functions have been proposed for SHCs, the mechanisms directing haemocytes to them are unclear. Here, we have exploited the developmentally regulated dispersal of SHCs that occurs at pupariation to identify the Abrupt (Ab) transcription factor (TF) and ninjurin cell-adhesion molecules as regulators of haemocyte recruitment to SHCs. We show that larval haemocytes express ninjurins, which are required for targeting haemocytes to SHCs. However, at pupariation, ecdysteroid signalling stimulates Ab expression, which collaborates with TFs, including Blimp-1 and Hr3, to repress ninjurins and disperse haemocytes. We observe that experimental manipulations that antagonize ninjurin function in larval haemocytes cause premature SHC dispersal, while stabilization of ninjurins in haemocytes blocks developmentally regulated SHC remodelling and increases sensitivity to immune challenges. Cumulatively, our data indicate that control of ninjurin activity provides a common target through which diverse developmental, environmental and immune stimuli can be integrated to control haemocyte dispersal and immune function.

During embryonic development, muscle tissues, skin, and a subset of vascular endothelial cells arise from Pax3-expressing embryonic progenitors defined as paraxial mesoderm. By contrast, haemogenic potential is well established for extra-embryonic mesoderm and intra-embryonic lateral plate mesoderm, which do not express Pax3. To date, it is not known whether the haematopoietic system also contains Pax3 lineage cells. Here, we show that the mouse foetal liver and foetal circulation contain a transient population of Pax3 lineage cells with hallmarks of haematopoietic progenitors and the potential to generate both myeloid and erythroid cells. We propose that Pax3 lineage haematopoietic cells should be investigated to better understand normal haematopoietic development from different mesodermal derivatives. Further, genetic alterations of Pax3 lineage haematopoietic cells should be investigated for their potential to cause haematopoietic malignancies.

Meristems are three-dimensional (3D) generative structures that contain stem cells and produce new organs and tissues. Meristems develop in all land plants; however we know little about the spatial and temporal regulation of meristem structure in lineages such as bryophytes. Here, we describe the 3D meristem anatomy during the development of the liverwort Marchantia polymorpha. We show that the apical stem cell of the mature meristem is sub-apical, ventral, and in the outer cell layer. Mature meristem anatomy is therefore asymmetrical in the dorsoventral axis, which is reflected by the domain-specific protein localisation of Class III and Class IV Homeodomain-Leucine-Zippers (MpC3HDZ and MpC4HDZ), and by the promoter activity of MpYUCCA2. The dorsoventral asymmetry that defines the mature meristem is absent in the juvenile meristems of asexual propagules known as gemmae. We discovered that anatomical dorsoventral asymmetry of the meristem forms after 1 to 2 days of gemmaling growth, and is accompanied by expression of the dorsal identity reporter MpC3HDZ. We conclude that the gemma meristem has arrested development and undergoes anatomical rearrangement to develop the 3D meristem structure of the mature plant.