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Repression of an activity-dependent autocrine insulin signal is required for sensory neuron development in C. elegans

ABSTRACT: The nervous system comprises diverse and highly specialized neuron-types, each expressing a unique set of genes that defines its functional properties. What molecular mechanisms generate diverse neuron types remains a central question in neuroscience. Our study of C. elegans chemosensory BAG neurons showed that a p38 MAP kinase (MAPK), PMK-3, is required for their proper differentiation and function (Brandt, J. and Ringstad, N. 2015). How p38 MAPKs function in neurodifferentiation is poorly understood. To better understand how pmk-3 promotes the BAG cell fate, we purified wild-type and pmk-3 mutant chemosensory BAG neurons and determined their transcriptomes using RNA-Seq. Expression of a number of genes that encode neuropeptides, including insulin-like peptides (ILPs), were up-regulated in pmk-3 mutant BAG neurons. Through analysis of mutations that restore expression of a BAG-fate marker to pmk-3 mutants, we additionally found that genes required for the release of neuropeptides, including UNC-31/CAPS, suppress pmk-3 mutant gene expression defects. These two observations suggested that the differentiation defects of pmk-3 mutants are associated with dysregulated release of peptide hormones. Indeed, we find that increased synthesis and release of ILPs from BAG during development causes a significant fraction of the gene expression and functional defects of pmk-3 mutant neurons. Together our data delineate a mechanism through which p38 MAPKs promote proper sensory neuron differentiation by inhibiting an autocrine insulin signal that represses expression of a BAG neuron fate. These findings reveal an unexpected role for insulin signaling in nervous system development and suggest that insulin-like factors are at the nexus of intrinsic genetic programs and extrinsic signaling mechanisms that regulate cell fate and neuronal differentiation.

ORGANISM(S): Caenorhabditis elegans

PROVIDER: GSE137267 | GEO | 2019/09/12

REPOSITORIES: GEO

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Project description:p38-MAPKs are stress activated kinases necessary for placental development and nutrient and oxygen transfer during murine post-implantation development. In preimplantation development, p38-MAPK activity is required for blastocyst formation. Additionally, we have previously reported its role in regulating specification of inner cell mass (ICM) towards primitive endoderm (PrE), although a comprehensive mechanistic understanding is currently limited. Adopting live embryo imaging, proteomic and transcriptomic approaches, we report experimental data that directly address this deficit. Chemical inhibition of p38-MAPK activity during blastocyst maturation causes impaired blastocyst cavity expansion, most evident between the third and tenth hours post inhibition onset. We identify an overlapping minimal early blastocyst maturation window of p38-MAPKi inhibition (p38-MAPKi) sensitivity, that is sufficient to impair PrE cell fate by the late blastocyst (E4.5) stage. Comparative proteomic analyses reveal substantial downregulation of ribosomal proteins, the mRNA transcripts of which are also significantly upregulated. Ontological analysis of the differentially expressed transcriptome during this developmental period reveals “translation” related gene transcripts as being most significantly, yet transiently, affected by p38-MAPKi. Moreover, combined assays consistently report concomitant reductions in de novo translation that are associated with accumulation of unprocessed rRNA precursors. Using a phospho-proteomic approach, ± p38-MAPKi, to potentially identify p38-MAPK effectors, we report that clonal siRNA mediated knockdown of Mybpp1a, an rRNA transcription and processing regulator gene, is associated with significantly diminished PrE contribution. Lastly, we show that defective PrE specification caused by p38-MAPKi (but not MEK/ERK signalling inhibition) can be partially rescued by activating the archetypal mTOR mediated translation regulatory pathway. Activated p38-MAPK controls blastocyst maturation in an early and distinctly transient developmental window by regulating gene functionalities related to translation, that creates a permissive environment for appropriate specification of ICM cell fate.

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Repression of an activity-dependent autocrine insulin signal is required for sensory neuron development in C. elegans

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