title: PUF-8 negatively regulates RAS/MAPK signalling to promote differentiation of C. elegans germ cells.
abstract: Signals that promote germ cell self-renewal by preventing premature meiotic entry are well understood. However, signals that control mitotic proliferation to promote meiotic differentiation have not been well characterized. In Caenorhabditis elegans, GLP-1 Notch signalling promotes the proliferative fate by preventing premature meiotic entry. The germline niche cell, which is the source of the ligand for GLP-1, spatially restricts GLP-1 signalling and thus enables the germ cells that have moved away from the niche to enter meiosis. Here, we show that the suppression of RAS/MAP kinase signalling in the mitotic and meiotic-entry regions is essential for the regulation of the mitosis-meiosis switch by niche signalling. We provide evidence that the conserved PUF family RNA-binding protein PUF-8 and the RAS GAP protein GAP-3 function redundantly to suppress the LET-60 RAS in the mitotic and meiotic entry regions. Germ cells missing both PUF-8 and GAP-3 proliferate in an uncontrolled fashion and fail to undergo meiotic development. MPK-1, the MAP kinase downstream of the LET-60 RAS, is prematurely activated in these cells; downregulation of MPK-1 activation eliminates tumours and restores differentiation. Our results further reveal that PUF-8 negatively regulates LET-60 expression at a post-transcriptional step. LET-60 is misexpressed in the puf-8(-) mutant germlines and PUF-8 physically interacts with the let-60 3' UTR. Furthermore, PUF-8 suppresses let-60 3' UTR-mediated expression in the germ cells that are transitioning from the mitotic to meiotic fate. These results reveal that PUF-8-mediated inhibition of the RAS/MAPK pathway is essential for mitotic-to-meiotic fate transition.
authors.affiliation: Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur, India.
authors.forename: Samir
authors.initials: S
authors.lastname: Vaid
authors.forename: Mohd
authors.initials: M
authors.lastname: Ariz
authors.forename: Amaresh
authors.initials: A
authors.lastname: Chaturbedi
authors.forename: Ganga Anil
authors.initials: GA
authors.lastname: Kumar
authors.forename: Kuppuswamy
authors.initials: K
authors.lastname: Subramaniam
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D017173:Caenorhabditis elegans / Q000196:embryology*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology*; D024202:Electrophoretic Mobility Shift Assay; D005854:Germ Cells / Q000502:physiology*; D047468:Immunoprecipitation; D008856:Microscopy, Fluorescence; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D016296:Mutagenesis; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D029742:Caenorhabditis elegans Proteins; C510538:PUF-8 protein, C elegans; D016601:RNA-Binding Proteins; C066646:let-60 protein, C elegans; D019950:Mitogen-Activated Protein Kinase 1; C085697:mpk-1 protein, C elegans; D018631:ras Proteins