title: Xenopus Nanos1 is required to prevent endoderm gene expression and apoptosis in primordial germ cells.
abstract: Nanos is expressed in multipotent cells, stem cells and primordial germ cells (PGCs) of organisms as diverse as jellyfish and humans. It functions together with Pumilio to translationally repress targeted mRNAs. Here we show by loss-of-function experiments that Xenopus Nanos1 is required to preserve PGC fate. Morpholino knockdown of maternal Nanos1 resulted in a striking decrease in PGCs and a loss of germ cells from the gonads. Lineage tracing and TUNEL staining reveal that Nanos1-deficient PGCs fail to migrate out of the endoderm. They appear to undergo apoptosis rather than convert to normal endoderm. Whereas normal PGCs do not become transcriptionally active until neurula, Nanos1-depleted PGCs prematurely exhibit a hyperphosphorylated RNA polymerase II C-terminal domain at the midblastula transition. Furthermore, they inappropriately express somatic genes characteristic of endoderm regulated by maternal VegT, including Xsox17α, Bix4, Mixer, GATA4 and Edd. We further demonstrate that Pumilio specifically binds VegT RNA in vitro and represses, along with Nanos1, VegT translation within PGCs. Repressed VegT RNA in wild-type PGCs is significantly less stable than VegT in Nanos1-depleted PGCs. Our data indicate that maternal VegT RNA is an authentic target of Nanos1/Pumilio translational repression. We propose that Nanos1 functions to translationally repress RNAs that normally specify endoderm and promote apoptosis, thus preserving the germline.
authors.affiliation: Department of Cell Biology, University of Miami School of Medicine, 1011 NW 15th St, Miami, FL 33136, USA.
authors.forename: Fangfang
authors.initials: F
authors.lastname: Lai
authors.forename: Amar
authors.initials: A
authors.lastname: Singh
authors.forename: Mary Lou
authors.initials: ML
authors.lastname: King
mesh_terms: D000818:Animals; D017209:Apoptosis; D004707:Endoderm / Q000166:cytology / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D017930:Genes, Reporter; D005854:Germ Cells / Q000166:cytology*; D017403:In Situ Hybridization; D008856:Microscopy, Fluorescence / Q000379:methods; D008954:Models, Biological; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000378:metabolism / Q000502:physiology*; D029867:Xenopus Proteins / Q000378:metabolism / Q000502:physiology*; D014982:Xenopus laevis
chemical_list: D012097:Repressor Proteins; D029867:Xenopus Proteins; C558784:nanos1 protein, Xenopus