The Role And Mechanism Of RNA-binding Protein PUF Family In Mouse Growth And Early Embryonic Development

RNA-binding proteins(RBPs)are proteins that bind RNAs in the form of ribonucleoproteins complex(RNP complex)via structure motif(s).They often function by regulating RNA splicing and transport,mRNA stability and translation or other vital cellular processes.The genetic information must be faithfully delivered first from DNA to RNA,then from RNA to protein,eventually to particular characters and phenotypes.Recent studies revealed information flow from RNA to protein is not automatic,instead highly regulated temporally and spatially.Thus,the regulation of RNA expression,also called post-transcriptional regulation,plays a significant role in the maintenance of cell functions and the life of organism.PUF(PUMILIO and FBF)family is a widespread and evolutionarily highly conserved RNA-binding protein family in eukaryotes.Previous study reported that post-transcriptional regulation via PUF family plays key roles in embryogenesis,germ stem cell maintenance and gametogenesis in invertebrates(Drosophila and C.elegans).Mouse Puml has been previously identified to safeguard spermatogenesis and to inhibit neurodegeneration.Loss of Pum2 also causes abnormal behaviors.However,physiological functions and molecular mechanism of the Pum1 and Pum2 are still little known in the mammals.Here,we report that Pum1 and Pum2,which encode highly conserved PUF RNA-binding proteins,regulate mouse body and organ size by posttranscriptional repression of the cell cycle inhibitor CDKNlb.Binding of PUM1 or PUM2 to Pumilio Binding Elements(PBE)in the 3' UTR of Cdkn1b inhibits translation,promoting G1-S transition and cell proliferation.Mice with null mutations in Pum1and Pum2 exhibit gene dosage-dependent reductions in body and organ size,and deficiency for Cdknlb partially rescued postnatal growth defects in Pum1-/-mice.We propose that coordinated tissue-specific expression of Puml and Pum2,which involves autoregulatory and reciprocal posttranscriptional repression,contributes to the precise regulation of body and organ size.On the other hand,Puml and Pum2 double knockout mice showed embryonic lethality and embryos died before E8.5.Compared with wildtype,Pum1-/-;Pum2-/-ESCs exhibit reduced cell growth,accumulation of G1 phase cells and decreased self-renewal.Loss of Pum1 and Pum2 led to ESCs spontaneous differentiation into endoderm lineage in the presence of LIF,indicating an essential role of PUF family in the proliferation and stem maintenance in ESCs.In summary,Our data argued that PUM family mediated posttranscriptional control of cell cycle regulators represented a novel paradigm in the genetic control of body size and embryonic stem cell fate decision that warrants further exploration.