The Role And Underlying Mechanism Of Surfeit Locus Protein 4(Surf4) In Somatic Cell Reprogramming

At present,somatic cell reprogramming research has achieved rapid development and profoundly altered the landscape in which stem cell research is conducted.However,compared with somatic cell nuclear transfer(SCNT)technology,transcription factors-mediated induced pluripotent stem cell technology(i PSC)is still inefficient and time-consuming.Lots of studies have indicated that mammalian oocytes possess fascinating unknown maternal factors,which have the ability to reprogram terminally differentiated germ cells(sperm)or somatic cells into totipotent embryos.In our previous study,we found that surfeit locus protein 4(Surf4),a maternal factor,can facilitate the generation of i PSCs,but the underlying mechanism remains unclear.The aim of our present study was to further clarify the role and mechanism of Surf4 in somatic cell reprogramming.We employed a reprogramming system based on the Doxcycline(Dox)-inducible expression of the four Yamanaka factors(Oct4,Sox2,Klf4 and c-Myc)and used mouse embryonic fibroblasts(MEFs)derived from Rosa26-M2 rt TA;Col1a1-4F2A;Oct4-GFP+ transgenic mice as starting cells.FACS analysis,alkaline phosphatase(AP)staining,q PCR and immunofluorescence(IF)staining were used to evaluate the efficiency of i PSCs derived from MEFs.Embryoid body(EB)and teratoma formation assays were performed to evaluate the differentiation ability of the i PSC lines.RNA-seq,q PCR and western blotting analysis were applied to investigate and validate the downstream targets of Surf4.When co-expressed with OSKM factors,Surf4 can significantly promote i PSC generation.The i PS cell lines induced by the overexpression of Surf4 can express the potency markers and most of the i PS cell lines had normal karyotypes.Furthermore,these i PS cell lines were able to differentiate into three germ layers through EB formation in vitro.They could also form teratomas consisting of cells from three germ layers in vivo.We further demonstrated that Surf4 was able to suppress the expression of genes related to cell cycle progression,alleviating the survival pressure caused by cell proliferation during reprogramming.Moreover,Surf4 can activate the endoplasmic reticulum stress(ER stress)response in the early stage of reprogramming.Both the endoplasmic reticulum chaperone Hspa5 and the active spliced form of Xbp1(s Xbp1)can mimic the promoting effect of Surf4 on reprogramming.Concordantly,blocking the unfolded protein response(UPR)attenuated the effect of Surf4 on reprogramming.Taken together,this study explored the role and underlying mechanism of Surf4 in the process of somatic cell-induced reprogramming.Our data revealed that Surf4 could facilitate somatic cell reprogramming by attenuating cell proliferation stress and activating the ER stress response,which provided a novel perspective for further understanding the molecular mechanism of somatic cell reprogramming,and also a new avenue for improving the efficiency of i PSC generation.