title: Sox2 is essential for formation of trophectoderm in the preimplantation embryo.
abstract: BACKGROUND
  In preimplantation mammalian development the transcription factor Sox2 (SRY-related HMG-box gene 2) forms a complex with Oct4 and functions in maintenance of self-renewal of the pluripotent inner cell mass (ICM). Previously it was shown that Sox2-/- embryos die soon after implantation. However, maternal Sox2 transcripts may mask an earlier phenotype. We investigated whether Sox2 is involved in controlling cell fate decisions at an earlier stage.
  
  
  RESULTS
  We addressed the question of an earlier role for Sox2 using RNAi, which removes both maternal and embryonic Sox2 mRNA present during the preimplantation period. By depleting both maternal and embryonic Sox2 mRNA at the 2-cell stage and monitoring embryo development in vitro we show that, in the absence of Sox2, embryos arrest at the morula stage and fail to form trophectoderm (TE) or cavitate. Following knock-down of Sox2 via three different short interfering RNA (siRNA) constructs in 2-cell stage mouse embryos, we have shown that the majority of embryos (76%) arrest at the morula stage or slightly earlier and only 18.7-21% form blastocysts compared to 76.2-83% in control groups. In Sox2 siRNA-treated embryos expression of pluripotency associated markers Oct4 and Nanog remained unaffected, whereas TE associated markers Tead4, Yap, Cdx2, Eomes, Fgfr2, as well as Fgf4, were downregulated in the absence of Sox2. Apoptosis was also increased in Sox2 knock-down embryos. Rescue experiments using cell-permeant Sox2 protein resulted in increased blastocyst formation from 18.7% to 62.6% and restoration of Sox2, Oct4, Cdx2 and Yap protein levels in the rescued Sox2-siRNA blastocysts.
  
  
  CONCLUSIONS
  We conclude that the first essential function of Sox2 in the preimplantation mouse embryo is to facilitate establishment of the trophectoderm lineage. Our findings provide a novel insight into the first differentiation event within the preimplantation embryo, namely the segregation of the ICM and TE lineages.
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.
authors.forename: Maria
authors.initials: M
authors.lastname: Keramari
authors.forename: Janet
authors.initials: J
authors.lastname: Razavi
authors.forename: Karen A
authors.initials: KA
authors.lastname: Ingman
authors.forename: Christoph
authors.initials: C
authors.lastname: Patsch
authors.forename: Frank
authors.initials: F
authors.lastname: Edenhofer
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Ward
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Kimber
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000235:genetics; D001755:Blastocyst / Q000166:cytology / Q000378:metabolism*; D000071616:CDX2 Transcription Factor; D018797:Cell Cycle Proteins; D002454:Cell Differentiation / Q000235:genetics; D019070:Cell Lineage / Q000235:genetics; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D053595:Embryonic Stem Cells / Q000166:cytology / Q000378:metabolism*; D005260:Female; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D018613:Microscopy, Confocal; D009028:Morula / Q000166:cytology / Q000378:metabolism; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D050814:Octamer Transcription Factor-3 / Q000235:genetics / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055748:SOXB1 Transcription Factors / Q000235:genetics / Q000378:metabolism*; D000091262:TEA Domain Transcription Factors; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014327:Trophoblasts / Q000166:cytology / Q000378:metabolism*; D000091102:YAP-Signaling Proteins
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000071616:CDX2 Transcription Factor; C487514:Cdx2 protein, mouse; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D009124:Muscle Proteins; D050814:Octamer Transcription Factor-3; D010750:Phosphoproteins; C494174:Pou5f1 protein, mouse; D012333:RNA, Messenger; D055748:SOXB1 Transcription Factors; C527783:Sox2 protein, mouse; D000091262:TEA Domain Transcription Factors; C101204:Tead4 protein, mouse; D014157:Transcription Factors; D000091102:YAP-Signaling Proteins; C486223:Yap1 protein, mouse