title: Allocation of inner cells to epiblast vs primitive endoderm in the mouse embryo is biased but not determined by the round of asymmetric divisions (8→16- and 16→32-cells).
abstract: The epiblast (EPI) and the primitive endoderm (PE), which constitute foundations for the future embryo body and yolk sac, build respectively deep and surface layers of the inner cell mass (ICM) of the blastocyst. Before reaching their target localization within the ICM, the PE and EPI precursor cells, which display distinct lineage-specific markers, are intermingled randomly. Since the ICM cells are produced in two successive rounds of asymmetric divisions at the 8→16 (primary inner cells) and 16→32 cell stage (secondary inner cells) it has been suggested that the fate of inner cells (decision to become EPI or PE) may depend on the time of their origin. Our method of dual labeling of embryos allowed us to distinguish between primary and secondary inner cells contributing ultimately to ICM. Our results show that the presence of two generations of inner cells in the 32-cell stage embryo is the source of heterogeneity within the ICM. We found some bias concerning the level of Fgf4 and Fgfr2 expression between primary and secondary inner cells, resulting from the distinct number of cells expressing these genes. Analysis of experimental aggregates constructed using different ratios of inner cells surrounded by outer cells revealed that the fate of cells does not depend exclusively on the timing of their generation, but also on the number of cells generated in each wave of asymmetric division. Taking together, the observed regulatory mechanism adjusting the proportion of outer to inner cells within the embryo may be mediated by FGF signaling.
authors.affiliation: Department of Embryology, Faculty of Biology, University of Warsaw, Miecznikowa 1, 02-096 Warsaw, Poland.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Krupa
authors.forename: Ewa
authors.initials: E
authors.lastname: Mazur
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Szczepańska
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Filimonow
authors.forename: Marek
authors.initials: M
authors.lastname: Maleszewski
authors.forename: Aneta
authors.initials: A
authors.lastname: Suwińska
mesh_terms: D000818:Animals; D053624:Blastocyst Inner Cell Mass / Q000166:cytology / Q000378:metabolism*; D002454:Cell Differentiation; D002455:Cell Division / Q000502:physiology*; D019070:Cell Lineage / Q000235:genetics; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism*; D004707:Endoderm / Q000166:cytology / Q000196:embryology* / Q000254:growth & development; D005260:Female; D051519:Fibroblast Growth Factor 4 / Q000096:biosynthesis / Q000378:metabolism; D050993:GATA6 Transcription Factor / Q000096:biosynthesis; D018398:Homeodomain Proteins / Q000096:biosynthesis; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D000071317:Nanog Homeobox Protein; D050814:Octamer Transcription Factor-3 / Q000096:biosynthesis; D051497:Receptor, Fibroblast Growth Factor, Type 2 / Q000096:biosynthesis / Q000378:metabolism; D055748:SOXB1 Transcription Factors / Q000096:biosynthesis; D015398:Signal Transduction; D014327:Trophoblasts / Q000166:cytology / Q000378:metabolism*
chemical_list: C496446:Fgf4 protein, mouse; D051519:Fibroblast Growth Factor 4; D050993:GATA6 Transcription Factor; C494760:Gata6 protein, mouse; D018398:Homeodomain Proteins; D000071317:Nanog Homeobox Protein; C475540:Nanog protein, mouse; D050814:Octamer Transcription Factor-3; C494174:Pou5f1 protein, mouse; D055748:SOXB1 Transcription Factors; C527783:Sox2 protein, mouse; C496354:Fgfr2 protein, mouse; D051497:Receptor, Fibroblast Growth Factor, Type 2
keywords: Asymmetric division; Epiblast; Fgf/MAP kinase pathway; Mouse blastocyst; Primitive endoderm