title: Par-aPKC-dependent and -independent mechanisms cooperatively control cell polarity, Hippo signaling, and cell positioning in 16-cell stage mouse embryos.
abstract: In preimplantation mouse embryos, the Hippo signaling pathway plays a central role in regulating the fates of the trophectoderm (TE) and the inner cell mass (ICM). In early blastocysts with more than 32 cells, the Par-aPKC system controls polarization of the outer cells along the apicobasal axis, and cell polarity suppresses Hippo signaling. Inactivation of Hippo signaling promotes nuclear accumulation of a coactivator protein, Yap, leading to induction of TE-specific genes. However, whether similar mechanisms operate at earlier stages is not known. Here, we show that slightly different mechanisms operate in 16-cell stage embryos. Similar to 32-cell stage embryos, disruption of the Par-aPKC system activated Hippo signaling and suppressed nuclear Yap and Cdx2 expression in the outer cells. However, unlike 32-cell stage embryos, 16-cell stage embryos with a disrupted Par-aPKC system maintained apical localization of phosphorylated Ezrin/Radixin/Moesin (p-ERM), and the effects on Yap and Cdx2 were weak. Furthermore, normal 16-cell stage embryos often contained apolar cells in the outer position. In these cells, the Hippo pathway was strongly activated and Yap was excluded from the nuclei, thus resembling inner cells. Dissociated blastomeres of 8-cell stage embryos form polar-apolar couplets, which exhibit different levels of nuclear Yap, and the polar cell engulfed the apolar cell. These results suggest that cell polarization at the 16-cell stage is regulated by both Par-aPKC-dependent and -independent mechanisms. Asymmetric cell division is involved in cell polarity control, and cell polarity regulates cell positioning and most likely controls Hippo signaling.
authors.affiliation: Department of Cell Fate Control, Institute of Molecular Embryology and Genetics, Kumamoto University, 2-2-1 Honjo, Chuo-ku, Kumamoto, 860-0811, Japan.
authors.forename: Yoshikazu
authors.identifier: http://orcid.org/0000-0001-9116-3603
authors.initials: Y
authors.lastname: Hirate
authors.affiliation: Laboratory for Embryonic Induction, RIKEN Center for Developmental Biology, 2-2-3 Minatojima-minamimachi, Chuo-ku, Kobe, Hyogo, 650-0047, Japan.
authors.forename: Shino
authors.initials: S
authors.lastname: Hirahara
authors.affiliation: Animal Resource Development Unit, Division of Bio-function Dynamics Imaging, RIKEN Center for Life Science Technologies, 2-2-3 Minatojima-minamimachi, Chuo-ku, Kobe, Hyogo, 650-0047, Japan.
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Inoue
authors.affiliation: Animal Resource Development Unit, Division of Bio-function Dynamics Imaging, RIKEN Center for Life Science Technologies, 2-2-3 Minatojima-minamimachi, Chuo-ku, Kobe, Hyogo, 650-0047, Japan.|Genetic Engineering Team, Division of Bio-function Dynamics Imaging, RIKEN Center for Life Science Technologies, 2-2-3 Minatojima-minamimachi, Chuo-ku, Kobe, Hyogo, 650-0047, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kiyonari
authors.affiliation: Laboratory for Pluripotent Cell Studies, RIKEN Center for Developmental Biology, 2-2-3 Minatojima-minamimachi, Chuo-ku, Kobe, Hyogo, 650-0047, Japan.|Department of Stem Cell Biology, Institute of Molecular Embryology and Genetics, Kumamoto University, 2-2-1 Honjo, Chuo-ku, Kumamoto, 860-0811, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Niwa
authors.affiliation: Department of Cell Fate Control, Institute of Molecular Embryology and Genetics, Kumamoto University, 2-2-1 Honjo, Chuo-ku, Kumamoto, 860-0811, Japan.|Laboratory for Embryogenesis, Graduate School of Frontier BioSciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sasaki
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000166:cytology / Q000378:metabolism; D001757:Blastomeres / Q000166:cytology / Q000378:metabolism; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D016764:Cell Polarity / Q000235:genetics / Q000502:physiology*; D004622:Embryo, Mammalian / Q000166:cytology* / Q000378:metabolism*; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000235:genetics / Q000502:physiology; D000090683:Hippo Signaling Pathway; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D011247:Pregnancy; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology
chemical_list: D018398:Homeodomain Proteins; D017346:Protein Serine-Threonine Kinases; D011493:Protein Kinase C
keywords: Hippo signaling; Par-aPKC; asymmetric cell division; cell polarity; preimplantation embryo