title: Cell polarity regulator PARD6B is essential for trophectoderm formation in the preimplantation mouse embryo.
abstract: In preimplantation mouse development, the first cell lineages to be established are the trophectoderm (TE) and inner cell mass. TE possesses epithelial features, including apical-basal cell polarity and intercellular junctions, which are crucial to generate a fluid-filled cavity in the blastocyst. Homologs of the partitioning defective (par) genes in Caenorhabditis elegans are critical regulators of cell polarity. However, their roles in regulating TE differentiation and blastocyst formation remain unclear. Here, the role of mouse Pard6b, a homolog of par-6 gene and a component of the PAR-atypical protein kinase C (aPKC) complex, was investigated. Pard6b expression was knocked down by microinjecting RNA interference construct into zygotes. Pard6b-knockdown embryos cleaved and compacted normally but failed to form the blastocyst cavity. The cavitation failure is likely the result of defective intercellular junctions, because Pard6b knockdown caused abnormal distribution of actin filaments and TJP1 (ZO-1) tight junction (TJ) protein and interfered with cavitation in chimeras containing cells from normal embryos. Defective TJ formation may be caused by abnormal cell polarization, because the apical localization of PRKCZ (aPKCzeta) was absent in Pard6b-knockdown embryos. Pard6b knockdown also diminished the expression of CDX2, a TE-lineage transcription factor, in the outer cells. TEAD4, a transcriptional activator that is required for Cdx2 expression and cavity formation, was not essential for the transcription of Pard6b. Taken together, Pard6b is necessary for blastocyst morphogenesis, particularly the development of TE-specific features-namely, the apical-basal cell polarity, formation of TJ, paracellular permeability sealing, and up-regulated expression of Cdx2.
authors.affiliation: Institute for Biogenesis Research, Department of Anatomy, Biochemistry, and Physiology, John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii 96813, USA. vernadet@hawaii.edu
authors.forename: Vernadeth B
authors.initials: VB
authors.lastname: Alarcon
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001755:Blastocyst / Q000502:physiology*; D000071616:CDX2 Transcription Factor; D045744:Cell Line, Tumor; D019070:Cell Lineage; D016764:Cell Polarity / Q000502:physiology*; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D004847:Epithelial Cells / Q000502:physiology; D005455:Fluorescent Antibody Technique; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008845:Microinjections; D018613:Microscopy, Confocal; D009024:Morphogenesis / Q000502:physiology*; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000091262:TEA Domain Transcription Factors; D019108:Tight Junctions / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000071616:CDX2 Transcription Factor; C487514:Cdx2 protein, mouse; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D009124:Muscle Proteins; C518597:Par6 protein, mouse; D000091262:TEA Domain Transcription Factors; C101204:Tead4 protein, mouse; D014157:Transcription Factors; D011493:Protein Kinase C