Major loss of junctional coupling during mitosis in early mouse embryos.

Abstract

Abstract. Junctional coupling was assessed during the transition from the fourth to the fifth cell cycle of mouse embryogenesis by injection of the dye carboxyfluorescein and by measurement of electrical continuity between cells. Junctional coupling, which arises de novo in early 8-cell mouse embryos, subsequently becomes reduced towards the end of the cell cycle as the blastomeres enter into mitosis. Arrest of the cell cycle in metaphase by nocodazole, an inhibitor of tubulin polymerization, reveals that cell coupling becomes undetectable at mitosis. Junctional coupling then is resumed during interphase of the 16-cell stage. Nocodazole itself has no effect on junctional coupling in interphase cells, regardless of the extent of intercellular flattening, whereas taxol, a microtubule-stabilizing agent, does reduce the extent of coupling in interphase cells.

CX43 expression, phosphorylation, and distribution in the normal and autoimmune orchitic testis with a look at gap junctions joining germ cell to germ cell

“…Our observation is consistent with the localization of Cx43 mRNA to primary spermatocytes (72) and spermatogonia (6,9,72). Our observation of low Cx43 mRNA and protein levels during the two spermatogonial stem cell proliferation periods is in line with the concept that the cells' ability to communicate through gap junctions is inversely related to their growth activity (70,71), with the mitotic cells being weakly coupled among themselves, and with other in- terphasic cells in most systems (24,48). Our observation is in agreement with the report that early-stage germ cells proliferated in Cx43 knockout testicular grafts (69) and with the finding that the conditional knockout of Cx43 solely in Sertoli cells allowed proliferation of early spermatogonia but not the completion of spermatogenesis (11,76).…”

Gap junction assembly in the preimplantation mouse conceptus is independent of microtubules, microfilaments, cell flattening, and cytokinesis.

“…In this respect our results are comparable to those of Salas et al (23), who found that targeting of viral proteins to specific plasma membrane domains in MDCK cells does not depend on intact microtubules or actin microfilaments. Another interesting finding from our experiments with nocodazole is that, unlike late eight-cell blgstomeres, which uncouple from one another when blocked in mitosis (24), four-cell embryos prevented from undergoing mitosis can initiate gap junction assembly after reaching the proper age. Thus, the initiation of gap junction assembly must be independent of the preceding mitosis, whereas the maintenance of intercellular coupling via existing gap junctions later on in that and succeeding cell cycles is directly dependent on the mitotic cycle.…”

Position- and polarity-dependent Hippo signaling regulates cell fates in preimplantation mouse embryos

“…Thus, cell fates are controlled by the differential inheritance of determinants caused by cell polarization. In support of this model, it has been demonstrated that, although polarization of the cytoplasm and cytoskeleton [40] and most junctional contacts between cells [41] are lost during the division of dissociated blastomeres of 8-cell embryos (1/8 cells), the polarized organization of the apical cortical domain is maintained [42] and the daughter cells differentially inheriting apical domains produce 2/16 couplets of polar TE and apolar ICM cells [16,42].…”