Selective assembly of connexin37 into heterocellular gap junctions at the oocyte/granulosa cell interface

Abstract

Studies of mice with targeted disruptions of specific connexin genes have revealed that at least two connexins, connexin37 (Cx37) and connexin43 (Cx43), play essential roles in ovarian follicle development. To explore the respective roles of these two connexins in gap-junctional communication between the developing murine oocyte and its surrounding cumulus granulosa cells, we used confocal immunofluorescence microscopy and oocyte preloading functional assays. Immunofluorescence microscopy located Cx37 within gap-junction plaques between granulosa cells and the oocyte, and Cx43 between surrounding granulosa cells. Preloading assays combining denuded oocytes and cultured granulosa cells expressing or lacking Cx37 or Cx43 revealed that Cx37 must be present in both cell types for the establishment of heterocellular gap-junctional coupling. Furthermore, immunofluorescence microscopy of cultured granulosa cells after incubation with denuded oocytes showed that the oocyte induces the formation of gap junctions containing Cx37 at the surface of granulosa cells. Continuous Cx37 expression in granulosa cells was confirmed using RT-PCR. Together, these results indicate that the growing murine oocyte is functionally coupled with granulosa cells by homotypic gap junctions composed of Cx37, and that the formation and/or stabilization of Cx37 junctions is selectively induced at the oocyte-granulosa interface by cell contact.

A Gja1 missense mutation in a mouse model of oculodentodigital dysplasia

“…Jrt mutants (Gittens et al, 2003;Veitch et al, 2004). In Gja1 Jrt /+ ϫ FVB ovaries, only a few scattered gap junction plaques were seen when compared with wild-type cells (+/+) (Fig.…”

Interplay between paracrine signaling and gap junctional communication in ovarian follicles

“…Each connexon is a hexamer of protein subunits, members of a family of homologous proteins called connexins (Cx). Several connexins are expressed in ovarian follicles and two in particular, Cx37 and Cx43, have been demonstrated to play essential roles in folliculogenesis (Veitch et al, 2004) (reviewed by Kidder and Mhawi, 2002). Cx37 is localized at the interface between the oocyte and surrounding granulosa cells from the primary follicle stage onward (Simon et al, 1997).…”

Cumulus cell contact during oocyte maturation in mice regulates meiotic spindle positioning and enhances developmental competence

“…Throughout oogenesis in mammals, oocytes maintain physical contact with follicular somatic cells via granulosa cell extensions known as transzonal projections (TZPs) [1,6,23,33,43,44]. Despite the recognized functions of TZPs in gap junction mediated metabolite exchange, heterocellular adhesion, cell cycle regulation and bidirectional signaling [10,18,40,47], the precise role these structures play in the acquisition of developmental competence during oocyte maturation is unknown. It is known that the majority of mammalian oocytes develop in situ with an eccentrically positioned germinal vesicle (GV) that may facilitate retention of maternal transcripts and essential organelles by excluding these components from the developing spindle [2], Interestingly, in rodent species, the GV has been shown to lose an eccentric position after culture [38,39] and That has been proposed to be a result of a loss in cortical stability secondary to precocious TZP retraction.…”