Gap junctions between the oocyte and companion follicle cells in the mammalian ovary.

Abstract

The physical basis for communication between animal cells is thought largely to depend on the presence of gap junctions which are wide-spread among various vertebrate and invertebrate tissues (14,20). Studies on cultured cell lines have indicated that, in addition to mediating electrical impulse propagation between neighboring cells (electrotonic coupling), gap junctions mediate certain metabolic aspects of cellular function by permitting the transcellular passage of "informational" cytoplasmic molecules between physically conjoined cells (metabolic cooperation) (10,15,23). Moreover, the morphological demonstration that gap junctions conjoin different cell types within tissues such as the vertebrate retina (19), an arachnid midgut (16), and the mammalian kidney (18) establishes a precedent for gap junction-mediated cooperation between distinct cell types in other tissues.Recent physiological findings (3, 13) suggest that metabolic cooperativity between folliculargranulosa cells and oocytes within developing mammalian ovarian follicles may importantly regulate both the meiotic maturation of the egg and the transformation of the follicular epithelium into the corpus luteum. As an extension of our studies into the nature of coordinative cellular interactions in the ovarian follicle (2), we report here that gap junctions conjoin oocytes to companion follicular cells. MATERIALS AND METHODS Thin Section and Tracer AnalysisOvaries from adult cycling female mice, rats, and rhesus monkeys (Macaca mulatta), from 1-and 5-6-day old rats and from estrous rabbits were fixed for freezefracture studies by immersion for 20 rain at room temperature in 0.1 M cacodylate buffer (pH 7.4) containing 2% paraformaldehyde, 3% glutaraldehyde, and 5% sucrose. Thin-section and tracer samples were fixed for a total of 60 rain. Final fixation in all cases was carried out on individual follicles which had been dissected free from surrounding stromal tissue (with the exception of the 5-6-day-old rat ovaries) and cut into l-ram cubes. Better fixation of rabbit follicles from animals in estrous was achieved by omitting the paraformaldehyde from the primary fixative,. Ionic lanthanum was used as an extracellular tracer as previously described (2). After several washes in buffer, the tissues were postfixed in 1% OsO4 in 0.1 M cacodylate buffer at room temperature for 1 h, washed, dehydrated in a graded series of ethanol, and embedded in a mixture of Epon-Araldite (5). Thin sections were cut on a diamond knife, collected on 300-mesh copper grids, and examined in either a Philips 200 or 300 electron microscope, both unstained and after staining with uranyl acetate (25) and lead (21). Freeze-Fracture AnalysisAfter primary fixation for 20 min, cubes of tissue were washed thoroughly, equilibrated for 90 rain in 20% glycerol in 0.1 M cacodylate buffer, frozen on paper disks in liquid Freon 22, and stored in liquid nitrogen. A

Role of gap junction-mediated communications in regulating large-scale chromatin configuration remodeling and embryonic developmental competence acquisition in fully grown bovine oocyte

“…Intra-oocyte cAMP level is maintained by endogenous adenylate cyclases and constitutively active G-protein-coupled receptors [36]. cAMP is generated also by cumulus cells and then transported into the oocyte through gap junctions [37,38]. The manipulation of intracellular cAMP concentration has been demonstrated to influence functional coupling in bovine COCs [14,39].…”

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

“…Those that survive this process are ovulated and undergo the final phases of maturation that prepare the nucleus and cytoplasm for embryogenesis. 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.…”

Stops and starts in mammalian oocytes: recent advances in understanding the regulation of meiotic arrest and oocyte maturation

“…One long-standing hypothesis is that cAMP is produced by follicle cells and diffuses through gap junctions to the oocyte (Anderson & Albertini 1976, Bornslaeger & Schultz 1985, Piontkewitz & Dekel 1993, Webb et al 2002b. Gap junctions are present between the cumulus cells and the oocyte (Albertini & Anderson 1974, Anderson & Albertini 1976.…”