Patterns of Cellular Peptide Synthesis by Cultured Bovine Granulosa Cells*

Abstract

The electrophoretic distribution of the polypeptides synthesized by bovine granulosa cell cultures after metabolic labeling with [35S]methionine has been analyzed by double gel electrophoresis. The fluctuations of 35 polypeptides have been followed as a function of the size of the follicles from which cultures originated, as a function of the cultures' proliferative stage (sparce, actively growing vs. confluent, resting cultures), and finally as a function of whether cells were exposed to either epidermal or fibroblast growth factor. When the patterns of protein synthesis in sparce vs. confluent granulosa cell cultures derived from small-sized follicles were compared, only a few differences were observed. In confluent cultures, 6 new peptides appeared, while 1 peptide present in sparce cultures disappeared. Cultures maintained in the presence of fibroblast or epidermal growth factor synthesized 20 new peptides upon reaching confluence. Among these were the 6 new peptides present in confluent but not in sparse granulosa cell cultures maintained in the absence of growth factors. The changes in protein synthesis observed in cultures grown in the presence of growth factors may reflect their direct effect on the cellular metabolism. A comparison between the protein distribution in cells derived from small- vs. large-sized follicles showed that fewer proteins were ultimately produced at confluence in cells derived from large-size follicles than in cells derived from small-sized follicles. This could be related to the process of cellular differentiation taking place within granulosa cells. The patterns of [35S]methionine-labeled proteins secreted by the granulosa cells into the incubation medium were analyzed and found to be similar regardless of the size of the follicle from which the culture originated. Little similarity between the proteins present in the follicular fluid and the pattern of the labeled proteins secreted into the incubation medium by cultured granulosa cells was observed. Only three proteins were identified which comigrate with proteins present in the follicular fluid. One of these was identified as fibronectin. This raises the possibility that the fibronectin present in the follicular fluid originated from granulosa cells and is not derived from plasma.

Insulin-like growth factor-I stimulates oxytocin and progesterone production by bovine granulosa cells in culture

“…It can also increase DNA and protein synthesis in bovine granulosa cells (Franchimont, Hazee-Hagelstein, Charlet-Renard & Jaspar, 1986). In contrast to the present results, an inhibitory effect of EGF on secretion of progesterone by bovine granulosa cells has been observed (Savion & Gospodarowicz, 1980;Franchimont et al 1986). The inhibition by EGF was dose-dependent after 72 h of incubation (Franchimont et al 1986).…”

“…The stimulatory effect of EGF on the production of oxytocin and progesterone in the present study is therefore surprising. One explanation for the differ¬ ences observed could be the incubation time of 120 h in our experiments, or the supplementation of the medium with 10% fetal calf serum in the studies of Savion & Gospodarowicz (1980) and Franchimont et al (1986).…”

In Vitro Production of Estradiol by Bovine Granulosa Cells: Evaluation of Culture Condition, Stage of Follicular Development, and Location of Cells Within Follicles1

“…Whether the differences between studies are due to the source or level of attachment factor or other factors remains to be determined. As granulosa cells secrete fibronectin [44], endogenous production of fibronectin may also influence the results of studies in which the effects of supplemental attachment factors are evaluated.…”

Secretion of fibronectin by rat granulosa cells occurs primarily during early follicular development

“…However, there was also a considerable amount of this glycoprotein released into the medium as a soluble product. Fibronectin has been shown to be a component of bovine follicular fluid (Savion & Gospodarowicz, 1980). Indeed, granulosa cells were proposed to be a source of this fibronectin due to the existence of a blood-follicle barrier to substances having molecular weights greater than 1-5 105 (Shalgi et ai, 1973) thereby preventing the diffusion of plasma-derived fibronectin (Mr2-2 x 105) into this fluid compartment.…”

“…Fibronectin has been shown to be secreted by rat (Skinner & Dorrington, 1984) and bovine (Savion & Gospodarowicz, 1980) granulosa cells during culture. Indeed, by Day 3, this adhesive glycoprotein can represent 20% of the total radiolabelled proteins secreted by granulosa cells iso¬ lated from preantral ovarian follicles (Skinner & Dorrington, 1984).…”