Inverse expression of peroxisomes and connexin-43 in the granulosa cells of the quail follicle

Studying the regulation of peroxisome (Px) expression could improve our understanding of human peroxisomal disorders. The granulosa of the largest preovulatory quail follicles proved to be a relevant model because (a) Pr expression changes according to the follicular maturation stage and (b) Pr expression varies regionally according to the distance of the granulosa relative to the germinal disc region containing the female gamete (oocyte). The question was asked whether Pr expression is related to the extent of metabolic cell coupling and whether zonal Pr variation is causally related to oocytal factors. This was evaluated by the presence of catalase and Cx-43 (marker proteins for peroxisomes and gap junctions, respectively) and by in vitro experiments with granulosa explants. The data obtained show that the expression of Cx-43 and Pr is inversely correlated both temporally and spatially. Uncoupling of gap junctions results in an upregulation of alpha-catalase immunofluorescence. This is in agreement with reports that gap junctions are often negatively affected by Pr proliferators. The zonal gradient in Pr expression appears to be imposed by the oocyte, as is the case for steroidogenesis and proliferative capacity in the granulosa epithelium.