(MS19) Extracellular matrix and the maturation of follicular cells.

Abstract

Extracellular matrix is diverse in composition and cells rarely alter their behaviour without reference to the composition and structure of the matrix. Thus it is not surprising that when follicles commence growing the follicular basal lamina underlying the membrana granulosa changes in its composition. Initially all six a chains of type IV collagen are expressed whilst during growth only 1 and 2 are. Perlecan and nidogen 1 subsequently become components of the follicular basal lamina, and there is an increase in the amount of laminin chains 1, 2, and 1 at least in the bovine. These changes accompany the activation of follicles and division and replication of granulosa cells. Other matrix components exist and also change during follicular development. A novel extracellular matrix (which we call fociemix for focal intra-epithelial matrix) is composed of basal lamina-like material and deposited as plaques or aggregates between the granulosa cells. Fociemix contains the same components as the follicular basal lamina at the corresponding stage of follicular development. The amount of fociemix increases with increasing follicle size, its appearance preceding granulosa cells expression of the steroidogenic enzymes in the days prior to ovulation. We propose that fociemix disrupts granulosa cells polarity induced by the follicular basal lamina prior to ovulation. Hence fociemix may have a key role in the follicular/luteal epithelial mesenchymal transition. Versican, inter-a-trypsin inhibitor, TSG-6 and hyaluronan have a key role in cumulus oocyte expansion and fertility. Versican is likely to have other significant roles in follicular development, based upon its pattern and timing of expression.