Granulosa cell expression of basal lamina matrices: Call-Exner bodies and focimatrix.

A Call-Exner body appears as a rosette of granulosa cells radially disposed (polarized) around an aggregate of extracellular matrix. The function of these bodies is unknown. A newly described matrix, focimatrix, also develops as aggregates of basal lamina-like material between granulosa cells. It appears much later in follicular development, and in a far greater amount than Call-Exner bodies. Its possible role is to reduce the polarity of epithelial granulosa cells allowing them to develop into non-polarized mesenchymal luteal cells upon ovulation of the follicle. Call-Exner bodies may arise from early and isolated expression of focimatrix.