Focimatrix (focal intraepithelial matrix) is a novel type of basal lamina matrix arranged as aggregates between the granulosa cells.  Focimatrix is first observed when antral follicles enlarge to greater than 5 mm.  It increases in amount as follicles continue to enlarge and become steroidogenic, and it is then degraded at ovulation.  Previous studies of subpopulations of apical and basal granulosa cells¹ from antral follicles, and granulosa cells from preovulatory follicles² found that the levels of expression of steroidogenic enzymes correlated with expression of some focimatrix components, suggesting that they are co-ordinately regulated or that one induces the other.   It has also been hypothesised that focimatrix may disrupt the polarity of granulosa cells enabling the cells to luteinise into luteal cells.  To investigate if focimatrix is required for the luteinisation of granulosa cells, we cultured cells from pools of small (n=8, < 5mm) and large (n=7, > 10 mm) follicles for 4 days in DMEM/F12 medium containing 10% fetal calf serum, without or with 1 mM dibutyryl cAMP for induction of luteinisation.  Progesterone production was measured in the culture supernatant and mRNA levels for steroidogenic enzymes (CYP11A1, CYP19A1), focimatrix components (COL4A1, LAMB2), FSH receptor (FSHR) and LH receptor (LHCGR) were also measured.  Granulosa cells from small and large follicles cultured with dibutyryl cAMP showed characteristics of luteinisation, such as increased expression of CYP11A1 compared to fetal calf serum alone and before culture, as well as reduced expression of CYP19A1, FSHR and LHCGR.  Surprisingly, the expression of both focimatrix genes declined during culture independently of treatment.  Thus whilst focimatrix might play an important role during folliculogenesis and ovulation, it may not be necessary for the luteinisation of granulosa cells.

¹ Nguyen T et al., Mol Cell Endocrinol. 2012 Nov 5;363(1-2):62-73.

² Matti N et al., Mol Cell Endocrinol. 2010 Jun 10;321(2):207-14.