Endocrine Abstracts

Initial follicle growth results in a number of distinct morphological changes, such as cuboidalisation and proliferation of the granulosa cells (GC) as well as an increase in oocyte size.

Cell adhesion molecules and intercellular junctions play a pivotal role in changes in cell shape. We hypothesize that change in GC shape is key, and that increased understanding of changes in cell adhesion and associated junctions will provide insight into the regulation of initiation of follicle growth and help identify key regulators, and their mechanisms of action.

Follicles were isolated from day 12 and 21 mouse ovaries for mRNA analysis of proteins associated with cell adhesion. RT-PCR was used to screen for cell adhesion and junctional proteins in isolated follicles of similar sizes. Isolated oocytes, pure GCs and immortalized mouse GCs (KK1 cells) were also included in the PCR screen.

Molecules involved in cell adhesion including afadin, nectin and ZO-1 were detected in growing follicles.

Interestingly, E-cadherin mRNA was not detected in any GC samples, however was detected in both oocyte and follicle samples. Immunohistochemistry for E-cadherin confirmed protein expression was restricted to the oocyte membrane at all stages of follicle development.

Oocytectomised follicles confirmed that removal of the oocyte was associated with ablation of E-cadherin expression. Further analysis using immunohistochemistry and RT-PCR suggested that N-cadherin is alternatively involved in adhesion between GCs, associated with the linker protein β-catenin.

Since E-cadherin is normally associated with adherens junctions between epithelial cells, these results suggest GCs are not truly epithelial, and that E-cadherin may have a unique role in oocyte/GC interaction.

We can now assess the role of the oocyte in paracrine regulation of GC adhesion during early follicle development.