Reproduction Abstracts

The oocyte influences hormonal and cellular changes in the follicle and the ovary. Theca cells, surrounding the follicle basement membrane, synthesise androgen and thus regulate ovarian oestrogen production. The vascular theca layer provides nutrients to the avascular inner follicle. In C1galt1 mutant mice, all oocytes lack core 1-derived O-glycans due to oocyte-specific ablation of core 1 beta 1,3-galactosyltransferase. C1galt1 mutants have increased fertility resulting from modified follicle development and thus endocrinology. Since testosterone levels were decreased in the mutant, we investigated if the quantity of theca cells was modified during follicle development. Ovaries were collected at the four stages of the estrus cycle and subsequently fixed, paraffin embedded, and sectioned. Hyaluronic acid binding protein, which localised to theca cells, was detected using immunohistochemistry. Follicle development was assessed measuring the area and depth of theca cells, and the intensity of hyaluronic acid detected, using ImageJ. Theca area, depth, and hyaluronan levels were decreased in mutant primary (stages 3a and 3b) and secondary (stage 4) follicles compared to controls at metestrus, whereas at diestrus only theca depth was decreased. Mutant preantral follicles (stages 5a and 5b) also exhibited a decrease in theca area and depth and thus follicle area compared to control at metestrus. Theca cells of mutant antral follicles (stages 5a+A and 5b+A) contained less hyaluronan compared to control follicles at metestrus. Large antral mutant follicles had a reduced theca area at metestrus compared to controls but increased hyaluronan levels at proestrus. Overall, mutant follicles have less theca and hyaluronan in theca extracellular matrix, most evident at the metestrus stage. These results highlight the role of the oocyte in regulating both the amount of theca cells and extracellular matrix. They also demonstrate the rapid and dynamic changes that occur throughout the estrus cycle, with theca cell structure changing on a daily basis.