Figure 5. Oocyte cyst breakdown is disrupted in the Gas2 null mutant mice.

At P7.5, the processes of oocyte cyst breakdown and primordial follicle assembly are completed in wild type mice, and the ovarian cortex contains mostly oocytes surrounded by pre-granulosa cells and other somatic cells instead of clusters of oocytes (A) (H&E staining). In comparison, large regions of compacted oocyte clusters persist in ovaries of Gas2 null mice (B) (H&E staining), indicating disrupted breakdown of oocyte cysts. Dotted lines in the H&E images outline regions of compacted oocyte clusters. The difference in oocyte cyst breakdown was further illustrated by immunofluorescent labeling of oocytes with anti-STAT3 antibody (red) and nuclei counter staining by DAPI (blue). Oocytes in wild type mice are mostly separated from each other by somatic cells (A), but many of them remained immediately next to each other in Gas2 null mice (B). This disrupted breakdown of oocyte cysts in Gas2 null mice was apparent as early as P1.5 as shown by STAT3 staining in comparison to wild type mice (C,D).