Ultrastructural changes in the ovaries of Sl/Slt mutant mice, showing developmental deficiency of follicles and tubular adenomas.

Structural changes in the ovaries of WBB6F1-Sl/Slt mutant mice aged 10, 25, 35, and 60 days and 7 months were studied light and electron microscopically. Neither secondary nor Graafian follicles could be found in any of the animals studied, and only primary follicles were usually seen until 35 days. In most follicles, the oocyte was lost. The hyperplastic proliferation of follicle epithelial cells, forming large round or oval cell clusters, occurred in 60-day-old mice. In 7-month-old animals, the ovaries were mostly occupied with invasive peritoneal epithelial tubules and masses of epitheloid cells which are apparently derived from the follicle epithelial cells. Although the ultrastructure of the oocyte and the follicle epithelial cell of the primary follicle is not different from that of +/+ control animals, the lack of gap junctions between the oocytes and the surrounding follicle epithelial cells may cause these abnormalities. The epitheloid cells that appeared in the 60-day-old animals are suggested to produce some steroid hormones, since they have cell organelles characteristic for steroid biosynthesis, such as well-developed smooth endoplasmic reticulum, oval mitochondria with tubulovesicular cristae, and numerous lipid droplets.