Patterns of RNA synthesis in early meiotic prophase oocytes from fetal mouse ovaries

In a study of the early meiotic prophase stages of mouse oogenesis from d12 of gestation to 10d post-partum the patterns of RNA synthesis during these stages of oogenesis using H³-uridine incorporation as visualized by light microscope autoradiography are reported. We find that chromosomal RNA synthesis occurs in all stages except early to mid-pachytene, the time of maximum chromosome condensation. Diplotene and dictyate nuclei are the most heavily labelled stages. Nucleolar labelling ceases before leptotene and reappears in late pachytene or early diplotene, even though nucleoli can be identified in all stages except early to mid-pachytene.