title: Continuous loss of oocytes throughout meiotic prophase in the normal mouse ovary.
abstract: The number of germ cells reaches the maximum just prior to entry into meiosis, yet decreases dramatically by a few days after birth in the female mouse, rat, and human. Previous studies have reported a major loss at the pachytene stage of meiotic prophase during fetal development, leading to the hypothesis that chromosomal pairing abnormalities may be a signal for oocyte death. However, the identification as well as the quantification of germ cells in these studies have been questioned. A recent study using Mouse Vasa Homologue (MVH) as a germ cell marker reached a contradictory conclusion claiming that oocyte loss occurs in the mouse only after birth. In the present study, we established a new method to quantify murine germ cells by using Germ Cell Nuclear Antigen-1 (GCNA-1) as a germ cell marker. Comparison of GCNA-1 and MVH immunolabeling revealed that the two markers identify the same population of germ cells. However, nuclear labeling of GCNA-1 was better suited for counting germ cells in histological sections as well as for double labeling with the antibody against synaptonemal complex (SC) proteins in chromosome spreading preparations. The latter experiment demonstrated that the majority of GCNA-1-labeled cells entered and progressed through meiotic prophase during fetal development. The number of GCNA-1-positive cells in the ovary was estimated by counting the labeled cells retained in chromosome spreading preparations and also in histological sections by using the ratio estimation method. Both methods demonstrated a continuous decline in the number of GCNA-1-labeled cells during fetal development when the oocytes progress through meiotic prophase. These observations suggest that multiple causes are responsible for oocyte elimination.
authors.affiliation: Department of Biology, McGill University, H3A 1B1, Montreal, Quebec, Canada.
authors.forename: Kelly A
authors.initials: KA
authors.lastname: McClellan
authors.forename: Roger
authors.initials: R
authors.lastname: Gosden
authors.forename: Teruko
authors.initials: T
authors.lastname: Taketo
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D034961:Antigens, Nuclear / Q000378:metabolism; D015415:Biomarkers; D002452:Cell Count; D016923:Cell Death; D023902:Chromosome Pairing; D004268:DNA-Binding Proteins / Q000378:metabolism; D005260:Female; D005865:Gestational Age; D007150:Immunohistochemistry; D008540:Meiosis; D051379:Mice; D057136:Nuclear Receptor Subfamily 6, Group A, Member 1; D009865:Oocytes / Q000166:cytology* / Q000378:metabolism; D010053:Ovary / Q000166:cytology* / Q000196:embryology* / Q000254:growth & development / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid
chemical_list: D034961:Antigens, Nuclear; D015415:Biomarkers; D004268:DNA-Binding Proteins; C539950:NR6A1 protein, human; C539954:Nr6a1 protein, mouse; C539956:Nr6a1 protein, rat; D057136:Nuclear Receptor Subfamily 6, Group A, Member 1; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid