PARENT SESSION
SLIDE SESSION 2: FACTORS REGULATING EARLY FOLLICULAR DEVELOPMENT
Chairs: Evelyn Telfer, Robert Koos, Leanne Sleer (Trainee)
Univ Ottawa-UCU Auditorium
2:30 PM-4:30 PM
11
ACTIVATION OF MOUSE PRIMORDIAL FOLLICLES IS INHIBITED IN CHORIOALLANTOIC MEMBRANE GRAFTS.
Cushman, R1, Gigli, I1, Wahl, C2, Fortune, J1, 1 2
ABSTRACT- The mechanisms controlling primordial follicle activation are poorly understood. Most primordial follicles in pieces of bovine ovarian cortex activate and begin to grow in vitro. In contrast, when bovine cortical pieces are grafted beneath the chick chorioallantoic membrane (CAM, in ovo), activation does not occur, suggesting the presence of an inhibitor of activation in ovo. The inhibition is reversed when CAM grafts are transferred to organ culture. To test the hypothesis that the inhibition would also be exerted on primordial follicles in whole ovaries, ovaries were obtained from C57BL/6J mice on the day of birth (Day 0), when the ovaries have only primordial follicles, and grafted beneath the CAM of 6-day-old chick embryos for 8 days. Controls included ovaries fixed: 1) on Day 0, 2) after 8 days in vivo, and 3) after 8 days in vitro. Ovaries were embedded in plastic and serially sectioned for morphometric analysis (n = 4 mice/group). On Day 0, ovaries contained only primordial follicles, whereas after 8 days in vivo or in vitro, primary and secondary follicles had developed, as expected (Eppig and O'Brien, BOR 54:197, 1996). Interestingly, ovaries had more growing (primary + secondary) follicles after 8 days in vitro compared to Day 8 in vivo (12 ± 2.3 vs. 7 ± 2.6/section; P < 0.01). Although the total number of follicles did not differ between these two groups, the percentage of growing follicles was greater on Day 8 in vitro vs. in vivo (50 ± 4 vs. 30 ± 9%; P < 0.01). Ovaries maintained in ovo became vascularized and had only a very small number and percentage of growing follicles (0.4 ± 0.2/section and 3 ± 1%; P < 0.01 vs. Day 8 in vitro or in vivo). In all groups, >90% of follicles were healthy, and follicle and oocyte diameters increased with stage and day (P < 0.01), but did not differ among groups. These data suggest that in mouse ovaries the rate of activation is increased in vitro compared to in vivo, possibly due to lower concentrations in vitro of a negative regulator of follicle activation. In addition, the results support the hypothesis that chick embryos also produce an inhibitor of activation. Since both developing mammalian follicles and embryonic chick gonads secrete anti-mullerian hormone, it is a candidate for the putative inhibitor. Supported by the USDA (#00-35203-9151), NIH (F32 HD-08624), and University of Buenos Aires (I.G.).
KEY WORDS: oocyte, follicular development, follicle culture, gonadal development