DESTRUCTION OF THE GERMINAL DISC REGION OF AN IMMATURE PREOVULATORY CHICKEN FOLLICLE INDUCES ATRESIA AND APOPTOSIS

The germinal disc region (GDR), which contains the germinal disc and o verlying granulosa cells, is essential for completion of maturation of the preovulatory chicken follicle. The current study was conducted to test the hypothesis that destruction of the GDR (GDRX) of an immature preovulatory chicken follicle blocks ovulation, induces apoptosis, an d causes atresia. The GDR of immature preovulatory follicles (F2) were destroyed by freezing with dry ice (3 mm in diameter) 48-50 h before ovulation. As a control for the effect of freezing, a nonGDR portion ( a portion of the follicular wall opposite to the GDR relative to the f ollicular stalk) of other F2 follicles were destroyed (nonGDRX). Treat ment of F2 follicles by GDRX caused atresia and blocked ovulation of a ll treated follicles (6 of 6), whereas none of the nonGDRX follicles ( 0 of 5) underwent atresia. Treatment of follicles by GDRX induced apop totic DNA fragmentation (laddering) in theca and granulosa layers obta ined from the frozen area and in the theca layer obtained from the fol licular wall distal to the frozen area. In contrast, apoptosis was onl y present in theca and granulosa layers in the frozen area of the nonG DRX follicle. Furthermore, the in situ DNA end-labeling technique demo nstrated that in the GDRX follicle 24 h after treatment, cells in the theca interna, endothelial cells in blood vessels of the theca externa , and a few granulosa cells underwent apoptosis. These results indicat e that destruction of the GDR of an immature preovulatory follicle cau ses atresia and apoptosis and blocks ovulation. These novel findings s uggest that the GDR maintains development of the chicken preovulatory follicle by producing one or more survival factors. Without the CDR, c hicken follicles cannot develop further and they eventually die.