EXPRESSION OF BCL-2 AND NR-13 IN HEN OVARIAN FOLLICLES DURING DEVELOPMENT

Follicle atresia is initiated within the granulosa cell layer of ovari an follicles and is mediated via the process of apoptosis. In the hen, at least two populations of granulosa cells can be distinguished duri ng follicle development on the basis of their inherent susceptibility or resistance to apoptosis, in vitro. Given the previously established correlation between expression of bcl-x(Long) and hen granulosa cell resistance to apoptosis, the present studies were conducted to charact erize expression of bcl-2 and an avian bcl-2 homologue, nr-13, in foll icles at various stages of development. Levels of nr-13 mRNA were sign ificantly higher only in granulosa cells from the largest (F1) preovul atory follicle compared to 3- to 5-mm prehierarchal follicles. By comp arison, bcl-2 mRNA levels were 5- to 9-fold higher in granulosa cells from the three largest preovulatory follicles compared to those from f ollicles 9 to 12 mm in diameter and prehierarchal follicles. The incre ase in neither nr-13 nor bcl-2 was correlated with the stage of follic le development associated with the acquisition of resistance to apopto sis in granulosa cells (e.g., at the 9- to 12-mm stage). Results from the present studies do not support a close correlation between constit utive expression of nr-13 or bcl-2 mRNA and the transition from a stat e of apoptosis susceptibility to apoptosis resistance in hen granulosa cells. Thus, it is proposed that nr-13 and bcl-2 play more of a suppo rtive role in regulating additional aspects of ovarian cell function s uch as cell proliferation and/or differentiation.