Johnson A L, Bridgham J T, Digby M R, Lowenthal J W
Department of Biological Sciences, The University of Notre Dame, Indiana 46556, USA.
Biol Reprod. 1998 Feb;58(2):414-20. doi: 10.1095/biolreprod58.2.414.
It is now well established that within the hen ovary, preovulatory follicles rarely become atretic and that granulosa cells from preovulatory follicles are relatively resistant to undergoing apoptosis in vitro. By comparison, prehierarchal (< or = 8-mm diameter) follicles are highly susceptible to becoming atretic in vivo, and approximately 70% of granulosa cells collected from 3- to 8-mm-diameter follicles rapidly undergo apoptosis when incubated for as little as 6 h in vitro in defined medium. The present studies were conducted to characterize expression of an inhibitor of apoptosis (iap) gene, inhibitor of T-cell apoptosis (ita), within hen follicle tissues at various stages of follicle development. The ita gene product has recently been shown to share homology within both the baculovirus repeat sequences of the N-terminus and the zinc ring-finger motif from the C-terminus and was originally determined to be expressed in chicken cells of T-lymphocyte lineage. In the present studies, highest levels of ita mRNA within the granulosa cell layer were found in preovulatory (atresia-resistant) follicles, with significantly lower levels detected in prehierarchal follicles. After 24 h of primary culture, ita mRNA levels increased in granulosa cells from preovulatory follicles by 3.2-fold as compared to those in freshly collected cells and were elevated by 8.9-fold in those granulosa cells from 6- to 8-mm follicles that successfully formed a primary culture monolayer. Moreover, ita mRNA levels were significantly increased in 6- to 8-mm-follicle granulosa cells after only 2 h of suspension culture, and this increase could be prevented by actinomycin D. This spontaneous increase in ita expression may serve to protect from cell death the relatively small population of prehierarchal follicle granulosa cells that survive in vitro. It is concluded from these data, taken together, that patterns of ita mRNA expression during follicle development are consistent with a potential role for this gene in protecting granulosa cells from apoptosis and thus maintaining follicle viability.
现已充分证实，在母鸡卵巢内，排卵前卵泡很少发生闭锁，且排卵前卵泡的颗粒细胞在体外相对不易发生凋亡。相比之下，等级前（直径≤8毫米）卵泡在体内极易发生闭锁，从直径3至8毫米卵泡收集的颗粒细胞，在限定培养基中体外培养仅6小时，约70%会迅速发生凋亡。本研究旨在表征凋亡抑制因子（iap）基因——T细胞凋亡抑制因子（ita）在母鸡卵泡发育不同阶段的卵泡组织中的表达情况。ita基因产物最近显示，其在N端的杆状病毒重复序列和C端的锌环指基序中均具有同源性，最初被确定在T淋巴细胞谱系的鸡细胞中表达。在本研究中，颗粒细胞层中ita mRNA的最高水平见于排卵前（抗闭锁）卵泡，在等级前卵泡中检测到的水平显著较低。原代培养24小时后，排卵前卵泡颗粒细胞中的ita mRNA水平比新鲜收集的细胞增加了3.2倍，在成功形成原代培养单层的6至8毫米卵泡的颗粒细胞中升高了8.9倍。此外，悬浮培养仅2小时后，6至8毫米卵泡颗粒细胞中的ita mRNA水平就显著增加，且这种增加可被放线菌素D阻止。ita表达的这种自发增加可能有助于保护体外存活的相对少量的等级前卵泡颗粒细胞免于细胞死亡。综合这些数据得出结论，卵泡发育过程中ita mRNA的表达模式与该基因在保护颗粒细胞免于凋亡从而维持卵泡活力方面的潜在作用一致。
