In mammals, anti-Mü llerian hormone (AMH) is produced by Sertoli cells from the onset of testicular differentiation and by granulosa cells after birth. In birds, AMH starts to be expressed in indifferent gonads of both sexes at a similar level and is later upregulated in males. We previously demonstrated that, unlike in mammals, the onset of AMH expression occurs in chick embryo in the absence of SOX9. We looked for potential factors that might be involved in regulating AMH expression at different stages of chick gonad differentiation by comparing its expression pattern in embryos and young chicken with that of DMRT1, SF-1, WT1, GATA-4, Wnt-4, and

In rats, the pool of primordial follicles is established within the first 3 d postnatally (dpn). Immediately after their differentiation, a subset of follicles begins to grow and constitutes the initial follicular waves. In this study we investigated the development of these early growing follicles after deletion of the primordial follicle pool induced by 1.5 Gy gamma-irradiation at 5 dpn. Within only 24 h, i.e. at 6 dpn, 99% of the primordial follicles disappeared, whereas most of the growing follicles remained unaffected. The study of these surviving follicles throughout the immature period has shown that their subsequent growth proceeded normally, as assessed by proliferating cell nuclear antigen immunostaining and follicular counts. No modification in the process of follicular atresia, studied by terminal deoxynucleotidyltransferase-mediated deoxy-UTP-fluorescein nick end labeling and Southern blot of DNA fragmentation analysis, was observed. Complementary analysis, by either in situ hybridization for inhibin subunits, P450 aromatase, and LH receptor mRNAs or plasma dosages of 17beta-estradiol and inhibin B, further showed that follicular maturation was unaltered. In line with these observations, pubertal onset was normal, regarding both age and ovulation rate. Nevertheless, as a consequence of the nonrenewal of the growing pool, the follicular complement was practically exhausted at puberty, and 90% of the females evidenced sterility by 4 months. Altogether, our results demonstrate that the deletion of the primordial follicle pool has induced no modification in the growth pattern of the early growing follicles that develop as their counterparts in control ovaries. Within the immature period, the initial follicular waves ensure the ovarian functionality and thus play a key role in the initiation of reproductive life.

In mammals, the primordial follicle stock is not renewable, and its size, therefore, limits the reproductive life span of the female. In this study we have investigated the morphological and functional differentiation of dysgenesic ovaries in female rats exposed in utero to 1.5 Gy gamma-irradiation. As a consequence of the severe depletion in oocytes, females evidenced premature ovarian failure from 6 months on. Nevertheless, puberty onset and fertility at the beginning of reproductive life were similar to those of controls. The differentiation and evolution of the entire follicular population were followed during the immature period, using follicle counts, in situ hybridization of follicular maturation markers, and analysis of atresia. Primordial follicles were much more affected by irradiation (1.4-1.9% of controls) than growing follicles (30-45% of controls). As the very low number of primordial follicles remained constant throughout this period, it may be considered that the growing follicle pool plays the role of follicular reserve, permitting the transient normal fertility of irradiated females. Within the neonatal period, primary and secondary follicles, as revealed by proliferating cell nuclear antigen immunostaining, remain quiescent longer in irradiated than in control ovaries. Consequently, the majority of the most mature follicles (i.e. the first follicular wave) characterized by a high expression of aromatase transcripts during the infantile period, are missing in irradiated ovaries. Concomitantly, the 17beta-estradiol plasma peak is absent, and plasma FSH levels are higher than those in control females. In conclusion, these observations emphasize that the female reproductive life span depends not merely on the size of the primordial follicle stock, but also on the entire follicle complement as well as follicular dynamics during the immature period.