No abstract

The first critical transition in follicular development, the activation of primordial follicles to leave the pool of resting follicles and begin growth, is poorly understood, but it appears that the balance between inhibitory and stimulatory factors is important in regulating the exodus of follicles from the resting pool. There is evidence that anti-Mullerian hormone (AMH; also known as MIS) inhibits follicle activation in mice, but whether it plays a similar role in non rodent species is not known. When pieces of bovine ovarian cortex, rich in primordial follicles, are cultured in serum-free medium, most follicles initiate growth, but when cortical pieces are grafted beneath the chorioallantoic membrane (CAM) of chick embryos, follicle activation does not occur. Since embryonic chick gonads of both sexes produce and secrete high levels of AMH, the hypothesis that the AMH in the chick circulation inhibits follicle activation was tested. In Experiment 1, whole newborn mouse ovaries were grafted beneath the CAM (placed "in ovo") or cultured in vitro for 8 days. In vitro (or after 8 days in vivo) follicles activated and proceeded to the primary or secondary stage, but activation was suppressed in ovo. This inhibition was reversed if ovaries were removed from beneath the CAM and cultured in vitro. In contrast, when ovaries from mice null mutant for the AMH type II receptor were CAM-grafted in Experiment 2, follicle activation occurred in a similar fashion to activation in vitro. This finding strongly implicates AMH as the inhibitor of follicle activation in ovo. Since chick embryonic gonads are the source of circulating AMH, chicks were gonadectomized in Experiment 3, prior to grafting of pieces of bovine ovarian cortex beneath their CAMs. Bovine primordial follicles activated in the gonadectomized chicks, similar to the results for mice lacking the AMH type II receptor. Taken together these experiments provide strong evidence that AMH is the inhibitor of mouse follicle activation present in the circulation of embryonic chicks and provide indirect, and hence more tentative, evidence for AMH as an inhibitor of bovine follicle activation.

The CAM graft will provide a useful model for studying the factors involved in activation of primordial follicles.

Age-0 yellow perch, Perca flavescens, shift from pelagic to demersal waters of Oneida Lake, New York, between late June to mid-July, when they reach standard lengths of 24–31 mm. The timing of this habitat shift coincides with the size range over which yellow perch achieve a degree of visual resolution that nearly equals that of adult yellow perch, from 174 min of arc in newly hatched larvae to 9–12 min in adults. This visual improvement is reflected in the yellow perch's diet, which consists of an increasingly wider range of prey sizes and types. If twin cones are counted as functionally separate photoreceptors, there is a significant improvement of the calculated visual acuity in larval fish with lenses < 1 mm in diameter but not in older fish with larger lenses. During its rapid growth phase the most optimistic calculation of visual acuity in a young yellow perch is insufficient to explain the feeding success necessary at this time. We suggest therefore that young yellow perch spend more time in search of prey than their adult counterparts.