A Putative Splice Variant of Anti-Mullerian Hormone Receptor Missing the Transmembrane Domain in Hamsters and Mice.

Abstract

In female mammals, the size of the ovarian follicular pool decreases with age. However, in Siberian hamsters (Phodopus sungorus) the age-associated attrition of primordial follicles is modulated by day length. Short photoperiod profoundly inhibits hamster reproductive physiology and the number of ovarian primordial follicles was at least two-fold greater at 3, 6, and 12 months of age in females that were raised and maintained in short days as compared to hamsters that were held in long days. The levels of anti-Mullerian hormone (AMH) in the serum and ovary are also modulated by photoperiod in Siberian hamsters, and AMH was investigated because it has been found to inhibit primordial follicle activation in mice. To further elucidate the effects of AMH in reproductive activity and quiescence and its relationship with age, we examined expression of AMH receptor (Amhr2), a serine-threonine kinase membrane receptor. Early in the course of that investigation we found a putative Amhr2 mRNA splice variant lacking exon 4, which encodes the vast majority of the transmembrane domain. Ovarian RNA expression levels of both variants were measured in young and old animals. The level of the Amhr2 splice variant containing exon 4 was significantly higher in the ovaries from 12-month-old females than from 3-month-old hamsters, whereas levels of the splice variant lacking exon 4 were not statistically different in the two age groups. These data suggest age-specific differential regulation of these two RNA species in the ovary. In contrast to its receptor, the levels of ovarian Amh RNA trended in the opposite direction: lower in 12-month-old hamsters than in 3-month-old hamsters (P = 0.06). Hamster uterus and testis were also found to express the putative Amhr2 RNA splice variant, as was mouse ovary. The latter finding will facilitate a more thorough characterization of this splice variant, because the molecular tools for investigations in mice far exceed the availability for hamsters. (poster)