A MORPHOMETRIC STUDY OF EARLY OVARIAN DEVELOPMENT IN POUCH YOUNG OF THE BRUSHTAIL POSSUM (TRICHOSURUS-VULPECULA)

Background: Although the pattern of gonadal differentiation in marsupi als is well documented, there is little information available on germ cell initiation and development. Furthermore, neither parameter has be en well described for the brushtail possum (Trichosurus vulpecula). Me thods: A quantitative study of ovarian germ cell proliferation and the onset of folliculogenesis was undertaken in pouch young of the brusht ail possum. Pouch-young age was estimated from measurements of head le ngth and crown-rump length. Estimates of total ovary volume, the numbe r of primary and meiotic germ cells, and the numbers of primordial fol licles were made by using Cavalieri's principle and the optical disect or. In addition, the age at which follicle growth began was determined . Results: The estimated ages of the pouch young in the study ranged f rom 26 to 207 days postpartum. Body weight, ovary weight, and ovary vo lume were all highly correlated with estimated age. Germ cell meiotic activity was well established by day (d) 26 of pouch life. Germ cell n umbers reached a maximum (691 x 10(3)/ovary) at d67 postpartum and the n declined with increasing age. Primordial follicles were first eviden t at d67, Primary follicles were first seen at d97, secondary follicle s at d105, and antral follicles at d155. Conclusions: This first quant itative study of ovarian follicle development in the female pouch youn g of the brushtail possum provides a basis for the temporal definition of ovarian maturation in this marsupial species. The pattern of germ cell proliferation and development is similar to that seen in eutharia n mammals. (C) 1996 Wiley-Liss, Inc.