Breeding, Gonadal Development and Steroidogenesis in the Ovary of the Grey Short-Tailed Opossum, Monodelphis domestica

Maitland, Philip (1992) Breeding, Gonadal Development and Steroidogenesis in the Ovary of the Grey Short-Tailed Opossum, Monodelphis domestica. MSc(R) thesis, University of Glasgow.

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The Grey, short-tailed opossum, Monodelphis domestica, is a relatively recent acquisition to the laboratory. Possessing the desirable characteristics of all marsupials, such as quite early sexual maturity, few chromosomes and birth at an early developmental stage, as well as a short post partum dependence period and being more easily laboratory bred and tractable compared to other Didelphids, Monodelphis makes a good laboratory animal for developmental studies. This study takes advantage of the above facts, to add one more marsupial to the list of mammals in which physical development, gonadal development and the development of steroidogenesis in the ovary have been described. It was found that by introducing the female opossum to the male for mating, instead of vice versa, her natural aggression was curbed which, in turn, increased the numbers of successful pairings by 27% and cut neonatal losses due to cannibalism by 58%. The mating behaviour observed, average litter sizes attained of 7.5, the chronology of neonatal events and the calculation of a sex-ratio at weaning of 1:1 all confirmed previous studies by various authors. Monodelphis pups' head-length increased in direct proportion to their age, whereas their weight increased exponentially. It was also found that pups obtained before attachment to the nipple weighed around 20 mg less than their siblings which had, presumably, been fed. Large weight variations lead to the suggestion that head-length would make a better ageing criterion. The sexing of young by visual means proved impossible until day 3 (contrary to previous studies) and unreliable until day 8 when skin pigmentation, especially on the scrotum, is present. Gonads could be sexed at birth as the testis had already differentiated by then. Chromosomal analyses proved to be the best method of sexing pups, and confirmed the chromosome number of 2n = 18. Gonadal size sex differences were observed at birth. Testes, complete with testicular cords and a tunica albuginea, were consistently larger than ovaries of the same age. The ovary differentiated between days 5 and 6, no germ cell cords were formed and meiosis commenced around day 14. The ovarian blastema differentiated into stromal tissue and, between days 14 and 26, medullary cords. These cords, when they contacted oogonia, around day 29, provided the latter with their first follicle cells. Interstitial tissue was apparently formed from degenerated corpora lutea and possibly cells from atretic follicles and the stroma. The rete ovarii developed from a condensation of cells in the hilar region on day 5 and infiltrated the gonad. The rete abutted onto the medullary cords after follicle formation had begun and connections to mesonephric structures were not observed. Histochemical demonstration of the steroidogenic enzyme, 3beta-HSD, produced similar results to those found in most mammals. Immunocytochemical staining for the same enzyme produced different results to those found in the human. Combining the immunocytochemical and histological studies it was shown that Monodelphis ovaries are of the "immediate meiosis" type.

Item Type: Thesis (MSc(R))
Qualification Level: Masters
Additional Information: Adviser: Suzanne Ullmann
Keywords: Zoology, Endocrinology, Developmental biology
Date of Award: 1992
Depositing User: Enlighten Team
Unique ID: glathesis:1992-75194
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 21:48
Last Modified: 19 Nov 2019 21:48

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