Faculty and Research Interests

Gary R. Marshall
Ph.D., University of Texas Health Science center at Houston
Hormonal Regulation and Cell Biology of Primate Spermatogenesis

Dr. Marshall's continues to study the regulation and cell biology of testicular function in non-human primates. At the time of puberty, Sertoli cells, the somatic cells of the seminiferous epithelium, undergo a six-fold increase in number that is driven by gonadotropin secretion. Recently, his laboratory has shown that Sertoli cell proliferation in primates, in contrast to that in rats, may stimulated by either LH or FSH. Moreover, neither LH nor FSH were able to initiate spermatogenesis, but the combination of both gonadotropins did stimulate the first steps of the initiation of the process. Experiments are beginning to investigate the cell biology and paracrinology of LH action to stimulate Sertoli cell proliferation as well as the hormonal regulation of the initiation of spermatogenesis. In the adult primate testis, FSH has the specific role of amplifying the population of differentiated spermatogonia. Experiments have been done and the tissues are being analyzed to determine whether this amplification is due to a reduction in programmed cell death, apoptosis and whether the rescue of these germ cells is limited specifically to one phase of the cell cycle. A variety of physiological, histochemical and molecular techniques are being used. These include, quantitative in situ hybridization histochemistry, immunocytochemistry, quantitative stereological analysis of cell number, BrDU labelling, and physiological, pulsatile iv replacement treatments of recombinant cynomolgus LH and FSH to monkeys maintained in remote sampling/infusion cages. Dr. Marshall studies of the gonadotropin and paracrine regulation of spermatogenesis are conducted in collaboration with Dr. Plant. The goal here is to gain an integrative understanding of the hypothalamic-pituitary-testicular control system governing spermatogenesis in a representative higher primate. Dr. Marshall also works closely with Dr. Walker and Onate, and as Dr. Marshall studies on FSH dependent spermatogonial proliferation proceeds to the cellular and molecular levels these interactions will become more significant.

Representative Publications

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