Date of Award

Spring 1985

Project Type

Dissertation

Program or Major

Zoology

Degree Name

Doctor of Philosophy

Abstract

Testes of Asterias vulgaris are potentially useful for investigating mechanisms regulating spermatogenic events because of their structural simplicity and annual spermatogenic cycle. Examination of major biochemical classes during the spermatogenic cycle provides a definition of the changing chemical microenvironment influencing germinal cells and also suggests temporal relationships among successive spermatogenic events. Testes from seastars collected throughout the year were homogenized and lyophilized and aliquots assayed for DNA, RNA, total protein, free amino acids, total lipids, glycogen, and other carbohydrates; spermatogenic stage was determined by examination of paraffin sections. The resulting data, expressed as (1) mg/g dry mass, (2) mg/mg DNA, and (3) total content, were analyzed by weighted periodic regression and circular-linear correlation with spermatogenic stage and time of year. The observed patterns of change correlate closely with cytological variations observed within the germinal epithelium. Biochemical data thus complement existing data on the cytology of the germinal epithelium.

Activity of ornithine decarboxylase (ODC), the rate-limiting enzyme of polyamine synthesis, increases during the proliferative phase of spermatogenesis. Testicular ODC activity correlates well with DNA synthetic rate. To test the possible role of polyamines in regulating initiation of spermatogonial mitoses, intact testes near the beginning of the proliferative phase were incubated in vitro with exogenous polyamines. They subsequently showed a significant increase in incorporation of ('3)H-thymidine into DNA. No statistically significant difference in thymidine incorporation could be detected among testes exposed to three incubation regimes: polyamines present on first day only, present second day only, and present both days; in all three cases, ('3)H-thymidine was added for the third day of incubation with the same type of medium as that used on the second day. Thus, the effect on DNA synthesis of extrinsic polyamines appears to be sustained after removal of the extrinsic polyamines. These results suggest a direct role for polyamines in the regulation of spermatogenic proliferation in A. vulgaris. Evidence for a regulatory role of polyamines in the initiation of proliferation, together with existing information on the environmental, hormonal, and cytological interactions, facilitates development of a preliminary model for regulation and entrainment of spermatogenesis.

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