Masters Theses

Date of Award

8-1995

Degree Type

Thesis

Degree Name

Master of Science

Major

Life Sciences

Major Professor

Mary Ann Handel

Committee Members

Bruce D. McKee, Leslie G. Hickok

Abstract

Topoisomerases are nuclear enzymes functioning to remove torsional stress in DNA induced by replication, transcription, condensation, and recombination. Because of the potential importance of topoisomerases for various aspects of meiosis, I studied the expression of transcript and enzyme activity of topoisomerases I (topo I) and topoisomerase Ilα (topo II) during testicular development and spermatogenesis in the mouse. Analysis by Northern blots was made of total RNA extracted from testes of different developmental ages and of total RNA extracted from spermatogenic cell fractions enriched by sedimentation at unit gravity. Comparative quantitation of transcript level in different samples was made by densitometric analysis of autoradiograms. During development, topo I transcript was expressed at quite similar and increased levels in the testes from mice aged 8, 16, and 21 days, and decreased by day 30 and thereafter . The level of topo II transcript was highest in those testes where meiotic cells are abundantly represented (day 16 and 21). Interestingly, topo I transcripts were high in the testes of XXSxr (germ-cell deficient) mice, while levels of topo II were negligible in these testes, suggesting that most of the topo II activity in the whole testes derives from germ cells. From highly enriched cell populations, topo I transcript was high in type A and B spermatogonia, leptotene-zygotene spermatocytes, and pachytene spermatocytes, and then decreased dramatically in round spermatids. Enzyme activity, measured by a DNA relaxation assay, differed from transcript levels in also being high in round spermatids, thus suggesting enzyme stability. In the highly enriched spermatogenic cell populations, topo II transcript increased during spermatogenesis to high levels in pachytene spermatocytes and in round spermatids. These results demonstrate developmental regulation of both topo I and II and could imply meiotic function for these enzymes.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS