Doctoral Dissertations

Date of Award

5-1996

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Life Sciences

Major Professor

Mary Ann Handel

Committee Members

Jeffrey Becker, Ranjan Ganguly, Bruce McKee, Wesley Wicks

Abstract

The unique events of meiosis include the pairing and recombination of chromosomes during prophase of meiosis I; still little is known about these events in mammalian meiosis. In this study some of the basic mechanisms governing the structure and behavior of chromosomes, and the timing of events during male mammalian meiotic prophase are investigated in mouse spermatogenic cells. This has developed as three main areas of work; defining chromatin structure and function during prophase I, cell culture to establish a system for experimental analysis of meiosis, and cell cycle analysis.

During the pachytene stage of meiotic prophase in male mammals the X and Y chromosomes become transcriptionally inactive and establish a chromatin domain, the sex body, that is visually distinct from the transcriptionally active autosomes. We sought objective criteria to describe chromatin differences by assessing DNase-I sensitivity of sex chromosome and autosomal sequences. Results support the hypothesis that in pachytene spermatocytes the chromatin configuration of the X-Y pair in the sex body is more condensed and inaccessible to enzymatic digest, while the autosomal chromatin is in a more open configuration. We consider the possibility that this configuration may well be related to recombinational status.

This study also reports the use of a simple system for the short-term culture of pachytene spermatocytes, in which we have assayed parameters of cell function pertinent to meiotic prophase, namely chromosome pairing and synapsis. Little is known about the control of events ending the lengthy prophase of meiosis I and leading to the G2/M-phase transition in mammalian spermatocytes. We have utilized short-term cultures of pachytene spermatocytes to study events of the G2/M cell-cycle transition induced by the protein phosphatase inhibitor okadaic acid (OA). Treatment of cultured pachytene spermatocytes with OA induced a rapid and premature onset of events leading to the M phase. These results suggest that OA treatment overrides a cell-cycle checkpoint control that normally keeps pachytene spermatocytes in a lengthy prophase, and that this control may be exerted by regulation of protein phosphorylation status.

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