Doctoral Dissertations
Date of Award
8-2004
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Life Sciences
Major Professor
Bruce D. McKee
Committee Members
Mariano Labrador, Jae Park, Jeffrey Becker, Mary Ann Handel
Abstract
Our research interest is to uncover mechanisms underlying meiotic chromosome pairing and segregation. pairing failure 2 (pf-2) is a gene involved in this process during meiosis I of male Drosophila. The three pf-2 alleles recovered in a screen for chemically induced (EMS) mutations on chromosome III that cause paternal loss of chromosome IV display strong meiotic phenotypes. Cytological analysis of testes of pf-2 mutant flies revealed unpaired chromosomes at prophase and metaphase I and “laggard chromosomes” at anaphase I in primary spermatocytes. Meiosis II appears relatively normal. Genetic data confirm that non-disjunction occurs at the first meiotic division and affects the segregation of sex chromosomes as well as autosomes. By deficiency complementation pf-2 was mapped to region 93D6; 93E1 on chromosome arm 3R and shown to be allelic to modifier of mdg4 [mod(mdg4)], a complex locus that encodes a large family of chromosomal proteins by alternative and trans-splicing. The encoded proteins together occupy more than 500 sites on the polytene chromosomes. We show that the pf-2 mutations disrupt the function of a single isoform, Mod(mdg4)56.3, that is expressed in primary spermatocytes at all stages. Both a GFP-tagged Mod(mdg4)56.3 transgene and the native Mod(mdg4)56.3 protein localize as discrete foci to the major autosomes, and as an intensely fluorescent cluster of foci to the nucleolus throughout prophase. The nucleolar cluster resolves into a sharply defined structure associate with the X-Y bivalent. We conclude that Mod(mdg4)56.3 plays a critical role in homologous chromosome pairing in Drosophila male meiosis. Transgenic flies with a pf-2 null genetic background and carrying [hsp70-pf2 cDNA] fragment on their chromosome II display a complete rescue of the pairing failure phenotype. The expression pattern of the GFP-labeled Mod(mdg4)56.3 in transgenic flies’ meiotic cells implies a role for this novel gene in chromosomal cohesion during meiosis.
Recommended Citation
Bejnood, Morvarid Soltani, "modifier of mdg4 encodes a protein involved in homologous chromosome pairing in Drosophila melanogaster males. " PhD diss., University of Tennessee, 2004.
https://trace.tennessee.edu/utk_graddiss/4526