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Dissertation/Thesis Abstract

Analysis of DNA replication, sex chromosomes, and checkpoints in the Caenorhabditis elegans germ line
by Jaramillo-Lambert, Aimee, Ph.D., University of California, Davis, 2010, 119; 3427423
Abstract (Summary)

Meiosis is essential for all sexually reproducing organisms and consists of a single round of DNA replication followed by two rounds of nuclear division and specialized cell divisions that result in the production of two distinct haploid gametes, eggs and sperm. Meiotic DNA replication is important for the subsequent chromosomal interactions that occur during meiotic prophase which can differ extensively between sexes of the same species. Additionally, meiosis has surveillance mechanisms to monitor genome integrity as it passes to the next generation and the extent to which checkpoints monitor and safeguard the genome can differ between sexes. Taking advantage of the unique features of the Caenorhabditis elegans germ line, I investigated aspects of DNA replication, meiotic prophase progression, sex chromosomes and germ-line checkpoints. I found that meiotic S phase is at least twice as long as mitotic S phase in C. elegans germ cells and different regions of the genome replicate with different timing. I discovered that meiotic prophase for oogenesis lasts 54-60 hours while meiotic prophase for spermatogenesis is completed by 20-24 hours. Examination of meiotic progression in sex determination mutants revealed that meiotic prophase timing and germ-line apoptosis, one output of checkpoint signaling, is dictated by the sex of the germ line (oogenesis vs. spermatogenesis). Surprisingly, in feminized, fem-3lf X0 animals a single pair of asynapsed autosomes elicits a checkpoint response, but a single X chromosome fails to induce checkpoint activation. Further analysis revealed that the chromatin/transcriptional state of the single X chromosome locally precludes checkpoint signaling. Investigation into the molecular basis for the lack of checkpoint-activated apoptosis in the male germ line revealed that the 9-1-1 complex, ATR (ATL-1), and activated CHK-1 are recruited to unrepaired breaks in the male germ line. Further, CEP-1(p53) is expressed and induces expression of the pro-apoptotic protein EGL-1 in both hermaphrodite and male germ lines under checkpoint activating conditions. The core apoptotic machinery is expressed in both hermaphrodites and males, but caspase is activated in hermaphrodite but not male germ lines. Although apoptosis is not induced in male germ lines when there are errors in meiosis, checkpoint components improve the fidelity of chromosome inheritance.

Indexing (document details)
Advisor: Engebrecht, JoAnne
Commitee: Heyer, Wolf-Dietrich, Rose, Lesilee
School: University of California, Davis
Department: Genetics
School Location: United States -- California
Source: DAI-B 71/12, Dissertation Abstracts International
Subjects: Molecular biology, Genetics, Cellular biology
Keywords: Caenorhabditis elegans, Checkpoints, Chromatin modifications, Dna replication, Germ line, Meiosis, Sex chromosomes
Publication Number: 3427423
ISBN: 978-1-124-31624-6
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