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The soil-nematode Caenorhabditis elegans survives oxygen deprivation (anoxia < 0.001 kPa of O2, 0% O2) by entering into a state of suspended animation during which cell cycle progression at interphase, prophase and metaphase stage of mitosis is arrested. I conducted cell biological characterization of embryos exposed to various anoxia exposure times, to demonstrate the requirement and functional role of spindle checkpoint gene san-1 during brief anoxia exposure. I conducted a synthetic lethal screen, which has identified genetic interactions between san-1, other spindle checkpoint genes, and the kinetochore gene hcp-1. Furthermore, I investigated the genetic and cellular mechanisms involved in anoxia-induced prophase arrest, a hallmark of which includes chromosomes docked at the nuclear membrane. First, I conducted in vivo analysis of embryos carried inside the uterus of an adult and exposed to anoxic conditions. These studies demonstrated that anoxia exposure prevents nuclear envelope breakdown (NEBD) in prophase blastomeres. Second, I exposed C. elegans embryos to other conditions of mitotic stress such as microtubule depolymerizing agent nocodazole and mitochondrial inhibitor sodium azide. Results demonstrate that NEBD and chromosome docking are independent of microtubule function. Additionally, unlike anoxia, exposure to sodium azide causes chromosome docking in prophase blastomeres but severely affects embryonic viability. Finally, to identify the genetic mechanism(s) of anoxia-induced prophase arrest, I conducted extensive RNA interference (RNAi) screen of a subset of kinetochore and inner nuclear membrane genes. RNAi analysis has identified the novel role of 2 nucleoporins in anoxia-induced prophase arrest.

In this thesis I describe the construction of a cDNA library of maternal mRNA from the sea-urchin <i>Arbacia punctulata</i> and the subsequent isolation of a cDNA clone for the cylin protein using the technique of hybrid-arrest of translation. The cyclin protein was originally identified in sea-urchin embryos as a protein that was strongly synthesised after fertilisation but destroyed at each cell division (Evans <i>et al</i>, 1983). The DNA sequence of the putative cyclin clone was determined. It contains an open reading frame for a protein of M<SUB>r</SUB>46,000 which bears significant homology to the central region of the sequence of two other cyclin mRNAs found in eggs of the clam <i>Spissula solidissima</i>. The cyclin clone was subcloned into a T7 RNA polymerase transcription vector and the <i>in vitro</i> translation product of the encoded mRNA found to be a protein of apparent M<SUB>r</SUB>56,000 on a 1-D SDS acrylamide gel, which co-migrated with the <i>in vivo</i> synthesised cyclin protein. When the <i>in vitro</i> transcript was micro-injected into <i>Xenopus Aevis</i> oocytes it caused germinal vesicle breakdown, indicative of entry into meiosis, suggesting a role for cyclin in the control of the cell-cycle.

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