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Abstract
The CDK-cyclin complex is the major regulator of cell cycle. Multiple
mechanisms control the CDK-cyclin complex activity, among them there are two
important mechanisms: the activating phosphorylation of CDKs by CDK-activating
kinases (CAKs) and proteolysis of CDK regulators through the ubiquitination-26s
proteasome pathway. This dissertation consists of two projects. In the first study,
genome-wide phylogenomic analysis were performed to study the evolutionary
relationship of the CDK extended family in Saccharomyces cerevisiae,
Schizosaccharomyces pombe, Arabidopsis, C. elegans, Drosophila, and humans. The 4x
sequenced Giardia lamblia genome was also scanned by BLAST, PROFILE, and HMM
in search for ortholog of one of the CDK gene, the CAK Cak1. We were able to assign
orthology to the majority of the CDK genes, and our results allowed us to make the
following new observations: 1) CDK-related genes from Saccharomyces cerevisiae,
Schizosaccharomyces pombe, C. elegans, Drosophila, and humans can be put into ten
clades. Among them, seven clades appear to be ancestral, because they contain both
yeast and metazoan orthologs. 2) 13 of the Arabidopsis CDKs form an exclusive clade
with no ortholog from any other organism, suggesting a gene divergence event happening only in plants. 3) The divergent CDK family member, Cak1, has orthologs only in yeasts but not in any other organisms, suggesting that the Cak1 clade is highly divergent and might have not been conserved in eukaryotes. 4) In metazoa, there are divergent CDKs whose orthology could not be assigned. These divergent metazoan CDKs could serve as candidates for functional analysis in search of unidentified metazoan CAK(s).
In the second study, insights into meiotic cell cycle control as well as anteriorposterior polarity in C. elegans were gained by studying animals that are depleted of the CUL-2 cullin/RING finger ubiquitin ligase complex, which has been shown to regulate protein degradation. We found that in cul-2 mutant, the anaphase II chromosomes movement is severely delayed or abolished, and the early embryo polarity cannot be established correctly. Our result showed that the CUL-2 cullin ring-finger complex is required for anaphase II-specific chromosome movement but not for chromosome separation. This study provides the first evidence that cullin/RING finger complexdependent protein degradation is needed to regulate meiotic anaphase and polarity.