| Summary: | 碩士 === 國立清華大學 === 生命科學系 === 91 === Gene duplication has been regarded as the most important mechanism for genetic novelties, biological divergence and complexity. Gene duplication is also suggested involving in speciation, however, there is no empirical studies showing the correlation between known speciation genes and duplication. Duplication of Odysseus (OdsH) and unc-4 in Drosophila possibly provide a bridge between the two. OdsH is the first defined hybrid male sterility gene between D. mauritiana and D. simulans, and it was recently duplicated from unc-4. Previous studies showed that in D. melanogaster, unc-4 is highly expressed in developing neurons, testes, and ovaries, and OdsH is mainly expressed in adult male testes, suggesting the two genes have undergone functional divergence. In this study, we further investigated the long-term evolution of unc-4 homologs and compared sequences and expression of OdsH and unc-4 in diverged species of Drosophila. Our results showed that there are two unc-4 homologs in D. pseudoobscura but only one in Anopheles gambiae, indicating the duplication was occurred before the divergence of D. pseudoobscura and D. melanogaster subgroup. Based on the nucleotide substitution, we showed that OdsH and unc-4 were duplicated about 47 Myr ago. unc-4 is conserved both in sequences and expression in Drosophila, while OdsH is very diverged. In D. pseudoobscura, OdsH is also expressed in embryo, similar to the pattern of unc-4, where as OdsH lost the expression in embryo, and switched to high expression in adult male testes in D. melanogaster. Evolutionary analysis also showed that OdsH is merely rapidly evolved within the D. melanogaster subgroup, possibly correlating to the expression switch and involving in new functions. The rapidly evolved OdsH gene duplicated from the conserved unc-4 is the first evidence for the relationship between gene duplication and speciation.
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