| Research Abstract |
Horizontal or lateral gene transfers between distantly separated species are common in bacteria. In eukaryotes, however, horizontal gene transfers have not been reported with a few exceptions : Mita et al. (2003) reported that several genes found in the Born byx EST database that encode a chitinase (BmChi-h), sucrase (beta-fructofuranosidase), glycerophosphoryl phosphodiesterase (GlpQ), and glucose-l-phosphatase, show higher homology to bacteria than to eukaryotes. Among these, BmChi-h has been mapped to the silkworm chromosome (Daimon et al., 2003). These are candidates for horizontal gene transfer between lepidopterans and bacteria. The enzymatic properties of BmChi-h were further analyzed in this study.
Not only are there bacterium-derived genes, but also baculovirus-derived genes in the Born byx and other lepidopteran genomes. Friesen and Nissen (1990) reported the presence of the "TED" element from Trichoplusia ni, which contains three open reading frames flanked by LTRs. The third ORF is homologous to the gene for envelope fusion proteins (e. g., ORF 130 in LdNPV) in Class II baculoviruses. Its structure is similar to Drosophila endogenous retroviruses, including gypsy. We found that not only Trichoplusia but also Bombyx carries retrovirus-like elements. The EST and the whole-genome shotgun sequences seem to contain at least 5 families of retrovirus-like elements, whose final ORFs encode ENV-like proteins.
We also found 12 fragmental sequences of genomic DNA that show strong homology to mitochondrial DNA of Bombyx mori. This is the first evidence indocating the Bombyx genome has incorporated mitochondrial DNA.
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