| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2006: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2005: ¥3,000,000 (Direct Cost: ¥3,000,000)
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| Research Abstract |
In the silkworm Bombyx mori (female, ZW ; male, ZZ), femaleness is determined by the presence of a single W chromosome, irrespective of the number of autosomes or Z chromosomes. The W chromosome is devoid of functional genes, except the putative female-determining gene (Fem). To understand these interesting features of the W chromosome, it is necessary to analyze the W chromosome at the molecular biology level. To the present, we have identified 12 W-specific RAPD markers, and with the exception of oneRAPD marker, all of the deduced amino acid sequences of these W-specific RAPD markers show similarity to previously reported mino acid sequences of retrotransposable elements from various organism. After constructing a genomic DNA lambda phage library of B.mori we obtained two lambda phage clones, one containing the W-Kabuki RAPD sequence and one contining the W-Samurai RAPD sequence and found that these DNA sequences comprised nested structures of many retrotransposable elements. To further analyze the W chromosome, we obtained 14 W-specific bacterial artificial chromosome (BAC) clones from three BAC libraries and subjected these clones to shotgun sequencing. The resulting assembly of sequences did not produce a single contiguous sequence due to the presence of many retrotransposable elements. Therefore, we coupled PCR with shotgun sequencing. Through these analyses, we found that many long terminal repeat (LTR) and non-LTR retrotransposons, retroposons, DNA transposons and their derivatives, have accumulated on the W chromosome as strata. These results strongly indicate that retrotransposable elements are the main structural component of the W chromosome.
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