| Budget Amount *help |
¥3,800,000 (Direct Cost: ¥3,800,000)
Fiscal Year 2006: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2005: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2004: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Research Abstract |
To understand the differentiation mechanism of lepidopteran-specific dimorphic sperm formation, the function of Sex-lethal (Sxl) has been investigated. Upon cloning two isoforms for Sxl cDNA in Bombyx, named BmSxl-L and BmSxl-S. We found that the only difference between these two isoforms is in the length of the N-terminus. To understand the difference between Bm-Sxl-L and Bm-Sxl-S, in collaboration with Prof. Traut, the exon-intron structure was determined. As a result, alternative splicing creates the different lengths of the L and S type cDNAs.
In germline sex determination of Drosophila, Sxl is not a master switch gene but indispensable for oogenesis. However, BmSxl is mainly expressed during spermatogenesis. Surprisingly, BmSxl-L is expressed in cytoplasm of spermatocyte for nucleate eupyrene sperm, whereas BmSxl-S is expressed in nuclei of spermatocyte for anucleate apyrene sperm. The distinct expression pattern of each BmSxl isoform corresponds well to the developmental stage for the transition from eupyrene to apyrene spermatogenesis. Thus, it appears that BmSxl controls the eupyrene-apyrene sperm dimorphism, which is an evolutionary novelty of lepidopteran insects. In the lineage of Lepidoptera, at least in Ditrisia, Sxl could gaine a novel function in spermatogenesis, especially in the production of apyrene sperm. The ancient function of Sxl gene was in the germline and that in lineage of Lepidoptera, Sxl gained a novel function related to the eupyrene-apyrene sperm dimorphism, and further, during the evolution of genus Drosophila Sxl gained a novel function of somatic sex determination.
As an initial step to provide a direct evidence of Sxl function in Lepidoptera, we have establish germ-line transformation of silkworm.
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