Institute of Agrobiological Sciences, NARO

Silkworm Genomics


Silkworm belongs to the group of insects that includes butterfly and moth, particularly the family of moths known as Bombycidae. Silkworm was first domesticated in ancient China about 5000 years ago from a wild silkmoth known as "kuwako". Subsequent domestication and breeding led to the development of improved and superior varieties. The silkworm larva hardly moves so that even if the food is depleted, silkworm can survive until food becomes available. An adult moth that comes out of the cocoon has a pair of wings which is almost degenerated and could not function for flying. For this reason, the silkworm is entirely dependent on humans for survival.

Silkworm Genome Research Program (SGP)

Silkworm genome sequencing


A threefold shotgun sequencing of the silkworm (Bombyx mori) genome was performed to obtain a draft sequence and establish a basic resource for comprehensive genome analysis. The sequence data derived from whole-genome shotgun (WGS) sequencing were assembled into 49,345 scaffolds that span a total length of 514 Mb including gaps and 387 Mb without gaps. Analysis of the WGS data revealed that the silkworm genome contains many repetitive sequences with an average length of less than 500 bp derived from truncated transposons, which are interspersed at 2.5- to 3-kb intervals throughout the genome. This pattern suggests that silkworm may have an active mechanism that promotes removal of transposons from the genome. We also found evidence for insertions of mitochondrial DNA fragments at 9 sites. A search for Bombyx orthologs to Drosophila genes controlling sex determination in the WGS data revealed 11 Bombyx genes and suggested that the sex-determining systems differ profoundly between the two species.


Silkworm genomics databases and resources


To build a foundation for the complete genome analysis of Bombyx mori, we have constructed an EST database. Because the gene expression patterns highly depend on tissues as well as developmental stages, we analyzed many cDNA libraries prepared from various tissues and different developmental stages to cover the entire set of Bombyx genes. So far, the Bombyx EST database contains 35,000 ESTs from 36 cDNA libraries, which are grouped into about 11,000 nonredundant ESTs with the average length of 1.25 kb. All sequenced ESTs are compiled into the Bombyx EST database, named KAIKObase. Analysis tools have also been constructed such asBLAST, KAIKOGAAS etc.

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