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The Molecular Genetic Research on the Oily Mutant in Silkworms, Bombyx mori.

Haokun Zhang (D1)

As the uric acid, one of the end products of nitrogen metabolism in the silkworm, is mainly synthesized in the fat body and incorporated into epidermal cells via the hemolymph and accumulated as granules, the color of the normal silkworms is white and opaque. At the same time, the genetic absence or insufficiency of the urate granules in the integument leads to striking phenotype with translucent larval skin, referred as “oily” mutants (Figure 1). The reasons of abnormality of the uric acid metabolism in the silkworms, causing the oily-paper-like phenotype, can be divided into 3 kinds: (1) inability of uric acid biosynthesis; (2) inability of uric acid transportation; (3) inability of urate granules construction. Recently, the researches on the oily mutants highlight the tight relationship between urate granules and membrane transportation.

I performed the genetic study to find the reason for oily mutant via positional cloning and other molecular biological methods, using the two different oily backcross silkworm strains of one candidate gene mutation. Now, as my investigation processed, there would be a clear explanation for the mechanism of some oily phenotype in silkworm in near future.

The recent researches, mainly focused on the inability of urate granules construction, suggested that the mutation of the orthologs of LROs (Lysosome-Related Organelles) in the silkworms could lead to the oily-paper-like phenotype. In addition, reverse genetic study approaches, such as the knockdown of LROs-silkworm-orthologs carried by my colleague, Miss Nakashima, could also cause the oily mutant in the wild type successfully. Conclusively, both of the cis-genetic and reverse genetic investigation domesticate that the mutation of the LROs genes have directly relation with the silkworm’s oily mutant phenotype.

Easily observable oily mutant silkworms with various degrees of translucency are thought to be outstanding model animals for the investigation of the uric acid metabolism abnormality. The molecular genetic study on these silkworms with striking phenotype can extremely contribute the further and deeper understanding of the uric acid metabolism and the membrane transportation. In the future, at the same time of elucidating the molecular mechanism of abnormal LROs genes cause the translucent skins, I am also willing to find other genes responsible for the various oily-paper-like phenotype mutants.

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Figure 1: the oily mutant and wild type of the silkworm, Bombyx mori.