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Transgenic analysis of the BmBLOS2 gene that governs the translucency of the larval integument of the silkworm, Bombyx mori


T. Shimada, Department of Agricultural and Environmental Biology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan. Tel.: + 81 3 5841 8124; fax: + 81 35841 8011; e-mail:


The larval integument of the silkworm, Bombyx mori, is opaque because urate granules accumulate in the epidermis. Although the biosynthetic pathway of uric acid is well studied, little is known about how uric acid accumulates as urate granules in epidermal cells. In the distinct oily (od) mutant silkworm, the larval integument is translucent because of the inability to construct urate granules. Recently, we have found that the od mutant has a genomic deletion in the B. mori homologue of the human biogenesis of lysosome-related organelles complex1, subunit 2 (BLOS2) gene (BmBLOS2). Here, we performed a molecular and functional characterization of BmBLOS2. Northern blot analysis showed that BmBLOS2 was ubiquitously expressed in various tissues. We analysed the structure of a newly isolated mutant (odB) allelic to od and found a premature stop codon in the coding sequence of BmBLOS2 in this new mutation. Moreover, the translucent phenotype was rescued by the germ-line transformation of the wild-type BmBLOS2 allele into the od mutant. Our results suggest that BmBLOS2 is responsible for the od mutant phenotype and plays a crucial role in biogenesis of urate granules in the larval epidermis of the silkworm. The relationships amongst Hermansky–Pudlak syndrome (HPS) genes in mammals, granule group genes in Drosophila and translucent mutant genes in B. mori are discussed.