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

Abstract

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 (od(B) ) 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.

Mutations in an amino acid transporter gene are responsible for sex-linked translucent larval skin of the silkworm, Bombyx mori

“…In the mutants oq (q-translucent) and og (giallo ascoli translucent), xanthine dehydrogenase activity is lost, and hence, the insect cannot synthesize uric acid (Komoto, 2002;Komoto et al, 2003). Fujii et al (2008Fujii et al ( , 2010 reported that the od (distinct translucent) gene encodes a Bombyx homolog of the BLOS2 subunit of the human biogenesis of lysosome-related organelles complex-1 (BLOC-1), which is related to a genetic disease, the HermanskyePudlak syndrome (Wei, 2006). Ito et al (2009) showed that a 25-bp insertional mutation in the BmVarp gene causes the ow (waxy translucent) phenotype.…”

Can the silkworm (<i>Bombyx mori</i>) be used as a human disease model?

“…The common phenotype of these mutants is translucent larval skin (22). Eight genes have been identified as causative genes in translucent larval skin mutants (23)(24)(25)(26)(27)(28)(29)(30)(31). These genes are involved in the synthesis or uptake of uric acid.…”

The CRISPR/Cas System mediates efficient genome engineering in Bombyx mori

“…In B. mori, ZFN-and TALENmediated gene mutagenesis targeting BmBLOS2 was reported [7,8]. BmBLOS2 is the homolog of the human biogenesis of lysosome-related organelles complex 1, subunit 2 gene, and is responsible for urate granule synthesis in B. mori larval epidermis [9]. When BmBLOS2 function is compromised, the larval integument is transformed from opaque to translucent, generating the oily skin phenotype (OSP).…”