A novel RNA helicase-like protein during early embryonic development in silkworm Bombyx mori: molecular characterization and intracellular localization.

In order to understand the molecular mechanism of development during early embryogenesis in diapause and non-diapause of the silkworm, mRNA from diapause and non-diapause eggs was compared using the differential display technique. We cloned the full length of a cDNA encoding a novel RNA helicase-like (RHL) protein by the RACE method using a cDNA fragment which was one of the specific cDNAs in the non-diapause eggs. A BLAST search using the predicted amino acid sequence of RHL revealed a low homology (21-25% identity of its partial length) with that of the DEAD-box RNA helicase. Gene expression of the RHL gene of the diapause and non-diapause eggs was investigated by RT-PCR until 60h after oviposition. Amplified RHL cDNA was observed through all the stages in the non-diapause eggs, while in the diapause eggs, cDNA was found in eggs 0-12h after oviposition but disappeared 24-60h after oviposition. When the diapause eggs were activated by HCl treatment after chilling at 4 degrees C for 6 days from 48h after oviposition (artificial diapause termination), cDNA was observed from 12h after HCl treatment. We also investigated the immunohistochemical distribution and localization of RHL in non-diapause eggs using anti-recombinant His-tag RHL antiserum. RHL was distributed in blastoderm cells and yolk cells and was localized in the nucleus and the cytosol of yolk cells. These data suggest that RHL has an important role in the early embryo of the silkworm.