PHYSIOLOGICAL AND BIOCHEMICAL STUDIES ON EMBRYONIC DEVELOPMENT OF SILKWORMS

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Vitellins (Vns) were purified form the eggs of the two wild silkworm, Antheraea pernyi (Ap) and Antheraea yamamai (Ay) by Butyl-cellulofine chromatography, DE-52 cellulose column chromatography and hydroxyapatite column chromatography. Native molecular weight of ApVg is approximately 470000 as same as ApVn, while the molecular weights of AyVg and AyVn are 465000 and 450000, respectively. The amounts of Antheraea vitellogenin in hemolymph increased remarkably after spinning and kept constant concentration until the commencement of vitellogenesis. In vitro translation of RNA from fat body and immunoprecipitation of translation products using anti-Vn antiserum showed that the synthesis of Vgs occurred in the fat bodies after spinning but reduced remarkably after pupation.In an initial effort to understand the molecular mechanism of how-low temperature induces sorbitol dehydrogenase gene expression in diapause eggs of the silkworm, the sorbitol dehydrogenase gene was isolated from a Bombyx genomic library using a cDNA encoding the Bombyx homologue of mammalian sorbitol dehydrogenase as a probe. The gene extended for about 10 kb, consisting of eight exons and seven introns. AATTAA,instead of AATAAA,was localized in the upstream region of the polyadenylation site. Although a single copy of thie gene was present per haploid genome, 1.2kb and 1.1kb transcripts were found from yolk cells in diapause eggs and from larval fat body cells, respectively. The two major transcription initiation sites corresponding to both transcripts were localized at 355 and 226 base pairs upstream from the translation start site, indicating an alternative use of promoter. The 5'-upstream region of the gene contained a consensus sequence, TGA (A/T) AA (A/G/T), that has been found in insect genes expressed mainly in larval and pupal fat bodies.