A larval serum protein of the silkworm, Bombyx mori: cDNA sequence and developmental specificity of the transcript

The Bombyx mori larval serum protein (BmLSP) is a major component of larval hemolymph proteins until early in the last instar. The cDNA for BmLSP was cloned from a library constructed from fat body RNA of penultimate instar larvae, and the complete nucleotide sequence of the 909 base pair cDNA insert was determined. The deduced 262 amino acid polypeptide included a 16 amino acid residue signal peptide and a 15 amino acid sequence prosegment. A homology search showed that BmLSP has significant similarity with microvitellogenin of Manduca sexta and the 30K proteins of B. mori. Tissue distribution and developmental profile of BmLSP mRNA were analyzed by northern hybridization. BmLSP mRNA was abundant in fat body but not detected in midgut and silk gland. BmLSP mRNA was present during the feeding periods of the fourth and fifth instar larvae, but absent during the larval molt and after the onset of cocoon spinning.