Diapause-Related Gene Expression in Eggs of Multivoltine Bombyx mori L. Silkworm Races

Abstract

The diapause hormone has been identified as a major factor inducing diapause in silkworm, Bombyx mori L. However, the molecular mechanism controlling egg diapause in multivoltine silkworm remains unclear. In this study, an attempt is made to decipher molecular events during embryonic diapause in multivoltine silkworm. Using suppressive subtractive hybridization (SSH) 186 cDNA clones were isolated and sequenced from both diapause and non-diapause eggs wherein 29 diapause-related genes were identified and classified into six functional groups. The qPCR analysis confirmed the expression of 11 of these genes, wherein, three were upregulated during diapause and another seven during non-diapause, while, one gene remained unchanged. The gene expression profiles of diapause-induced and non-diapause eggs of multivoltine silkworm were also investigated at 18 and 30 h after oviposition using oligonucleotide microarrays containing 24,924 probes. Data analysis revealed upregulation of 638 genes and downregulation of 1136 genes at 18 h after oviposition. Further at 18 and 30 h after oviposition, 115 genes were stably upregulated, while 117 were stably downregulated. The annotated genes showing fold change of one and above were classified into seven functional groups, viz. immune, metabolism, stress, signal transduction, cell cycle, transcription, and apoptosis. The overall genes expressed at 18 h was higher than that at 30 h under both diapause and non-diapause conditions indicating that crucial biological processes for initiation or termination of diapause mechanism occur during 18 h time period.