Upregulated proteins associated with fibroin synthesis in posterior silk glands of Antheraea pernyi fifth instar larvae

Antheraea pernyi is a typical wild silkworm with larval silk glands specific for the synthesis and secretion of silk proteins. We examined changes in the protein profile in the posterior section of the silk glands on days 1 and 4 of the last larval instar. Two-dimensional gel electrophoresis over the pH range of 4–7 followed by silver staining revealed about 350 protein spots. Twenty-three proteins upregulated on day 4 were analyzed using matrix-assisted laser desorption/ionization time-of-flight/time-of-flight (MALDI-TOF/TOF). Search for homologous sequences in NCBI databases identified seven proteins probably involved in the regulation of transcription, translation, and general cell metabolism. Among these, glutathione S-transferase theta (GSTT) and ribosomal protein L8 (RPL8) were selected for investigations at the mRNA level. Real-time quantitative PCR showed that the expression of GSTT peaked on day 4, whereas that of RPL8 peaked on day 3, confirming the upregulation of these proteins during the last larval instar. These results show that expressions of GSTT and RPL8 may play a role in fibroin synthesis in A. pernyi.