Abstract
To clarify the molecular mechanisms of silkworm diapause, it is necessary to investigate the molecular basis at protein level. Here, the spectra of peptides digested from silkworm diapause and non-diapause eggs were obtained from liquid chromatography tandem mass spectrometry (LC-MS/MS) and were analyzed by bioinformatics methods. A total of 501 and 562 proteins were identified from the diapause and non-diapause eggs respectively, of which 309 proteins were shared commonly. Among these common-expressed proteins, three main storage proteins (vitellogenin precursor, egg-specific protein and low molecular lipoprotein 30 K precursor), nine heat shock proteins (HSP19.9, 20.1, 20.4, 20.8, 21.4, 23.7, 70, 90-kDa heat shock protein and heat shock cognate protein), 37 metabolic enzymes, 22 ribosomal proteins were identified. There were 192 and 253 unique proteins identified in the diapause and non-diapause eggs respectively, of which 24 and 48 had functional annotations, these unique proteins indicated that the metabolism, translation of the mRNA and synthesis of proteins were potentially more highly represented in the non-dipause eggs than that in the diapause eggs. The relative mRNA levels of four identified proteins in the two kinds of eggs were also compared using quantitative reverse transcription PCR (qRT-PCR) and showed some inconsistencies with protein expression. GO signatures of 486 out of the 502 and 545 out of the 562 proteins identified in the diapause and non-diapause eggs respectively were available. In addition, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed the Metabolism, Translation and Transcription pathway were potentially more active in the non-dipause eggs at this stage.
Highlights
Diapause is a special physiological state of arrested development by many insects to avoid unfavorable environments such as low temperature, drought or food shortage and to synchronize their life cycles to these changes [1,2]
In Bombyx mori, embryonic diapause is determined by a diapause hormone that is secreted by the suboesophageal ganglion (SG) of the mother moth during the pupal period to act on her developing ovaries and is responsible for induction of embryonic diapause of the silkworm, Bombyx mori [4,5]
To understand the functions of the proteins we identified, the protein sequences were queried against the InterPro databases and the resultant proteins were functionally categorized based on universal gene ontology (GO) annotation terms using the online GO tool Web Gene Ontology Annotation Plot (WEGO) [38,66]
Summary
Diapause is a special physiological state of arrested development by many insects to avoid unfavorable environments such as low temperature, drought or food shortage and to synchronize their life cycles to these changes [1,2]. Diapause is widespread among insects and can occur at any stage of the life cycle, i.e., adult, pupa, larva or egg, and each species enters diapause at fixed stages. In the silkworm Bombyx mori, the development of diapausedestined embryos is arrested during the G2 cell cycle stage immediately after formation of the cephalic lobe and telson and sequential segmentation of the mesoderm [3]. The embryos are competent to resume development at 25uC and cells enter the M phase; Cell division in the embryos resumes [3]
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