Proteome analysis on lethal effect of l 2 in the sex-linked balanced lethal strains of silkworm, Bombyx mori

The sex-linked balanced lethal (SLBL) strains of silkworm serve as an effective system for sex-control in silkworm. To gain comprehensive insight into the effect of one sex-linked balanced lethal gene l 2, comparative proteomic analysis was carried out between the survival embryos \(\left( {W^{ + l_1 } Z^{l_1 + l_2 } } \right)\) and lethal embryos \(\left( {W^{ + l_1 } Z^{ + l_1 l_2 } } \right)\) before the lethal stage. The lethal stage of l 2 was confirmed by observing the typical dead embryo morphology. The two genotype embryos before lethal stage were distinguished using polymorphic simple sequence repeats (SSR) markers closely linked to l 2 on the sex chromosome. Finally, 11 differentially expressed protein spots were successfully identified by MALDI-TOF/TOF mass spectrometry (MS). Among them, only 1 protein identified as heat shock protein 20.4 (HSP20.4) was up-regulated in the lethal embryos, while the other 10 were down-regulated. The up-regulation of HSP20.4 suggests that there may be abnormal polypeptides produced in the lethal embryos. The gene ontology (GO) annotation indicated those down-regulated proteins are involved in important biological processes including embryo development, nucleoside metabolism, tRNA splicing, translation and protein folding. The biological pathway analysis showed that those down-regulated proteins are mainly involved in spindle assemblage and morphogenesis. Based on our results, we suggest that the l 2 may be the mutant expressing abnormal polypeptides. Its expression has a negative effect on mitosis and morphogenesis processes. The death of the embryos may be caused by the accumulation of abnormal polypeptides and the handicap of cell proliferation and morphogenesis.