Shotgun proteomic analysis on the embryos of silkworm Bombyx mori at the end of organogenesis.

Embryonic development of silkworm, Bombyx mori is a process of systematical expression of genes and proteins which is dominated by complex regulatory networks. To gain comprehensive insight into the molecular basis of embryonic development and its regulation mechanisms, the proteome profile of the B. mori embryos at the end of organogenesis (tubercle appearance stage, TA) was characterized using LTQ-Orbitrap mass spectrometer. Totally 963 proteins were identified with a false discovery rate (FDR) of 0.12%. They were involved in embryonic development, chemoreception, and stimuli response and so forth. The proteins with the largest number of identified unique peptides, implying their possibly higher abundance, were involved in heat shock response, lipid transport and metabolism, and apoptosis. It was consistent with the physiological status of embryo at the end of organogenesis. Many functionally important proteins were identified for the first time in B. mori embryo such as the progesterone receptor membrane component 2, antennal binding protein, sericotropin, and molting fluid carboxypeptidase A (MF-CPA). 253 (26.27%) specific proteins in TA versus labrum appearance stage (LA, four days before TA) embryos were identified, which were mainly associated with musculature, nervous system, and chemoreception system. They disclosed the differential temporal and spatial expression of proteins in the process of organogenesis. The relative mRNA levels of fifteen identified proteins in the two experimented stages were also compared using quantitative reverse transcription PCR (qRT-PCR) and showed some inconsistencies with protein expression. Gene Ontology (GO) annotation of the identified proteins showed that the most proteome representations were in the categories of "binding" and "catalytic" in molecular function, and "cellular process" and "metabolic process" in biological process.