Background: The silkworm Bombyx mori is a lepidopteran insect with four developmental stages: egg, larva (caterpillar), pupa, and adult. The hemolymph of the silkworm is in an open system that circulates among all organs, and functions in nutrient and hormone transport, injury, and immunity. To understand the intricate developmental mechanisms of metamorphosis, silkworm hemolymph from different developmental stages, including the 3rd day of fifth instar, the 6th day of fifth instar, the 3rd day of pupation, the 8th day of pupal stage and the first day of the moth stage, was investigated by two-dimensional electrophoresis and mass spectrometry.
Results: Two-dimensional polyacrylamide gel electrophoresis showed that from the larval to moth stages, silkworm hemolymph proteins changed markedly. Not only did major proteins such as SP1, SP2, and the 30 K lipoprotein change, but other proteins varied greatly at different stages. To understand the functions of these proteins in silkworm development, 56 spots were excised from gels for analysis by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). We identified 34 proteins involved in metamorphosis, programmed cell death, food digestion, metabolism, and nutrient storage and transport. Most proteins showed different expression at different stages, suggesting functions in development and metamorphosis. An abundance of proteins related to immunity were found, including hemolin, prophenoloxidase, serine proteinase-like protein, paralytic peptide-binding protein, and protease inhibitor.
Conclusions: Proteomics research not only provides the opportunity for direct investigation of protein expression patterns, but also identifies many attractive candidates for further study. Two-dimensional maps of hemolymph proteins expressed during the growth and metamorphosis of the silkworm offer important insights into hemolymph function and insect metamorphosis.