First report on transferrin in the silkworm, Antheraea mylitta, with a putative role in antioxidant defense: Insights from proteomic analysis and immunodetection.

Transferrin is a highly conserved multifunctional protein involved in iron metabolism, oxidative stress and immune response. However, very little is known about its context-dependent functional role in insects. The present study adopts a proteomic approach to identify an abundant hemolymph protein of silkworm (Antheraea mylitta) as transferrin. SDS-PAGE coupled to LC-MS/MS was followed to identify this protein (75.7 kDa) in the advanced larvae of A. mylitta as transferrin (AmTsf). Antibody developed against this protein enabled us to determine its tissue-specific expression and functional relevance during development. Its immunodetection was optimized by western blotting, immunohisto- and cytochemistry in the larval and pupal tissues of this insect. AmTsf exhibited a considerable homology with that of other related insects. It was found to be expressed constitutively in hemolymph, fat body, midgut and silk gland of this insect during development. Abundance of transferrin in the hemolymph of this species and its upregulation in response to oxidant challenges indicated its tissue-specific role in the antioxidant protection. The present work adds to the existing knowledge of multiple roles of transferrin in insects and provides an insight into a relatively unexplored aspect of iron-associated HO metabolism and redox homeostasis in the apparent absence of catalase and glutathione peroxidase. Therefore, A. mylitta can be an attractive acatalasemic model for the study of in vivo redox regulation. In addition, this study provides a novel hypothesis to explore the role of transferrin in limiting oxidative stress during larval rearing of silkworm.