Occurrence of ommochrome-containing pigment granules in the central nervous system of the silkworm, Bombyx mori

Dark-red pigment granules were found in the brain and ganglion of the norma l strain of the silkworm, Bombyx mori, by light microscopy. No other pigmen tation was seen in the brain or ganglia. Electron microscopy showed that th e granules were electron-dense. The granules were similar to the ommochrome -containing pigment granules that are present in the epidermal cells of the quail mutant, as previously reported. The pigment in the larval central ne rvous system (CNS) of the normal silkworm was identical to the ommin standa rd with respect to the absorption spectrum, the infrared spectrum, and the R-f value in thin-layer chromatography (TLC). After acid hydrolysis of the pigment, 3-hydroxykynurenine was detected by TLC. The pigment granules in t he CNS contained mainly ommin. An ommochrome-binding protein was also detec ted in the CNS by in vitro binding studies and Western blotting. The ommoch rome granules may have an important function in the CNS of the silkworm. (C ) 2000 Elsevier Science Inc. All rights reserved.