A mutant affecting the crystal cells in Drosophila melanogaster

Abstract

Black cells (Bc, 2-80.6±) mutant larvae of Drosophila melanogaster have pigmented cells in the hemolymph and lymph glands. In this report we present evidence that these melanized cells are a mutant form of the crystal cells, a type of larval hemocyte with characteristic paracrystalline inclusions. Bc larvae lack crystal cells. Furthermore, the distribution pattern of black cells in Bc larvae parallels that of experimentally-blackened crystal cells in normal larvae (phenocopy).In Bc/Bc zygotes black cells appear during mid embryonic development but in Bc + / Bc zygotes pigmented cells are not found until late in the first larval instar.Crystal cells are present in the heterozygous larvae until this time, and paracrystalline inclusions can be seen in some of the cells undergoing melanization in these larvae.The rate of phenol oxidase activity in Bc + / Bc larval cell-free extracts is less than half that of Bc + / Bc + extracts whereas enzyme activity is undetectable in Bc/Bc larvae. We propose that the Bc + gene product is required for maintaining the integrity of the paracrystalline inclusions; in Bc/Bc larvae either the product is absent or nonfunctional so an effective contact between substrate and enzyme results in melanization of the cells.Phenol oxidase itself is either destroyed or consumed in the melanization process accounting for the absence of enzyme activity in Bc/Bc larvae. These studies confirm that the crystal cells store phenolic substrates and are the source of the hemolymph phenol oxidase activity in the larva of D. melanogaster .