Androcam, a Drosophila calmodulin-related protein, is expressed specifically in the testis and decorates loop kl-3 of the Y chromosome

Abstract

The Drosophila genome encodes a protein that is 68% identical to Drosophila calmodulin (Cam). We show here that this Cam-related gene is specifically expressed in the germ-line of the testis, leading to the name Androcam (Acam). Early in spermatogenesis Acam accumulates on one of the chromatin loops of the Y chromosome, kl-3. This association with kl-3 may indicate an RNA processing-related role for Acam and/or could reflect an unusual storage/assembly function hypothesized for the Y loops. After meiosis Acam is detectable in developing sperm tail cytoplasm, where at least some of the protein is not tightly associated with tubulin. Late in spermiogenesis, some Acam staining overlaps the periphery of the investment cones, actin-containing structures hypothesized to support the motor function for cytoplasmic stripping of the tail. Acam cannot be detected in mature sperm by immunolocalization, but immunoblotting established that Acam is present in sperm stored in mated females, suggesting epitope masking during final maturation. Proteins more related to Acam than Cam are present in the testes of other Drosophila species and a mammalian species, the mouse.