Toward a detailed molecular characterization of the crystal region on the Y chromosome

The crystal-Stellate system is one of the most studied examples of heterochromatin-euchromatin interaction in Drosophila melanogaster. The loss of the heterochromatic h11 region on the Y chromosome, called “crystal” region (or Suppressor of Stellate, results in the production of crystalline aggregates in spermatocytes due to the expression of the Stellate euchromatic mRNA, from 12 E-F region on the X chromosome, coding for the Stellate protein that is the main components of crystals. The crystal-Stellate interaction represents the first natural case of a piRNA-mediated regulation in Drosophila melanogaster. Many piRNAs corresponding to crystal sequences have been identified in testes and they are supposed to silence Stellate euchromatic sequences in normal conditions. The piRNA pathway also silences the transposable elements (TEs), protecting genomes from potentially deleterious effects of their activation maintaining the genome stability in gonads and in other somatic tissues. In order to acquire more information about the molecular basis of the crystal-Stellate regulation, we started a detailed genomic analysis of the crystal sequences contained in the Release 6 of the Drosophila genome and we identified two main regions containing crystal sequences and they exhibit different molecular structures. Recently new sequences from the heterochromatin of the Y chromosome have been published and we put together all the available information to describe in details the organization of the regions containing the crystal repeats in order to get more clear information on their role in regulating the Stellate sequences.