LAUSR

The cell nucleus is a highly organized environment containing various nuclear bodies or organelles that are involved in the metabolism of RNA. A few nuclear structures are known to associate with specific chromosomal loci to facilitate processing of RNA from these loci. Notably, the nucleolus associates with the nucleolar organizing region (NOR), which contains tandem repeats of rDNA; while the histone locus body (HLB) associates with the tandem repeats of histone gene loci. Here we describe the identification of a novel nuclear body (we termed satellite body) that associates with the chromosome four in Drosophila melanogaster. A doublestranded RNA binding protein Disco-interacting protein 1 (DIP1) forms nuclear bodies in transcriptionally active cells, but not in oocyte nuclei, spermatids, and cells during mitosis. DIP1 localizes to satellite bodies that decorate the fourth chromosomes in both germline and somatic cells. The Drosophila chromosome four contains a very high density of INE-1 transposable element sequences in the introns, which are processed into stable intronic sequence RNAs (sisRNAs). Mutation and overexpression of DIP1 show that DIP1 negatively regulates the abundance of INE-1 sisRNAs. Our results show that satellite bodies localize to chromosome four, and suggest that they function to regulate the levels of sisRNAs from intronicencoded INE-1 elements, which are present in high concentration in chromosome four in Drosophila. Our study provides insights to the compartmentalization of double-stranded RNA or sisRNA metabolism machineries in the nucleus.