The Ribosomal Protein RpL22 Interacts In Vitro with 5'-UTR Sequences Found in Some Drosophila melanogaster Transposons.

Mobility of eukaryotic transposable elements (TEs) are finely regulated to avoid an excessive mutational load caused by their movement. The transposition of retrotransposons is usually regulated through the interaction of host- and TE-encoded proteins, with non-coding regions (LTR and 5'-UTR) of the transposon. Examples of new potent cis-acting sequences, identified and characterized in the non-coding regions of retrotransposons, include the insulator of gypsy and Idefix, and the enhancer of ZAM of Drosophila melanogaster. Recently we have shown that in the 5'-UTR of the LTR-retrotransposon ZAM there is a sequence structured in tandem-repeat capable of operating as an insulator both in Drosophila (S2R+) and human cells (HEK293). Here, we test the hypothesis that tandem repeated 5'-UTR of a different LTR-retrotransposon could accommodate similar regulatory elements. The comparison of the 5'-UTR of some LTR-transposons allowed us to identify a shared motif of 13 bp, called Transposable Element Redundant Motif (TERM). Surprisingly, we demonstrated, by Yeast One-Hybrid assay, that TERM interacts with the D. melanogaster ribosomal protein RpL22. The Drosophila RpL22 has additional Ala-, Lys- and Pro-rich sequences at the amino terminus, which resembles the carboxy-terminal portion of histone H1 and histone H5. For this reason, it has been hypothesized that RpL22 might have two functions, namely the role in organizing the ribosome, and a potential regulatory role involving DNA-binding similar to histone H1, which represses transcription in Drosophila. In this paper, we show, by two independent sets of experiments, that DmRpL22 is able to directly and specifically bind DNA of Drosophila melanogaster.

The Drosophila simulans Genome Lacks the crystal-Stellate System.

The cry-Ste system is a genetic interaction system between heterochromatin and euchromatin in Drosophila melanogaster, regulated via the piRNA pathway. Deregulation of this system leads to meiotic defects and male sterility. Although the cry-Ste system is peculiar to D. melanogaster, ancestors of Ste and Su(Ste) elements are present in the three closely related species, D. simulans, D. sechellia, and D. mauritiana. The birth, evolution, and maintenance of this genetic system in Drosophila melanogaster are of interest. We investigate the presence of sequences homologous to cry and Ste elements in the simulans complex and describe their chromosomal distribution. The organization and expression of cry- and Ste-like sequences were further characterized in the D. simulans genome. Our results allow us to conclude that the cry-Ste genetic interaction system is absent in the D. simulans genome.

Cytological heterogeneity of heterochromatin among 10 sequenced Drosophila species.

In Drosophila chromosomal rearrangements can be maintained and are associated with karyotypic variability among populations from different geographic localities. The abundance of variability in gene arrangements among chromosomal arms is even greater when comparing more distantly related species and the study of these chromosomal changes has provided insights into the evolutionary history of species in the genus. In addition, the sequencing of genomes of several Drosophila species has offered the opportunity to establish the global pattern of genomic evolution, at both genetic and chromosomal level. The combined approaches of comparative analysis of syntenic blocks and direct physical maps on polytene chromosomes have elucidated changes in the orientation of genomic sequences and the difference between heterochromatic and euchromatic regions. Unfortunately, the centromeric heterochromatic regions cannot be studied using the cytological maps of polytene chromosomes because they are underreplicated and therefore reside in the chromocenter. In Drosophila melanogaster, a cytological map of the heterochromatin has been elaborated using mitotic chromosomes from larval neuroblasts. In the current work, we have expanded on that mapping by producing cytological maps of the mitotic heterochromatin in an additional 10 sequenced Drosophila species. These maps highlight 2 apparently different paths, for the evolution of the pericentric heterochromatin between the subgenera Sophophora and Drosophila. One path leads toward a progressive complexity of the pericentric heterochromatin (Sophophora) and the other toward a progressive simplification (Drosophila). These maps are also useful for a better understanding how karyotypes have been altered by chromosome arm reshuffling during evolution.

Evidence of the Physical Interaction between Rpl22 and the Transposable Element Doc5, a Heterochromatic Transposon of Drosophila melanogaster.

Chromatin is a highly dynamic biological entity that allows for both the control of gene expression and the stabilization of chromosomal domains. Given the high degree of plasticity observed in model and non-model organisms, it is not surprising that new chromatin components are frequently described. In this work, we tested the hypothesis that the remnants of the Doc5 transposable element, which retains a heterochromatin insertion pattern in the melanogaster species complex, can be bound by chromatin proteins, and thus be involved in the organization of heterochromatic domains. Using the Yeast One Hybrid approach, we found Rpl22 as a potential interacting protein of Doc5. We further tested in vitro the observed interaction through Electrophoretic Mobility Shift Assay, uncovering that the N-terminal portion of the protein is sufficient to interact with Doc5. However, in situ localization of the native protein failed to detect Rpl22 association with chromatin. The results obtained are discussed in the light of the current knowledge on the extra-ribosomal role of ribosomal protein in eukaryotes, which suggests a possible role of Rpl22 in the determination of the heterochromatin in Drosophila.