Targeting of P-Element Reporters to Heterochromatic Domains by Transposable Element 1360 in Drosophila melanogaster.

Heterochromatin is a common DNA packaging form employed by eukaryotes to constitutively silence transposable elements. Determining which sequences to package as heterochromatin is vital for an organism. Here, we use Drosophila melanogaster to study heterochromatin formation, exploiting position-effect variegation, a process whereby a transgene is silenced stochastically if inserted in proximity to heterochromatin, leading to a variegating phenotype. Previous studies identified the transposable element 1360 as a target for heterochromatin formation. We use transgene reporters with either one or four copies of 1360 to determine if increasing local repeat density can alter the fraction of the genome supporting heterochromatin formation. We find that including 1360 in the reporter increases the frequency with which variegating phenotypes are observed. This increase is due to a greater recovery of insertions at the telomere-associated sequences (∼50% of variegating inserts). In contrast to variegating insertions elsewhere, the phenotype of telomere-associated sequence insertions is largely independent of the presence of 1360 in the reporter. We find that variegating and fully expressed transgenes are located in different types of chromatin and that variegating reporters in the telomere-associated sequences differ from those in pericentric heterochromatin. Indeed, chromatin marks at the transgene insertion site can be used to predict the eye phenotype. Our analysis reveals that increasing the local repeat density (via the transgene reporter) does not enlarge the fraction of the genome supporting heterochromatin formation. Rather, additional copies of 1360 appear to target the reporter to the telomere-associated sequences with greater efficiency, thus leading to an increased recovery of variegating insertions.

Malignant Drosophila tumors interrupt insulin signaling to induce cachexia-like wasting.

Tumors kill patients not only through well-characterized perturbations to their local environment but also through poorly understood pathophysiological interactions with distant tissues. Here, we use a Drosophila tumor model to investigate the elusive mechanisms underlying such long-range interactions. Transplantation of tumors into adults induces robust wasting of adipose, muscle, and gonadal tissues that are distant from the tumor, phenotypes that resemble the cancer cachexia seen in human patients. Notably, malignant, but not benign, tumors induce peripheral wasting. We identify the insulin growth factor binding protein (IGFBP) homolog ImpL2, an antagonist of insulin signaling, as a secreted factor mediating wasting. ImpL2 is sufficient to drive tissue loss, and insulin activity is reduced in peripheral tissues of tumor-bearing hosts. Importantly, knocking down ImpL2, specifically in the tumor, ameliorates wasting phenotypes. We propose that the tumor-secreted IGFBP creates insulin resistance in distant tissues, thus driving a systemic wasting response.