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

Repetitious Element 1360 as a Target for Heterochromatin Formation in Drosophila Melanogaster

Mentor: Sarah Elgin From the Washington University Undergraduate Research Digest: WUURD, Volume 2, Issue 2, Spring 2007. Published by the Office of Undergraduate Research. Henry Biggs, Director of Undergraduate Research and Associate Dean in the College of Arts & Sciences; Joy Zalis Kiefer, Undergraduate Research Coordinator, Editor, and Assistant Dean in the College of Arts & Sciences; Kristin Sobotka, Co-editor

Host Response to Malignant Tumors in Drosophila melanogaster

Cancer is the abnormal growth of cells. This growth can kill by disrupting the normal function of its organ of residence or through long-range pathophysiological interactions with distant tissues. Despite the morbidity and mortality associated with cancer, the mechanisms underlying these lethal interactions have remained elusive.We have established a Drosophila tumor model to explore the poorly-understood mechanisms of tumor-host interactions. Using a classic technique, we transplanted larval tumors into adult flies and investigated the effects imposed on host tissues. We find that only 5 days post-transplantation, malignant fly tumors induce robust wasting of muscle, adipose and gonadal tissues. Interestingly, these wasting phenotypes recapitulate key characteristics of the enigmatic cancer cachexia suffered by about half of human cancer patients. We have identified the Insulin Growth Factor Binding Protein (IGFBP) homolog ImpL2 as key mediator of these cachexia-like phenotypes. This factor is secreted specifically by malignant tumors and is both necessary and sufficient for tissue wasting. Consistent with its role as an insulin antagonist, tumor-secreted ImpL2 interrupts systemic insulin signaling to induce insulin resistance, resulting in the cachexia-like wasting of peripheral host tissues.Our work demonstrates that this Drosophila model lends itself to the dissection of complex tumor-host interactions, such as cachexia. We have also used this model to investigate other important features of tumor-host interactions, including metastasis, bloating, immune response and lethality. The genetic manipulability of this system has facilitated the identification of a critical factor mediating the observed cachexia-like phenotypes and can now be used to explore other contributors to the tumor-induced systemic wasting or the molecular mechanisms underlying other important tumor-host interactions

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