Alejandra Figueroa-Clarevega

REPETITIOUS ELEMENT 1360 AS A TARGET FOR HETEROCHROMATIN FORMATION IN DROSOPHILA MELANOGASTER. Alejandra Figueroa-Clarevega¹, Karmella Haynes¹, Kathryn Huisinga¹, Jo Wuller¹, Stephen McDaniel¹, Shachar Shimonovich¹, Amy Wu¹, Sarah C.R. Elgin¹. Department of Biology, Washington University in St. Louis, St. Louis, MO.¹

Drosophila melanogaster has served as an excellent model for the study of chromatin packaging. It has been particularly useful in differentiating between euchromatin and heterochromatin, which impact levels of gene expression. Most actively transcribed genes are found in euchromatin; on the other hand, heterochromatin is the form of packaging associated with gene silencing. Proximity to heterochromatin has the ability to induce PEV (Position Effect Variegation), in which a reporter gene is silenced in some of the cells where it is normally active. Earlier work has suggested that the repetitious element 1360, which is enriched in heterochromatic domains, can serve as an initiation site for heterochromatin formation in the fourth chromosome (Sun et al. 2004. Mol. Cell Bio. 24:8210). With this in mind, a P-element construct was designed containing one or four copies of 1360 upstream of an hsp70-driven white reporter to test whether this repetitious element is capable of initiating heterochromatin formation. This construct was injected into Drosophila embryos and transformants carrying the transgene were recovered. To generate additional lines, an X-chromosome insertion line was used in a cross to mobilize the P-element. A total of 5,000 males were screened for mobilizations. Without the 1360 element upstream of hsp70-white, only 1% of the lines recovered from previous P-element mobilization screens were variegating. We have observed that with one copy of 1360, 4% of the recovered lines are variegating; with four copies of 1360, 12% of the recovered lines are variegating. These results suggest that increasing copies of 1360 increase the likelihood of initiating heterochromatin formation. Pericentric, telomeric and chromosome four heterochromatin are known to induce PEV; we are currently mapping the distribution of the insertion sites to determine whether increased 1360 copy number allows ectopic heterochromatin formation outside of these regions. Supported by a WU/HHMI Fellowship to A.F.-C. and NIH grants GM68388 and GM73190 to SCRE.