Runt is the founding member of a family of transcriptional regulators known as the Runt domain family. In Drosophila embryos the Runt protein plays an important role in sex determination, neurogenesis, and segmentation. Vertebrate Runt domain proteins have been discovered to play important roles in the processes of hematopoesis and osteogenesis. In fact, mutations with the AML1 (Runx1) gene have been associated with human leukemia and mutations in CbfA1 (Runx2) lead to defects associated with cleidocranial dysplasia.
The Drosophila embryo provides an excellent model to study the mechanism of transcriptional regulation by the Runt protein. In some instances Runt serves as an activator of transcription, in others it plays a role in transcriptional repression. By describing how Runt interacts with various other genes one can gain greater understanding of the mechanisms governing the activity of Runt domain proteins.
The focus of this project was to study regulation of the expression of Sloppy-paired (slp). Normally, slp is expresses in fourteen stripes along the anterior-posterior body axis, one stripe for each segment. Expression of the odd-numbered slp stripes requires Runt as well as another transcription factor, Odd-paired (Opa). Interestingly Runt and Opa are also present in even-numbered segments, but in cells that do not express slp. Previous results suggest that activation of slp by Runt and Opa is blocked by the presence of the Fushi-tarazu (Ftz) transcription factor. Two experiments were performed to study the relationship between Ftz and Slp expression. Both relied on the NGT (nanos-GAL4-tubulin) system to drive ectopic expression of genes.
In the first experiment outcrosses were performed to produce Drosophila embryos that were mutant for ftz and ectopically expressed both Runt and Opa. Approximately 25% of the embryos were expected to be ftz mutants and half would express Runt and Opa. Approximately 12.5% of the embryos examined will be expected to show the consequences of ectopically expressing Runt and Opa in the absence of Ftz. In the second experiment flies were bred to ectopically express runt, opa, and hairy (h)- a gene which is able to repress ftz expression.
To visualize the expression of slpin situ hybridization was performed with probes to detect the presence of slp mRNA. The results of the in situ will reveal the validity of the hypothesis.
This work was supported by the Simons Foundation and a grant from the National Science Foundation.