Differential regulation of sloppy-paired-1 transcription initiation and elongation by Runt and Even-skipped during Drosophila segmentation. Kimberly Bell^1,3, Saiyu Hang^2,3, J. Peter Gergen³. 1) Graduate Program in Genetics; 2) Graduate Program in Biochemistry and Structural Biology; 3) Department of Biochemistry and Cell Biology and the Center for Developmental Genetics Stony Brook University, Stony Brook, NY 11794-5215.

   The initial metameric expression pattern of the sloppy-paired-1 (slp1) gene in the Drosophila blastoderm embryo is generated through two cis-regulatory elements, termed PESE and DESE for proximal and distal early stripe elements. These enhancers act in a non-additive manner to integrate inputs from distinct combinations of the pair-rule transcription factors Runt, Even-skipped (Eve), Fushi-tarazu (Ftz) and Odd-paired (Opa) resulting in fourteen two cell wide stripes in the segmented region of the embryo. This pattern consists of seven repetitive units, each comprised of four different cellular contexts (I-IV) of slp1 transcription regulation. Slp1 is actively transcribed in type II and IV cells, each with important contributions from Opa. In type I cells, slp1 is not expressed due to repression by Eve. Chromatin immuno-precipitation (ChIP) experiments indicate this is due to an Eve-dependent block to transcription elongation mediated by PESE that involves antagonizing P-TEFb recruitment to the promoter. Similarly, Runt+Ftz act to repress expression in type III cells by blocking transcription elongation mediated by DESE. PESE activity is also repressed by Runt in type III cells. Interestingly, this repression involves blocking PESE dependent recruitment of PolII and the initiation of transcription, a different mechanism than DESE mediated repression in the same cellular context. This effect of Runt on PESE is consistent with a previous proposal that Runt prevents functional interactions between PESE and the slp1 promoter. We will report results of experiments to determine if the distinct slp1 expression states are reflected in changes in chromosome conformation involving different physical contacts between the promoter and other regions in response to regulatory inputs from Runt and other pair-rule transcription factors.