| الوصف: |
Transcription factor AP-2 family genes have important roles in limb, orofacial and nervous system development in vertebrates and Drosophila. Null mutations in dAP-2, the sole AP-2 gene in Drosophila, cause severe leg shortening, loss of tarsal joints, and defects in proboscis, antenna, and central nervous system development. Drosophila is an excellent model system for genetic and bioinformatic analysis of regulatory gene networks within which AP-2 transcription factors function in developing tissues. This doctoral thesis describes research I have carried out using molecular genetic, transgenic, and comparative genomics approaches to identify cis-elements in dAP-2 that mediate its expression in developing leg and antenna (i.e., leg and antennal imaginal discs) of Drosophila. Previous studies showed that dAP-2 is expressed along the proximodistal (PD) axis of the developing leg in a segmental pattern representing future leg joints, and that dAP-2 expression in presumptive tarsal joints (4 distal-most joints) was dependent on Notch signaling. I have extended these findings by showing that dAP-2 is expressed in leg and antennal discs in nine and eight PD-axis domains, respectively; and that, in both disc types, the four distal-most dAP-2 expression domains require Notch signaling, while the remaining more proximal domains do not. I have identified two enhancers on dAP-2 genomic fragments BXE and E6 that activate reporter gene expression in distal (BXE) or proximal regions (E6) of leg and antennal discs in patterns coincident with endogenous dAP-2 expression. Both enhancers function preferentially with the dAP-2 exon 1a promoter. BXE contains multiple sub-fragments that act synergistically to mediate Notch-dependent activation and positive autoregulation by dAP-2 itself. Two essential binding sites for Suppressor of Hairless (Su(H), the transcription factor which transduces target gene effects of Notch signaling) and one essential binding site for dAP-2 were identified by phylogenetic footprinting, electrophoresis ... |
