MOLECULAR AND GENETIC STUDIES OF TRANSCRIPTION FACTOR AP-2 IN DROSOPHILA APPENDAGE DEVELOPMENT

Open Access
Author:
Ahn, Younwook
Graduate Program:
Biochemistry, Microbiology, and Molecular Biology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
August 23, 2005
Committee Members:
  • Richard W Ordway, Committee Member
  • Robert Paulson, Committee Member
  • Pamela J Mitchell, Committee Chair
  • Wendy Hanna Rose, Committee Member
  • Graham Hugh Thomas, Committee Member
Keywords:
  • Hox proteins
  • transcriptional regulation
  • enhancers
  • gene expression
  • limb development
Abstract:
Transcription factor AP-2 has essential roles in nervous system, oro-facial and limb development based on studies of Drosophila and vertebrate model organisms. Previous studies have shown that dAP-2, the sole AP-2 family gene in Drosophila, is expressed in leg, antennal, and labial imaginal discs (anlaga of adult legs, antennae and proboscis, respectively) in multiple domains along the proximal-distal (PD) axis of the growing appendage. In leg imaginal discs of late larvae and early pupae, dAP-2 is expressed in nine domains of epithelial cells that presage boundaries (joints) between the ten segments comprising the adult leg. Genetic analysis has established that dAP-2 is required cell-autonomously for leg joint development and non-autonomously for outgrowth of leg segments. This thesis presents contributions I have made to broaden our understanding of molecular mechanisms regulating expression of dAP-2 in developing legs and antennae. I report the identification of multiple cis-regulatory elements each responsible for activation of particular domains of dAP-2 expression along the PD-axis of the leg and antenna. Molecular, genetic and biochemical analyses of one of these enhancers, PrF, which activates expression at the proximal end of the presumptive femur, reveals that it is directly regulated by Hox transcription factors and their homeodomain cofactor Extradenticle (Exd). Hox proteins, Exd, and Homothorax (Hth, a homeodomain protein required for nuclear localization of Exd) and their vertebrate orthologs have ancient roles in development of proximal regions of limbs. However, until this thesis, direct target genes for Hox and Exd proteins in leg development were unknown. Our analysis of dAP-2 transcriptional enhancers reveals that the seemingly simple repetitive pattern of dAP-2 expression in developing limbs is mediated by multiple separable enhancers each responsible for activation of a particular portion of the dAP-2 expression pattern and responding to region- and appendage-specific regulatory factors. Also described in the thesis are experiments using tissue-specific RNA interference (RNAi) to induce spatiotemporally restricted loss of dAP-2 and two other proteins, Nubbin, a POU-domain transcription factor implicated in limb development, and CG10440, a BTB/POZ protein reported to be a protein:protein interaction partner for dAP-2.