Determining the differential roles of the dock family of GEFs in drosophila development

Title from PDF of title page, viewed on May 29, 2015Dissertation advisor: Erika R. GeisbrechtVitaIncludes bibliographic references (pages 77-82)Thesis (Ph.D.)--School of Biological Sciences. University of Missouri--Kansas City, 2014The evolutionarily conserved Dock proteins function as unconventional guanine nucleotide exchange factors (GEFs). Upon binding to ELMO (Engulfment and cell motility) proteins, Dock-ELMO complexes activate the Rho family of small GTPases to mediate a diverse array of biological processes, including cell motility, apoptotic cell clearance, and axon guidance. Overlapping expression patterns and functional redundancy among the eleven vertebrate Dock family members, which are subdivided into four families (Dock-A, B, C, and D), complicate genetic analysis. Drosophila melanogaster is an excellent genetic model organism to understand Dock protein function as its genome encodes one ortholog per subfamily: Myoblast city (Mbc; Dock- A) and Sponge (Spg; Dock-B). The target GTPase of the Dock-A subfamily is Rac, which modulates actin dynamics. However, the in vivo GTPase downstream of the Dock- B subfamily remains unclear. Herein we show that the roles of Spg and Mbc are not redundant in the Drosophila somatic muscle, central nervous system (CNS), or the dorsal vessel (dv). Moreover, we confirm the in vivo role of Mbc upstream of Rac and provide evidence that Spg functions in concert with Rap1 to regulate aspects of adhesion. Together these data show that Mbc and Spg can have differential downstream GTPase targets. Our findings predict that the ability to regulate downstream GTPases is dependent on cellular context and allows for the fine-tuning of actin cytoskeletal or cell adhesion events in biological processes that undergo cell morphogenesis.Introduction -- The dock protein sponge binds elmo and functions in drosophila embryonic development -- Differential roles of the unconventional dock family members myoblast city and sponge in drosophila development -- Material and methods -- Discussio

The DOCK Protein Sponge Binds to ELMO and Functions in Drosophila Embryonic CNS Development

Cell morphogenesis, which requires rearrangement of the actin cytoskeleton, is essential to coordinate the development of tissues such as the musculature and nervous system during normal embryonic development. One class of signaling proteins that regulate actin cytoskeletal rearrangement is the evolutionarily conserved CDM (C. elegans Ced-5, human DOCK180, Drosophila Myoblast city, or Mbc) family of proteins, which function as unconventional guanine nucleotide exchange factors for the small GTPase Rac. This CDM-Rac protein complex is sufficient for Rac activation, but is enhanced upon the association of CDM proteins with the ELMO/Ced-12 family of proteins. We identified and characterized the role of Drosophila Sponge (Spg), the vertebrate DOCK3/DOCK4 counterpart as an ELMO-interacting protein. Our analysis shows Spg mRNA and protein is expressed in the visceral musculature and developing nervous system, suggesting a role for Spg in later embryogenesis. As maternal null mutants of spg die early in development, we utilized genetic interaction analysis to uncover the role of Spg in central nervous system (CNS) development. Consistent with its role in ELMO-dependent pathways, we found genetic interactions with spg and elmo mutants exhibited aberrant axonal defects. In addition, our data suggests Ncad may be responsible for recruiting Spg to the membrane, possibly in CNS development. Our findings not only characterize the role of a new DOCK family member, but help to further understand the role of signaling downstream of N-cadherin in neuronal development