An investigation into the relationship between a putative tumour suppressor and a cell shape regulator in the fruit fly
The process of morphogenesis during development involves complex, co ordinated changes in cell shape and cell movement. The molecular mechanisms underlying this fundamental aspect of development remain to be fully elucidated, although some key aspects have been characterised. Drosophila Rho Guanine nucleotide Exchange Factor 2 (DRhoGEF2) is required during morphogenesis for control of cell shape. A novel interaction has recently been discovered between the DRhoGEF2 PDZ domain and the Drosophila orthologue of Mutated in Colorectal Cancer (MCC), a putative tumour suppressor gene. The interaction between MCC and a RhoGEF has not been previously documented in any organism. MCC may act as a block on the cell cycle, and this interaction could, therefore, represent a link between morphogenesis and cell division. This thesis explores the functional significance of MCC and in particular its putative contribution to morphogenesis through its interaction with DRhoGEF2. The observation of MCC expression in the Drosophila embryonic central nervous system suggests a functional role in nervous system development. Ectopic over-expression of MCC does not produce any obvious phenotype over controls. Furthermore, RNAi and P-element mutagenesis to knock out MCC expression do not yield a phenotype, and therefore do not indicate any clear function for MCC. The potential influence of MCC on the signals mediated by DRhoGEF2 therefore remains obscure and requires further investigation. Three potential targets for the DRhoGEF2 PDZ domain identified through a yeast 2-hybrid approach, including MCC, carry a proline-X-threonine-X-leucine motif at their C-terminus. Initial studies indicate that mutation of the proline, threonine and leucine residues at the C-terminus of MCC disrupts its binding to DRhoGEF2 PDZ domain. This work suggests further study to explore whether this C-terminal motif defines a group of DRhoGEF2-specific interacting proteins.