The extra ciliary roles of Meckel-Gruber syndrome proteins
Thesis or dissertation
University of Exeter
Reason for embargo
It is intended that data from the present thesis be published in scientific journals, and this embargo period will protect sensitive data during this process.
Meckel-Gruber syndrome (MKS) is a recessive genetic disease that is uniformly lethal in affected children due to resultant developmental defects in the kidney and brain. 13 MKS genes have been identified, and further candidate genes have been linked to this disease, all encoding unrelated proteins. Their role is believed to be in generation and compartmentalisation of the primary cilium, a microtubule-based organelle that functions in signal transduction of developmentally-crucial pathways. However, recent evidence indicates that these proteins are also likely involved in regulation of the actin cytoskeleton. Furthermore, research is beginning to uncover roles of other ciliopathy proteins in regulation of additional subcellular structures, such as the microtubule cytoskeleton, focal adhesions and the Golgi. To begin to understand the roles of the MKS proteins beyond the cilium, I examined a number of cellular features of patient fibroblasts carrying mutations in TMEM216 (MKS2) and TMEM67 (MKS3). In this thesis, I describe the temporal appearance and nature of prominent actin bundles observed in these cells, and analyse the dependency of these on the Rho/ROCK signalling pathway. Furthermore, I identify novel alterations to the microtubule cytoskeleton and organisation of the Golgi complex in MKS patient cells, and subsequently establish a temporal order of these phenotypes, demonstrating microtubule defects as the first to occur in these cells. Finally, I connect these phenotypic defects to Rho/ROCK signalling. In contrast to the prevailing view in the ciliopathy field, I believe that a diffusion barrier at the transition zone is not the primary role of MKS proteins. Instead I propose, supported by these data, that MKS protein complexes play a dual role as effectors of Rho signalling in addition to performing a structural role with particular importance in tethering the cytoskeleton to membranes. I therefore conclude that these, and other ciliopathy protein complexes, may act as important signal transduction and structural components at multiple locations throughout the cell.
PhD in Biological Sciences