Uncovering the molecular basis of SEPT2-associated Tyshchenko syndrome

点击翻译按钮获取中文摘要

Tyshchenko syndrome (TS) was first described in 2011 by Tyshchenko et al. as an autosomal-dominant syndrome presenting with distinct facial features, specific malformations and learning disabilities. The minor anomalies resemble Baraitser-Winter Cerebrofrontofacial syndrome (BWCFF). Whereas mutations in either non-muscular Actin gene ACTB or ACTG1 are known to cause BWCFF, no underlying cause of TS could be found.Via whole exome sequencing, we identified a missense mutation in SEPT2 in one of the two original families described by Tyshchenko et al. In addition, in two other unrelated patients with the same striking facial features we found de novo missense mutations in SEPT2. In a 3-D protein model of human Septin 2, all three mutations are located in close spatial proximity.Septin 2, like other Septins, plays a major role in a variety of cell processes including cytokinesis. Septins are important components of the cytoskeleton and serve as scaffolds and diffusion barriers in the cell. They all possess a guanine nucleotide binding domain with GTPase activity and an NC interface, that is their N- and C-terminal extensions. Via both domains, Septins interact forming linear hetero-oligomers, most commonly with Septin 2 located is its centre, functioning as an initiator of the complex formation. Amongst others, filamentous Septins also closely co-localize with Actin and control F-Actin assembly and Actin organization.The main goal of this project is to delineate the molecular mechanisms leading to SEPT2-related TS and to unravel the molecular mechanisms in Septin-Actin interaction, that lead to a similar yet differing clinical presentation of TS and BWCFF.To do so, we will perform in vitro experiments to demonstrate the effect of SEPT2 mutations on Septin-oligomerization using immunoprecipitation of recombinant proteins and protein-domains. As all of the mutations found in TS patients in Septin 2 are located in the NC interface, we hypothesize that the homodimerization of Sept2 or the hetero-oligomerization with other Septins might be disturbed in TS patients. In addition, we will investigate the effects of SEPT2 mutations on the Septin function during cytokinesis. We will also measure Septin-Actin interactions via immunostaining and using purified recombinant proteins in order to establish a functional link between TS and BWCFF. Eventually, we want to deepen our insights into the interaction between different cytoskeletal components and broaden our knowledge of the formation and function of the cytoskeleton. Through this, we want to lead to an ultimate benefit to the patients, understand their condition, anticipate future complications and facilitate the development of therapeutic possibilities.