Reference : PhD Juliette Godin
The protein Kif21B is a relatively poorly studied member of the kinesin superfamily. Kinesin motor proteins play a fundamental role for normal neuronal development by controlling intracellular cargo transport and microtubule cytoskeleton organization in both axons and dendrites. Regulating kinesin activity is essential to ensure their proper functioning. Importantly, kinesin misregulation often leads to severe human neurodevelopmental disorders, suggesting a key role of the kinesin superfamily in brain development. Kif21B is essential for brain morphology in mice. Indeed, Kif21B knockout mice display severe brain malformation including microcephaly, hydrocephaly and disgenesis of the corpus callosum. Moreover, we recently identified several mutations in Kif21B gene in patients with corpus callosum defects, intellectual disabilities and other clinical features such as microcephaly or facial dimorphism. The identification of those mutations strongly supports of role for Kif21B in neurodevelopment. However functional characterization of the variants is still needed to understand how disruption of Kif21B can lead to substantial neurodevelopmental defects.
In this project, we will focus on the brain connectivity defects. We therefore aim at understating how Kif21B regulates brain connectivity in vivo. We will analyse axonal growth and branching of callosal neurons in vivo using in utero electroporation of CRE-expressing plasmid in Kif21Blox/lox embryos and evaluate
1) the connectivity at the midline;
2) the axonal branching in the contralateral side and
3) the ipsilateral microcircuitry.
In parallel, we will analyze the commissural fibers in Kif21B KO brains using
1) diffusion tensor imaging at P60;
2) commissural and axonal markers at different development stages and
3) anterograde DiI tracing. Those in vivo analysis will be complemented by in vitro investigations of axonal length and branching in primary culture of cortical neurons isolated wild-type and KO embryos. We will also monitor axonal growth and growth cone dynamic by time lapse imaging (DIC). Our ultimate goal is to understand by which mechanisms Kif21B regulates axonal development and growth.
To this end, we will perform complementation experiments with wild-type and truncated version of Kif21B, lacking key functional domains. As intracellular transport is a key determinant of axonal growth, we expect a crucial role of KIf21B processivity function in the regulation of brain connectivity. If so, we will determine the cargoes that may be involved in that process. Altogether, we believe that further characterization of molecular function/dysfunction of Kif21B and its variants in axonal extension and branching should bring new light on the function of kinesins in the developing brain.
Application Deadline : Nov. 1, 2018