Role of profilin1 in neocortical development and gyrification

• Applicants: Professorin Silvia Cappello, Ph.D.; Professor Dr. Marco Rust
• Subject Area: Developmental Neurobiology ; Molecular Biology and Physiology of Neurons and Glial Cells
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 391970916

Neocortical malformations are an important aspect in human brain disorders such as lissencephaly or heterotopia, and they can result from defects in cell proliferation, cell differentiation or neuron migration. Cytoskeletal dynamics are crucial for these processes, and human genetic studies or the analyses mutant mice, including studies from our groups, implicated cytoskeletal regulators in neocortical development. However, the mechanisms that control cytoskeletal dynamics during neocortex development are only poorly understood. We hypothesize that the cytoskeletal regulator profilin1 is crucial for cell fate control of neural stem cells and neocortex development. Our hypothesis is based on our preliminary data on brain-specific profilin1 knockout mice that revealed a strongly increased number of proliferating cells in the subventricular/intermediate zone and an elevated number of basal progenitors including Pax6-positive basal radial glia at embryonic day 14. These changes were associated with the occurrence of folds that we frequently found in the neocortex of all investigated mutants. The abundance of basal radial glia in the developing neocortex is a major difference between lissencephalic (e.g. mouse) and gyrencephalic brains (e.g. human). According to the 'radial cone hypothesis' it has been postulated that basal radial glia provide additional radial subunits that are required to increase the pial surface relative to the ventricular surface and to ultimately promote neocortical folding in gyrencephalic brains. Since we found elevated numbers of basal radial glia and folds in profilin1 knockout mice, we hypothesize that our mutants are a valuable model to study the process of gyrification and to strengthen the radial cone hypothesis. In a multidisciplinary approach, by combining mouse genetics with in utero electroporation-mediated gene transfer into single cells and state of the art cell biological and microscopic approaches, the proposed project is designed to i) comprehensively characterize the function of profilin1 during mouse neocortex development, from molecular mechanisms to its systemic significance, and ii) test whether some rudimentary gyrification can occur in a lissencephalic brain upon inactivation of profilin1. Moreover, in a translational approach, by CRISPR/Cas9-mediated gene editing in cerebral organoids derived from human induced pluripotent stem cells, we finally want to connect our findings in mice with human neocortex formation to test whether profilin1 has acquired specific functions among lissencephalic and gyrencephalic species or whether profilin1 dysfunction is associated with neocortical malformation in humans, similar to mice.

• DFG Programme: Research Grants