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Abstract

Genetic studies on functional redundancy between profilin1 and profilin2 in mice and the role of the profilin ligand Mena in neuronal cell function and mouse behavior Profilin1 and profilin2 are two actin-binding proteins. Biochemically, proflin1 and profilin2 are similar in respect to their interactions with actin, phosphatidylinositol-4,5-bisphosphate (PIP2), and proteins containing poly-L-proline rich motives among which the Ena/VASP protein family members such as Mena. While profilin1 is highly expressed throughout development and adulthood in most tissues including brain, profilin2 is the neuronal specific isoform. Lack of profilin1 results in early embryonic lethality, while profilin2 KO mice are viable and show behavioral abnormalities. In this thesis I aimed to address three major questions: 1.Is there functional redundancy between profilin1 and profilin2 in vivo? 2.What is the role of the profilin ligand Mena in neuronal cell function and mouse behavior? 3.Is there a common functional pathway for profilin2 and Mena? In order to address functional redundancy between profilin1 and 2 I generated two different knock-in mouse lines in which profilin1 was substituted by mouse profilin2. However, for unknown reasons expression of profilin2 from the transgene was not detectable in tissues isolated from mice targeted with both knock-in strategies. My studies on Mena KO mice suggested an involvement of this protein in re-organization of the actin cytoskeleton and axon path-finding. In hippocampal neurons isolated from Mena KO mice, I showed that Mena is normally inhibiting the outgrowth of dendritic processes and cell spreading. In the mutant animals these alterations lead to axonal path-finding defects and behavioral abnormalities. My behavioral analysis showed that lack of Mena leads to impairment of locomotor activity, motor coordination and balance as well as to alteration in stress response. The severity of the phenotype was found to be age-dependent. Since Mena and profilin2 are known to interact in vitro I tried to investigate if both proteins act in common physiological pathways. Therefore, I compared the neuronal cell phenotype and the behavior of Mena KO and profilin2 KO mice. Interestingly, the morphological alterations are very similar in hippocampal neurons from Mena KO and profilin2 KO mice (longer primary processes and faster spreading). In terms of behavior, both KO lines showed alterations in locomotor activity, impairments in motor coordination and balance as well as altered stress response. The overlap and the differences of phenotypes suggest that profilin2 and Mena are linked in common functional pathways, but also that Mena and profilin2 have unique functions in mouse brain physiology.