Abstract
Background information PIX proteins are exchange factors for Rac and Cdc42 GTPases that are differentially expressed in the brain, where they are implicated in neuronal morphogenesis. The PIX family includes the two members aPIX and beta PIX, and the gene of aPIX is mutated in patients with intellectual disability. Results We have analysed the expression of PIX proteins in the developing brain and addressed their role during early hippocampal neuron development. Mass spectrometry identified several beta PIX isoforms and a major p75 aPIX isoform in brain and hippocampal cultures. PIX proteins expression increased with time during neuronal differentiation in vitro. The PIX partners GIT1 and GIT2 are also found in brain and their expression was increased during neuronal differentiation. We found that aPIX, but not beta PIX, was required for proper hippocampal neuron differentiation, since silencing of aPIX specifically hampered dendritogenesis and axonal branching. Interestingly, the depletion of GIT2 but not GIT1 mimicked the phenotype observed after aPIX knock-down. Over-expression of aPIX specifically enhanced dendritic branching, while both aPIX and beta PIX over-expression affected axonal morphology. Again, only over-expression of GIT2, but not GIT1, affected neuritic morphology. Conclusions The results indicate that aPIX and GIT2 are required for neuronal differentiation, and suggest that they are part of the same pathway, while GIT1 and beta PIX are dispensable for early hippocampal neurons development.