, 1995). Using the same antibody as in the present study, we showed that p-cofilin immunolabelling selleck kinase inhibitor is strongest

in the marginal zone and in the leading processes of migrating neurons approaching the cortical surface (Chai et al., 2009). We hypothesized that it is this Reelin-induced stabilization of the cytoskeleton in these processes that anchors them to the marginal zone, thereby determining the vertical orientation of radially migrating cortical pyramidal cells. Similar to Reelin’s proposed function on the migration of SPNs, Reelin in the neocortical marginal zone is likely to act as a stop signal, preventing migrating neocortical neurons from invading the marginal zone. In contrast, in the reeler mutant, the marginal zone is densely populated by neuronal cell bodies. We have reason to assume that the simultaneous presence of Reelin and p-cofilin is causally related: not only is the amount of p-cofilin

dramatically reduced in tissue from reeler mutants, apoer2 mutants and dab1 mutants (Chai et al., 2009), but incubation of reeler tissue in the presence of recombinant Reelin strongly increased cofilin phosphorylation, an effect that was confirmed for spinal cord tissue in the present experiments. Moreover, incubation of reeler tissue in the presence of recombinant Reelin strongly increased the phosphorylation of LIM kinase 1 (LIMK1), the enzyme that phosphorylates cofilin. LIMK1 phosphorylation and cofilin phosphorylation were significantly decreased when the tissue was incubated in the presence of PP2, an inhibitor of Src family PAK6 kinases that phosphorylate Dab1 upon see more Reelin binding to its receptors (Chai et al., 2009). Finally, the Reelin-induced phosphorylation of cofilin was significantly decreased when blockers of phosphatidylinositol-3 kinase were added. Taken together, our previous studies on neocortical tissue as well as the present experiments on tissue from the spinal cord provide strong evidence for the Reelin signalling cascade being involved in the phosphorylation of cofilin and hence cytoskeletal stabilization.

The resulting effect is similar in the cerebral cortex and spinal cord: migratory arrest of late generated neurons destined for superficial layers in the neocortex and of SPNs destined for the IMLC of the spinal cord. Compatible with this concept is that strongest Reelin expression in the spinal cord is found during the period when SPNs assemble in the IMLC (around E13; see Fig. 4). The large extracellular matrix protein Reelin plays an important role in the ordered lamination of cortical and cerebellar structures and in the assembly of SPNs in the spinal cord. One crucial mechanism that is induced by the Reelin signalling cascade is the phosphorylation of cofilin, which stabilizes the cytoskeleton and counteracts cell motility.