Resumo

Reelin is an extracellular matrix glycoprotein synthesized mainly by Cajal-Retzius neurons in the embryonic cerebral cortex marginal zone (MZ). The reeler mutant mouse presents a disruption of the inside-out layering of cerebral cortex by a migration defect. It has been proposed that reelin provides a stop signal for neurons that migrate radially from the VZ doted with the reelin receptors VLDL and APoER2 which promote the phosphorylation of adaptor protein Dab1 and with the involvement of α3β1 integrin. In our work we investigated a role for reelin as a regulator of GABAergic tangential migration. Part of the GABAergic neurons from medial ganglionic eminence (MGE) migrate to the cerebral cortex via a reelin rich pathway in the MZ. We studied the migratory response of MGE neurons to reelin as well as two other telecephalic regions, the cortical hem (CH) and the lateral olfactory tract region (LOT), both rich in reelin producing cells and GABAergic neurons. We have investigated the phenotype of GABAergic, reelin and calretinin positive neurons as to the expression of molecules of the reelin signaling pathway in migrating neurons from cultivated explants. We found that reelin positive cells do not express any of the reelin receptors or intracellular Dab1 in all the regions studied. However, GABAergic neurons from all regions expressed VLDLR, ApoER2, α3β1 integrin and Dab1. To address the role of reelin in GABAergic neuronal migration we used the transwell assay and studied the behavior of the pooled telencephalic regions to a medium conditioned by HEK293T transfected with full length reelin vector (MC-reelin) as compared to control medium conditioned by HEK293T (MC-HEK). We found that GABAergic cells migrate significantly more to the reelin containing compartment. Nestin positive cells and GABAergic neurons expressing nestin show an even more dramatic increase. We have also shown by the expression of Ki67 that cells significantly increased proliferation when in MC-reelin. When CR-50 antibody against reelin was used with MC-reelin the increase in migration was reverted, significantly decreasing the migration of total cells, GABAergic neurons, nestin positive cells or GABAergic-nestin cells showing that these effects are specific to reelin. We also studied the response to MC-reelin of CH, MGE and LOT cells separately. We found that MGE is doted with more migratory cells overall. However, its contingent of migratory GABAergic cells is not significantly larger than the other regions, however its response to MC-reelin was larger than LOT and CH in terms of GABAergic migration. We conclude that reelin provides an attraction signal for MGE, CH and LOT GABAergic migration and that reelin signaling also increase progenitor migration and proliferation in the developing telencephalon. Fomentos: PRONEX, FAPERJ, IBN-Net, CAPES-PROCAD, CNPq, UGF-SETI, FINEP.