Resumo

Radial glia (RG) cells are the major cerebral cortex stem cell population, that originates neurons and glial cells. The mechanisms underlying RG maintenance or its differentiation into specific cell types are not completely known. We previously demonstrated that transforming growth factor beta 1 (TGF-beta1) promotes astrocyte generation from RG cells in vitro. Here, we investigated the role of TGF-beta1 in RG-astrocyte transformation in vivo. To address this question, 14 day-pregnant swiss mice (E14) were subjected to in utero intraventricular injection of TGF-beta1 (100ng) followed by intraperitoneal injections of BrdU. After 48 hours, the embryos were removed, the brains fixed and processed for immunohistochemistry for nestin (RG marker), GFAP (astrocyte marker), BrdU (proliferation marker) and ErbB2 (neuregulin receptor expressed in RG). TGF-beta1 induced changes in nestin+ cell morphology characterized by loss of polarity mainly in the dorsal cortex (DC), and in less extension in the lateral cortex (LC). This event was followed by disruption of basal membrane on pial surface, characterized by ectopic laminin+ cells. We also observed a 1,2 fold increase in the number of GFAP+ cells specifically in DC, whereas no change was shown in LC. This event was followed by a decrease in ErbB2 labeling intensity in DC only. Additionally, TGF-beta1 completely impaired formation of DC cortical plate and decreased by 1,5 fold the number of BrdU+ cells in LC cortical plate, suggesting deficits in neuronal generation and/or migration. In vitro assays using RG cell cultures isolated from E13 neurospheres further supported in vivo gliogenic action of TGF-beta1 (4,5 fold increase in the number of GFAP+ cells in vitro). Together, these data suggest that TGF-beta1 is a potential modulator of RG-astrocyte transformation and suggest that it plays a key function in the organizing ErbB2 cellular distribution, essential for RG stem cell phenotype maintenance in the cerebral cortex.