, 2001). Slits are the principal ligands for the Robo receptors ( Kidd et al., 1999), to which they bind in association with heparan sulfate proteoglycans ( Hu, 2001). There are three Slit genes in mammals, and all of them are expressed in developing CNS ( Marillat et al., 2001). Slits bind promiscuously to Robo receptors in vitro ( Brose et al., 1999; Li et al., 1999), which suggests that these proteins may cooperate in vivo in those locations in which their expression patterns overlap ( Bagri et al., 2002; Plump et al., 2002). The functions of Robo receptors have been classically studied in postmitotic

cells, most typically in neurons. However, Robo receptors also seem Selleck Osimertinib to be expressed in progenitor cells, at least in some regions of the developing brain (Marillat et al., 2001). A few studies have even hinted at a possible role for Robo receptors in neurogenesis (Andrews et al., 2008; Mehta and Bhat, 2001), but the precise mechanisms through which Slit signaling may control this process are unknown. In Drosophila, slit seems to modulate EGFR activity neurogenesis by promoting asymmetric terminal divisions in particular neural lineages ( Mehta and Bhat, 2001). Considering the highly conserved roles of Slits and their Robo receptors in evolution ( Brose and Tessier-Lavigne, 2000), it is conceivable that Slit/Robo signaling may play a similar role in the vertebrate

brain. Here we have tested the hypothesis that Slit/Robo signaling may contribute to regulate neurogenesis in the mammalian CNS. We focused most of our analysis in the developing cerebral cortex, for which the cellular mechanisms of neurogenesis are beginning to be elucidated Carnitine palmitoyltransferase II (Fietz and Huttner, 2011; Noctor

et al., 2007; Pontious et al., 2008). During early phases of neurogenesis, cortical progenitor cells residing in the ventricular zone (VZ) divide symmetrically to increase the pool of dividing cells. As neurogenesis progresses, VZ progenitors begin to divide asymmetrically to self-renew and produce new neurons or, more frequently, to generate IPCs. These progenitors, which localize to the subventricular zone (SVZ), will generate additional neurons after one or more rounds of divisions. This two-step process of neurogenesis is highly reminiscent to that observed during the development of the CNS in Drosophila ( Skeath and Thor, 2003), but the mechanisms controlling these dynamics remain poorly characterized. We found that progenitor cells throughout the entire mouse brain and spinal cord transiently express Robo1 and Robo2, in particular during early stages of neurogenesis. Analysis of Robo1 and Robo2 double (Robo1/2) mutants revealed that these receptors are required to maintain the proper balance between primary and intermediate progenitors, because loss of Robo signaling leads to a decrease in VZ progenitors and a concomitant increase in the number of IPCs.