In contrast, we found that MGE-derived cells obtained from IN-Cxcr7

mutants fail to respond to Cxcl12 ( Figures 5D–5F). Thus, Cxcr7 is necessary for the chemotaxis of cortical interneurons in response to Cxcl12. The previous results were unexpected, since most MGE-derived cells express both Cxcr4 and Cxcr7 receptors (Figure 2) and Cxcr4 mediates the Cxcl12-dependent migration of these neurons (Li et al., 2008, López-Bendito et al., 2008, Stumm et al., 2003 and Tiveron et al., 2006). A possible explanation might be that both chemokine receptors cooperate in migrating interneurons and that one receptor alone is not sufficient to elicit a response to Cxcl12. Alternatively, Cxcr7 might be required for normal Cxcr4 function. To distinguish

between both possibilities, we examined whether Cxcr4 signaling was impaired in the absence of Cxcr7. To this end, Selleckchem BMS-387032 we prepared cultures from the ventral telencephalon of control and Cxcr7 mutant embryos, and stimulated them with recombinant Cxcl12. As expected from previous reports on Cxcr4 signaling ( Li and Ransohoff, 2008), stimulation with Cxcl12 strongly promoted the phosphorylation of the extracellular signal-regulated kinases 1 and 2 (Erk1/2) in control cells ( Figures 5G and 5H). In contrast, Cxcl12 stimulation failed to elicit phosphorylation of Erk1/2 in cells obtained from Cxcr7 mutants ( Figures 5G and 5H). The previous experiments reinforced SP600125 clinical trial the hypothesis that Cxcr4 function is compromised in the absence of Cxcr7. One possible mechanism could be that Cxcr7 is required for normal Cxcr4 expression. To test this idea, Cell press we analyzed the distribution of Cxcr4-expressing cells in the cortex of control and IN-Cxcr7 mutant embryos. We found that Cxcr4 mRNA is normally expressed in the absence of Cxcr7. However, as predicted from the MGE coculture experiments, Cxcr4-expressing neurons were found to distribute abnormally in the cortex of IN-Cxcr7 mutant embryos ( Figures 6A and 6D). Indeed, the distribution of Cxcr4-expressing

cells closely resembled that observed for Lhx6-expressing cells in IN-Cxcr7 mutant embryos. We next wondered whether the levels of Cxcr4 protein were normal in Cxcr7 mutant interneurons. We found that Cxcr4 immunoreactivity was reduced in the subpallium of Cxcr7 mutant embryos compared with controls ( Figures 6B and 6E). Most strikingly, Cxcr4 immunoreactivity was almost entirely absent from the cortex of IN-Cxcr7 mutant embryos ( Figures 6B, 6B′, 6E, and 6E′). These defects were also obvious in Cxcr7 null mutants ( Figures S2A–S2D). Because the antibody used to detect Cxcr4 in these experiments does not recognize the activated, phosphorylated form of Cxcr4 ( Figures S2E and S2F), these results indicate that either all Cxcr4 present in Cxcr7-deficient interneurons has been phosphorylated, or that Cxcr4 is indeed absent from these cells.