, 2009), these lines do not fully recapitulate endogenous expression and show ectopic Cre recombination. We generated both Dlx1-CreER and Dlx5-CreER knockin drivers, which permit Dlx1+ and Dlx5+ interneurons to be identified and manipulated throughout development. As Dlx1 and Dlx5 are expressed predominantly in the SVZ in putative committed precursors at mid-gestation (i.e., becoming postmitotic after a limited number buy BIBW2992 of cell division) ( Eisenstat et al., 1999), CreER induction around this time (e.g., at E12) likely labels cohorts of GABA neurons with similar birth dates. Our initial characterization with E12 induction suggests that Dlx1 and Dlx5 may be expressed
in at least partially nonoverlapping
populations of progenitors. During tangential migration at E13, both the E12-induced Dlx1 and Dlx5 cohorts appeared to take similar routes, via the subventricular zone, into the cortex ( Figures 3A and 3B). By E15, however, the two cohorts showed very different patterns of migration. Whereas the Dlx1 cohort migrated throughout the marginal zone (MZ), cortical plate (CP), and intermediate zone (IZ), the Dlx5 cohort migrated predominantly in MZ ( Figure 3C-F). In mature cortex (P21), both cohorts settled in deep cortical layers despite their different migration routes, with a larger fraction of Dlx5-CreER-labeled neurons situated deeper in layer 6 than Dlx1-CreER-labeled neurons ( Figures 3G–3I). At later embryonic stages (e.g., E15), induction in Dlx1- and Dlx5- drivers gave rise to a very different pattern in the mature cortex buy C59 wnt (P21, Figures 3J and 3K). The Dlx1 driver mainly labeled upper layer interneurons. Many of these interneurons showed bipolar morphology and were reminiscent of CGE-derived populations such as VIP or CR positive interneurons. On the other hand, the Dlx5 driver labeled broader populations in all layers, suggesting that induction occurred not only in SVZ GBA3 progenitors but
also in migrating cells that had earlier become postmitotic. This distinction between the Dlx1- and Dlx5- drivers became more evident with adult induction ( Figures 3L and 3M), indicating that in the mature cortex Dlx1 expression is increasingly restricted to a small subset of interneurons, whereas Dlx5 expression is increasingly more ubiquitous among GABAergic neurons. Together, our initial characterization of these two driver lines demonstrated that Dlx1 and Dlx5 are differentially expressed in progenitors and developing interneurons at different developmental stages and thus may play different roles in GABAergic circuit development and function. In mammals, GABA is synthesized by two isoforms of glutamic acid decarboxylases GAD67 and GAD65, encoded by the Gad1 and Gad2 genes, respectively, and coexpressed in most brain regions ( Soghomonian and Martin, 1998).