Figure 7.

Dmrt5 regulates the timing of the earliest Ctip2+ cortical neuron generation. (A) To compare the birthdate of Ctip2 immunoreactive cohorts of cortical neurons in WT and Dmrt5^−/−, BrdU was injected at E11.5, E12.5, or E15.5, and brains were harvested at E18.5. Coronal sections from these birth dated WT and Dmrt5^−/− brains were immunostained for Ctip2 and BrdU. The percentage of Ctip2⁺, BrdU⁺, and co-labeled cells was analyzed (n = 3, 3, and 3 brains for the three stages; at least three sections of each brain). Examples for co-labeled cells are marked with white arrowheads. Labeled-BrdU nuclei were counted in rectangular fields of 450 μm in width extending from the VZ to the pial surface through the neocortex of WT or Dmrt5^−/− brains. Prevalence of early-born Ctip2 immunoreactive cells was quantified in WT and Dmrt5^−/− brains. (B) Quantification of colocalization of the BrdU-labeled cells with Ctip2 among the BrdU⁺ population and (C) among the Ctip2⁺ population on at least three sections of each stage injected brains (n = 3, 3, and 3). ^*P < 0.05 (unpaired Student’s t-test). Data are given as mean ± SD. There was no significant difference in the numbers of Ctip2⁺ cells in the BrdU+ cohorts labeled at E11.5, E12.5, and E15.5 and examined at E18.5, but there was a significant increase of the proportion of Ctip2⁺ neurons in the cohort of cells labeled by a BrdU pulse at E11.5 but not at E12.5 or E15.5. Scale bars represent 50 μm.