A Mammalian Conserved Element Derived from SINE Displays Enhancer Properties Recapitulating Satb2 Expression in Early-Born Callosal Projection Neurons
Figure 5
AS021 activity and Satb2 expression decrease within deep layers at postnatal stages.
(A–B″) Immunostaining for Satb2 (red) and βgal (green) in coronal sections of P0 AS021-lacZ brains. The cortical plate was divided into 10 equivalent bins, with bin 1 corresponding to the deepest layer and bin 10 corresponding to the most superficial layer. (C-C″) High magnification of boxed region in B showing that only a fraction of Satb2+ neurons located in bin 6–7 (corresponding to more superficial layers) also express βgal (white arrowheads). Black arrowheads correspond to Satb2+ neurons that do not express βgal. (D) Quantification of the percentage of Satb2+ neurons co-expressing βgal (βgal+) within the 10 bins. (E–G″′) Immunostaining for Satb2 (red), Ctip2 (blue), and βgal (green) in coronal sections of P2 AS021-lacZ brains reveals a strong decrease of Satb2 staining specifically in deep layers. A similar decrease is observed for βgal, confirming the specificity of the AS021 activity. At both P0 and P2, AS021 activity remains specific to Satb2+ neurons (≥90%) in deep layers (D, H). Almost no co-labeling for βgal and Satb2 is observed in bins 8–10, corresponding to prospective layers 2–3 (superficial layers). A fraction of βgal+ neurons that expresses Satb2 also express Ctip2 (white arrowheads in G–G″′) in layers 5 and 6. Black arrowheads indicate βgal+ neurons that express Satb2 but not Ctip2 in layer 6. For each bin, 10–200 βgal+ cells were counted and 200–500 Satb2+ cells were counted in at least two animals for each stage. Graphs show mean ± SEM. Scale bars: 200 µm (A), 100 µm (B).