Figure 4. Conditional deletion of Cyp26b1 using Synaptotagmin6-Cre (Syt6-Cre). A–E, Recombination in Syt6-Cre transgene mice. A–E, Expression of ZSGreen in Syt6-Cre/+; Ai6 (ZSGreen Cre reporter) mice at E12.5 (A), E14.5 (B), and P0 (C–E) are shown. All sections are coronal, and the midline is to the left. At E12.5, the expression of ZSGreen reporter is found in meninges (A, arrow) and preplate (A, arrowhead), but not in the rest of the cortex or MGE and LGE. At E14.5, a small number of cortical cells (B, double arrows) below the marginal zone (B, arrowhead) start to express ZSGreen. C–E, At P0, many layer 6 cells of frontal cortex express ZSGreen (C, arrow), but not in more caudal neocortex (D, Ncx), CA1, CA3, and hilus regions of the hippocampus (E, note that strong signal is found in the meninges of the hippocampus) or the amygdala (F, Amy). ic, Internal capsule. Scale bar, 200 μm. F–Q, Generation of conditional Cyp26b1 knock-out mice. F–Q, In situ hybridization of frontal sections of P8 (F, G, I, J, L–Q) or P14 (H, K) Cyp26b1 conditional knock-out (I–K, O–Q) and control littermate (F–H, L–N) brains. Cyp26b1 was conditionally knocked out using the Syt6-Cre transgene. Syt6 is expressed in layer 6 of both control (F) and Cyp26b1 knock-out (I) brains (arrow). The expression of Cyp26b1 in layer 6 of frontal cortex (arrow) is detected in control brains, but not in Cyp26b1 knock-out brains at P8 (G, J) and P14 (H, K). The expression of Cyp26b1 in agranular insula is unchanged in Cyp26b1 knockouts (G, H, J, K, arrowhead). The expression of Cyp26b1 in CA3 and hilus region of the hippocampus (L, O, arrowhead), globus pallidus (M, P, arrow), and amygdala (N, Q, arrowhead) is unchanged in Cyp26b1 knockouts. Scale bar, 1 mm.