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Fig. 6 N1ICD expression and cell proliferation during central nervous system development. A-P: N1ICD expression (A,E,F,G,I-K,M-O), in situ hybridization (B,C), bromodeoxyuridine (BrdU) staining (D,H,L,P). A: At embryonic day (E) 9.5, N1ICD stains preferentially hindbrain cells in the abluminal region (arrow), and to a lesser extent those closest to the neural canal lumen (arrowhead). B,C: Delta1 (B) transcription is predominant in the dorsal region (arrow) and Jag1 (C) is transcribed in two stripes (arrows) on either side of the midline. D: At E9.5, BrdU staining in hindbrain is predominant in the abluminal region (arrow). E: An E10.5 embryo sectioned at the forebrain (fb) level. N1ICD staining is widespread in the neuroepithelium, except in the optic stalk (os, arrowhead). F: Detail showing N1ICD expression (arrow) in forebrain. G: In the hindbrain region, N1ICD is expressed in the neuroepithelium (arrow in inset) and is excluded from the cells closer to the lumen (arrowhead). H: BrdU staining in the hindbrain is relatively similar to N1ICD expression. I: General view at E11.5 of the forebrain region with telencephalic vesicles (tc; *) and diencephalon (dc). J: Detail of one vesicle. Note predominant N1ICD expression in nuclei closer to the ventricular zone (arrow) and its exclusion from the distal region (arrowhead). K: N1ICD expression in ependymal layer (arrow) of the spinal cord and condensing dorsal root ganglia (drg). No expression is detected in postmitotic ventral horn (vh) cells (arrowhead). L: BrdU staining at E11.5 reveals a pattern similar to that of N1ICD. M: General view of diencephalon at E13.5. N: Detail showing N1ICD staining in neuroepithelial cells closer to the neural canal (arrow), while distal cells are negative (arrowhead). O,P: In the spinal cord, N1ICD expression is restricted to the ventricular zone (arrow in O) in a pattern similar to BrdU staining (P). All are transverse sections. Scale bars = 300 μm in A-D, 500 μm in E-H,J-L,N-P, 0.8 mm in I; 1 mm in M.