Fig. 3. Spatial gene expression across the field of neocortical progenitor cells is in gradients, rather than discrete domains. (A) Expression of rostrally enriched transcripts in neocortical progenitor cells at E11.5 and E13.5. In situ hybridisation on 14-µm parasagittal sections at each age. Rostrocaudal orientation and gene identifiers are as indicated. (B) Expression of caudally enriched transcripts at E11.5 and E13.5. (C) Expression of genes predicted from array analyses as temporally regulated and correlating with the neurogenetic gradient. Both genes are expressed rostrally initially (E11.5) and subsequently (E13.5) expression spreads caudally. (D) Whole-mount in situ hybridisation for caudally enriched transcripts. With the exception of the EphA3 whole-mount, which was carried out at E12, the embryos are all E11.5. Genes are as labelled in each panel. Arrow indicates rostral forebrain expression. Scale bars: 0.5 mm.