Embryonic expression of her8a. Expression is revealed by whole-mount in situ hybridization at the stages indicated (som: somites, hpf: hours post-fertilization) together with other positional marker genes (B,C,E, color-coded) or proteins (G, immunocytochemistry for the neuronal marker HuC/D in green). A-E and H are dorsal views of flat-mounted embryos, F,I are lateral views, all embryos are viewed anterior left. G is a cross section of a 24hpf embryo at midbrain levels (as indicated in F). At early neural plate stages, the domain of strongest her8a expression covers the mid- and anterior hindbrain (bracket in A-C). It overlaps the presumptive midbrain-hindbrain boundary (her5-positive, purple arrow in C) and the progenitor pools separating medial and lateral hindbrain neurons (her3-positive, purple arrow in B). It extends into rhombomere 2 (white arrowhead in C), more posterior rhombomeres being more weakly labeled. At 10 somites, expression in the midbrain is maintained. It resolves in stripes in the rhombencephalon (D,E). It avoids the midbrain-hindbrain boundary and zona limitans intrathalamica (asterisk). From 24 hpf onwards, her8a characterizes the ventricular zone and progenitor domains of the neural tube (G-I, arrows in I point to the ventricular zone and the arrowhead points to the progenitor domain of the optic tectum). Abbreviations: e: eye field, mid: presumptive midbrain, mhb: midbrain-hindbrain boundary, r: rhombomere. Scale bars: 100 μm.