Summary of Lhx9 andLhx2 expression patterns in the context of the neuromeric model (A) and schematic representation of Lhx combinatorial expression in the developing brain (B). Adapted from Puelles and Rubenstein (1993).A, Schematic E13.5 brain shows similarities, differences, and boundaries of expression of Lhx9(yellow) and Lhx2(dotted). Expression in the ventral mesencephalon and metencephalon is not indicated because of its rather “nuclear-like” pattern. B, Compilation of expression data forLhx1/5 (red; Sheng et al., 1997), Lhx2/9 (blue; this paper),Lhx3/4 (pink; Li et al., 1994;Bach et al., 1995), and Lhx6/7/8(green; Matsumoto et al., 1996; Grigoriou et al., 1998) on a “flattened brain” adapted from Bulfone et al. (1993). Gene expression is indicated by color-coded numbers, and a possible Lhx combinatorial code clearly emerges. The anteroposterior extension of expression is recapitulated byarrows at the bottom. Basal plate expression is not indicated. The zli is indicated by a dotted line. p1–p6, Prosomeres 1–6. See Table 1 for anatomical abbreviations.