Fig. 1. Identification of a somite-specific Epha4 enhancer. (A) The lacZ transgene constructs used to identify the cis-acting somite enhancer within the Epha4 genomic region. The numbers of transgenic mouse embryos that expressed ß-gal in the somites, among the transgene-positive embryos, are indicated on the right. E, EcoRI; H, HindIII; N, NheI; Sa, SacI; Sw, SwaI; P, PmaCI; X, XbaI. (B,C) Lateral view of ß-gal activity driven by the 630 bp (HindIII) Epha4 enhancer fragment in a 10.5 dpc embryo. A magnified image in the somitic region of B is shown in C. (D,E) Comparison by in situ hybridization at 10.5 dpc of the transgene expression (lacZ) in a transgenic embryo (D) with endogenous Epha4 expression in the wild-type embryo (E). In situ signals in the anterior PSM are indicated by arrows in the lower panels showing magnified images. (F,G) ß-Gal activity driven by the 630 bp enhancer in 10.5 dpc wild-type (F) and Mesp2^L/L embryos (G).