Fig. 3. Characterisation of the head expression in pEEBZ transgenic embryos. (A) Reporter gene expression is seen in the head at 9.5 dpc. (B) In transverse sections (plane of section shown in A) strong expression is detected in the cephalic mesoderm together with a few stained cells in the brain (arrows). (C) Dissection of the head of a 12.5 dpc y200-Myf5-nlacZ embryo shows reporter expression in prosomere p1 and in the mamillary body as previously described (Tajbakhsh and Buckingham, 1995; Daubas et al., 2000). (D) Dissection of the head of a 12.5 dpc pEEBZ embryo reveals that the reporter expression is scattered but centred on the posterior mesencephalon extending into the pons. ß-galactosidase expression takes place predominantly outside of the previously described territories (red arrow indicates the boundary between the mesencephalon and the metencephalon; blue arrow indicates mamillary body; mes, mesencephalon; met, metencephalon).