Fig. 6

Schematic illustration of zebrafish cranial mesoderm pattering at early development stage (3ss) in comparison with chick embryo (HH6). Dorsal view of a zebrafish embryo at 3ss and the rostral region of a chick embryo at HH6. By the end of gastrulation, a distinct group of cells form the polster which lies at most anterior part of the prechordal plate mesoderm. These cells are marked by the expression of pitx2 (yellow, left) in zebrafish but not in chick. Posterior to the polster, the zebrafish cranial mesoderm (left) resolves into three bilateral strips along the mediolateral axis. The innermost region is the cranial paraxial mesoderm (dark blue) located adjacent to the notochord and marked by the expressions of foxc1a and fsta; lateral to the paraxial mesoderm is the cranial lateral mesoderm (red) marked by the expression of tbx1, cyp26c1 and alx1 genes; the outermost strip is the anterior lateral plate mesoderm (ALPM, green) labelled with tbx20. Note that tbx1 gene is also expressed in the posterior region (*) of the cranial paraxial mesoderm. The boundaries between the three mediolateral strips partially overlap. In contrast to zebrafish embryos, chick head mesoderm lacks the intermediate strip (red) of cranial lateral mesoderm. Instead, the paraxial mesoderm marked by FoxC1 (dark blue) is further sub-regionalised into the anterior part marked by Pitx2 (yellow/blue stripes) and posterior (*) by Tbx1 (red/blue stripes). Chick Tbx20 (green) is expressed in both anterior and posterior lateral mesoderm at this stage