Of note in the above experiments, the effect of the ZIC1 C-terminal mutants was to increase the expression of the Xenopus target gene en-2 (Figures 3B and 3C). Given previous evidence that the paralogous gene En1 is critical for early biogenesis of the murine coronal suture,11 we asked whether Zic1 might also be expressed in relevant cells. Although the neural pattern of Zic1 expression20,41 and loss-of-function phenotypes19,20 were previously described in the mouse, no evidence has linked Zic1 expression to coronal suture development. Therefore, we analyzed expression patterns of Zic1 in embryonic mouse heads between E11.5 and E17.5. Between E11.5 and E12.5, a distinct domain of Zic1 expression was observed in the supraorbital region and cephalic mesoderm, which appeared to precede and partly overlap En1 expression (Figure 4). By contrast, no Zic1 expression was observed in the calvaria at E14.5 and E17.5 (not shown).