Fig. 1. The Cyc pro-domain is essential for its activity. (A) Schematic representation of the Cyc precursor, Cyc^pro, Cyc^mat, Activin^pro:Cyc^mat fusion, Sqt precursor, Sqt^mat, hNODAL precursor and hNODAL^mat. L indicates the leader (hatched boxes), Pro and Mat indicate the pro-domain and the mature domain, respectively. Cleavage sites between the pro- and mature regions are shown for each precursor molecule. (B) Analysis of induction of gsc by overexpression of RNA encoding Cyc, Sqt and hNODAL. RNA was injected at 0.5, 5 and 25 pg doses into one-cell wild-type embryos and expression of gsc was examined at 50% epiboly. Animal pole views of embryos showing endogenous gsc expression (I), and mild (II) or massive (III and IV) expansion of the gsc expression domains. Embryos were assessed and counted accordingly. Percentages for each class are shown in the histogram. Scale bar: 100 µm. (C) Induction of ntl by overexpression of RNA encoding Cyc, Sqt and hNODAL. Animal pole views of embryos showing endogenous ntl expression (I), mild expansion (II) or massive expansion (III and IV) of the ntl expression domains. Embryos were assessed and scored accordingly. Percentages for each class are shown in the histogram. Unlike hNODAL^mat or Sqt^mat, Cyc^mat has no discernible gsc- or ntl-inducing activity, and the Cyc pro-domain is required for its activity. Scale bar: 100 µm.