Fig. 7. Overexpression of hyperventralizing xTsg constructs in zebrafish embryos inhibits dorsoanterior development. (A) Uninjected sibling. Wild-type zebrafish embryos were injected at the one-cell stage with 400 pg wild-type xTsg mRNA (B-D) or with 330 pg xTsg^W67G mRNA (E-G). Embryos injected with wild-type xTsg mRNA in two independent experiments (n=144) displayed a range of dorsalization (as classified by Mullins et al., 1996): 13% Class 1 (not shown), 44% Class 2 (B), 17% Class 3 (C) and 24% Class 4 (D). Of the embryos displaying Class 1 or 2 dorsalizations, 51% also exhibited duplication of the terminal ventral fin (inset in B, indicated by arrowheads), suggestive of a tail ventralization in zebrafish. Of 199 embryos injected with 330 pg xTsg^W67G mRNA in two independent experiments, 73% were moderately ventralized to levels comparable with chordino (E). 14% showed a phenotype more severe than chordino (F) and 3% displayed an even more ventralized phenotype (G). At higher doses (800 pg), xTsg^W67G mRNA caused phenotypes stronger than chordino in 86.8% of embryos (n=91), with 18.7% of the type shown in G and 67% of the type shown in F. Note the almost complete absence of brain and trunk somites in G. Injection of 200 pg xTsg^C59A mRNA into 60 embryos (not shown) also caused ventralization, with 82% appearing similar to E, and 5% resembling F.