FIGURE 4.

Localization of a follistatin repression domain. A-D, chick embryo neural tubes were electroporated on the left side with wild type or truncated Krox20 expression constructs, as indicated, in situ hybridized with the follistatin probe, and flat mounted. This reveals a partial repression of follistatin gene expression, which is lost upon deletion of the 235 N-terminal amino acids. E and F, similar analysis of Hoxb1 expression shows a repression by Krox20, which is maintained upon elimination of most of the N-terminal region, with, however, a slight reduction. This latter effect might be an indirect consequence of the lack of induction of endogenous Krox20 by Krox20 Δ1-258.