TCreERT2-mediated deletion of <i>ß-catenin</i> at different axial levels.

<p>All embryos shown, of the indicated genotype and stage, with or without a 48-hour Tam induction, were stained for expression of the markers <i>Uncx4.1</i> and <i>Msgn1</i>. Both markers were developed with the same color reaction, but they mark mutually exclusive domains: <i>Uncx4.1</i> is expressed only in stripes in the somites and <i>Msgn1</i> is expressed only in the PSM. <b>A–E</b> are lateral views and <b>F–J</b> are either dorsal views (<b>F–H</b>) or magnified views of the caudal end of the embryo immediately above (<b>I, J</b>). TCre-mediated deletion of <i>ß-catenin</i> causes caudal truncation and disorganized somites at E8.5 (<b>A, F</b>). These E8.5 defects are phenocopied in the Tam-induced TCreERT2; <i>ß-catenin ^flox/null</i> embryos (<b>C,H</b>) but not in the uninduced control (<b>B,G</b>), which is similar to a normal TCreERT2; <i>ß-catenin ^flox/wt</i> embryo (insert in <b>B</b>). Tam induction can produce similar somitogenesis defects later in E10.5 TCreERT2; <i>ß-catenin ^flox/null</i> embryo (<b>E, J</b>). The yellow arrow in <b>E</b> indicates the axial level where caudal somite defects begin as indicated by <i>Uncx4.1</i> staining. The red arrow in <b>J</b> points to residual <i>Msgn1</i> expression. Uninduced E10.5 TCreERT2; <i>ß-catenin ^flox/null</i> control embryos (<b>D, I</b>) are similar to TCreERT2; <i>ß-catenin ^flox/wt</i> embryos (insert in <b>D</b>).