| Abstract: | Embryos of the axolotl affected with the cardiac-lethal mutation form hearts that never begin to beat. A number of other traits characteristic of the mutant phenotype, including edema, underdeveloped gills, shorter stature, and aphagia (the inability to feed), were believed to be secondary effects of the absence of circulation. We have recently demonstrated that the pre-cardiac mesoderm is directly affected by the c gene, making it unresponsive to normal inductive signals. In this study, we replaced part or all of the mutant pre-cardiac mesoderm with wild-type tissue, to produce embryos with normally beating hearts and circulation. As expected, most of the other mutant characteristics were also corrected. However, otherwise normal individuals remained aphagic. All embryos with beating hearts containing mutant tissue also suffered from an unexpected circulatory arrest some time after the onset of circulation. This apparently indicates that there are at least two tissues other than the myocardium which appear to be directly affected by the c gene. These previously unsuspected pleiotropic effects of the mutation may involve poorly-characterized mesodermal-neural crest inductive interactions and may also lead to a greater understanding of the link between congenital heart defects and feeding difficulties in humans. © 1993Wiley-Liss, Inc. |
