TRANSGENIC XENOPUS EMBRYOS FROM SPERM NUCLEAR TRANSPLANTATIONS REVEALFGF SIGNALING REQUIREMENTS DURING GASTRULATION

We have developed a simple approach for large-scale transgenesis in Xe nopus laevis embryos and have used this method to identify in vivo req uirements for FGF signaling during gastrulation, Plasmids are introduc ed into decondensed sperm nuclei in vitro using restriction enzyme-med iated integration (REMI). Transplantation of these nuclei into unferti lized eggs yields hundreds of normal, diploid embryos per day which de velop to advanced stages and express integrated plasmids nonmosaically , Transgenic expression of a dominant negative mutant of the FGF recep tor (XFD) after the mid-blastula stage uncouples mesoderm induction, w hich is normal, from maintenance of mesodermal markers, which is lost during gastrulation. By contrast, embryos expressing XFD contain well- patterned nervous systems despite a putative role for FGF in neural in duction.