Genomic organization and modulation of gene expression of the TGF-ß and FGF pathways in the allotetraploid frog Xenopus laevis.

Inductive interactions mediated by the TGF-ß and FGF-MAPK pathways are essential for specification of the germ layers and embryonic body axes during early vertebrate embryogenesis. TGF-ß and FGF ligands signal through receptor Ser/Thr and Tyr kinases, respectively, and these signaling pathways cross-talk to regulate transcription and cell behavior. The allotetraploid Xenopus laevis and its ancestral diploid Xenopus tropicalis are versatile model organisms with which to study the inductive interactions and mechanisms of these signal transduction pathways. Here we have analyzed the draft genome of X. laevis with respect to the genomic organization and differential expression of genes in the TGF-ß and FGF pathways. Genomic structure and gene expression analyses of pathway components in X. laevis revealed that genetic modulations, including deletions resulting in singletons and differential expression of homeologs, have occurred frequently among extracellular regulatory factors of the TGF-ß pathway after allotetraploidization. Moreover, differential gene expression was found for factors regulating various cellular responses including co-receptors, decoy receptors, and intracellular negative regulators in both the TGF-ß and FGF-MAPK pathways. We summarize the patterns of genetic alterations in the allotetraploid frog X. laevis and discuss the importance of these changes with regard to developmental processes.