Differential expression of VegT and Antipodean protein isoforms in Xenopus

The VegT/Antipodean (Apod) gene is important for germ layer formation in Xe nopus. To investigate the role of this gene at the protein level, as oppose d to the RNA level, we have generated affinity purified polyclonal antibodi es to Apod, and for comparison, to the other early T-box proteins Xbrachyur y and Eomesodermin. An anti-VegT/Apod antibody reveals that there are two p rotein isoforms in Xenopus, one that we refer to as VegT and a smaller mole cular weight isoform that we refer to as Apod. These isoforms have differen t N-terminal domains resulting from developmentally regulated alternative s plicing of a primary transcript arising from a single VegT/Apod gene. VegT is maternally expressed. Its translation is blocked during oogenesis but th e protein is present from the egg until gastrulation in the presumptive end oderm. There is no evidence for zygotic expression of this isoform. Convers ely, the Apod protein isoform is expressed only after the onset of zygotic transcription in the presumptive mesoderm and is inducible by activin. We c onclude that the developmental role of VegT/Apod is mediated by two differe nt proteins, with entirely different patterns of expression and response to growth factors. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved .