Developmental Expression of the Xenopus Iaevis fos

Abstrad We have isolated the Xenopus Iaevis homologue of the protooncogene los. Nucleotide sequence analysis of the complementary DNA revealed a coding domain for a 370-amino acid protein which shares extensive sequence homology with the avian and mammalian fos protein. During Xenopus development, the los mRNA is present in the oocyte and egg stages and declines to relatively low levels by the mid-blastula transition. Transient expression of los can be seen during the late neurula and again at the tadpole stage. The los mRNA is uniformly distributed in the vegetal and animal poles of the oocytes. In a Xenopus kidney cell line, the fos gene can be transcriptionally adivated by serum growth fadors and 12-O-tetradecanoylphorbol-13-acetate, and the fos mRNA can be superinduced by cycloheximide. The X. Iaevis fos protein migrates as a series of bands around Mr 55,000 and is localized in the nucleus. Both the Xenopus fos RNA and fos proteins exhibit a short half-life analogous to that observed with their mammalian counterpart. The Xenopus fos protein readily associates with murine jun (AP-1) oncoprotein, and the complex binds efficiently to AP-1 recognition elements. Furthermore, the Xenopus fos protein collaborates with mammalian jun protein to adivate transcription from 1 2-O-tetradecanoylphorbol-1 3-acetateresponsive element. The differential expression of los during Xenopus development and its ability to regulate transcription in association with jun suggest a role during embryogenesis.