Xenopus Xenf: an early endodermal nuclear factor that is regulated in a pathway distinct from Sox17 and Mix-related gene pathways

We report a novel zygotic gene encoding a Xenopus endodermal nuclear factor , Xenf. Expression of Xenf starts at the late blastula stages and is decrea sed after gastrulation. Xenf shows no structural homology to any known prot eins. When GFP-tagged Xenf is overexpressed in Xenopus cells, Xenf protein is localized to the nucleus, associating closely with the chromosomes. In a nimal cap assays, Xenf expression is strongly activated by mRNA injection o f Vg1 and VegT, maternal vegetal genes that can induce endodermal different iation.. In contrast, Xenf is not induced by endoderm-inducing zygotic tran scription factors such as Sox17 and Mix-related genes. Ln rum, Xenf does no t activate expression of Sox17, Mixer or Milk. Thus, Xenf is regulated by m aternal vegetal positional information in a parallel manner to Sox17 and Mi x-related gene pathways. (C) 2000 Elsevier Science ireland Ltd. All rights reserved.