The Maternal CCAAT Box Transcription Factor Which Controls GATA-2 Expression Is Novel and Developmentally Regulated and Contains a Double-Stranded-RNA-Binding Subunit

ABSTRACT

The transcription factor GATA-2 is expressed at high levels in the nonneural ectoderm of the Xenopus embryo at neurula stages, with lower amounts of RNA present in the ventral mesoderm and endoderm. The promoter of the GATA-2 gene contains an inverted CCAAT box conserved among Xenopus laevis, humans, chickens, and mice. We have shown that this sequence is essential for GATA-2 transcription during early development and that the factor binding it is maternal. The DNA-binding activity of this factor is detectable in nuclei and chromatin bound only when zygotic GATA-2 transcription starts. Here we report the characterization of this factor, which we call CBTF (CCAAT box transcription factor). CBTF activity mainly appears late in oogenesis, when it is nuclear, and the complex has multiple subunits. We have identified one subunit of the factor as p122, aXenopus double-stranded-RNA-binding protein. The p122 protein is perinuclear during early embryonic development but moves from the cytoplasm into the nuclei of embryonic cells at stage 9, prior to the detection of CBTF activity in the nucleus. Thus, the accumulation of CBTF activity in the nucleus is a multistep process. We show that the p122 protein is expressed mainly in the ectoderm. Expression of p122 mRNA is more restricted, mainly to the anterior ectoderm and mesoderm and to the neural tube. Two properties of CBTF, its dual role and its cytoplasm-to-nucleus translocation, are shared with other vertebrate maternal transcription factors and may be general properties of these proteins.

ACKNOWLEDGMENTS

Rob Orford and Carl Robinson contributed equally to the work presented here.

We thank Alison Snape and Jim Smith for the cDNA expression library and Brenda Bass and Mike Wormington for reagents, discussions, and allowing us access to data prior to publication. We are also most grateful to Geoff Kneale, Colyn Crane-Robinson, and Sarah Newbury for comments on the manuscript.

This work was supported by the Wellcome Trust and the Biotechnology and Biological Sciences Research Council (U.K.).