NUCLEAR TRANSLOCATION OF A MATERNAL CCAAT FACTOR AT THE START OF GASTRULATION ACTIVATES XENOPUS GATA-2 TRANSCRIPTION

The transcription factor GATA-2 is present in blood cell precursors an d plays a pivotal role in the control of erythroid differentiation. In Xenopus embryos, low levels of GATA-2 mRNA are maternally derived, wh ile the onset of zygotic GATA-2 expression coincides with commitment t o haematopoietic lineages, However, its initial transcriptional activa tion is not restricted to the presumptive blood islands, but occurs th roughout ventral and lateral regions, in all three germ layers, In ord er to determine how this expression pattern is controlled, we have iso lated and characterized the Xenopus GATA-2 gene, We show that 1.65 kb of 5' flanking sequences are sufficient to direct both correct transcr iptional initiation in oocytes and appropriate temporal and spatial ge ne expression in early embryos, The transgene is activated during gast rulation and by neurula stages is predominantly expressed in the ventr al hemisphere, We demonstrate that a CCAAT element is necessary for ge ne activity in both systems and that extracts prepared from oocytes an d embryos contain a factor which specifically recognizes this element, We also show that cytoplasmic localization inhibits the function of t his CCAAT factor until the beginning of gastrulation, when the zygotic GATA-2 gene is activated, These observations extend our understanding of the mechanisms by which maternal factors control the temporal acti vation of transcription in early vertebrate embryos.