Cooperative Interaction of Xvent-2 and GATA-2 in the Activation of the Ventral Homeobox Gene Xvent-1B

Abstract

The Xvent family of homeobox transcription factors is essential for the establishment of the dorsal-ventral body axis during Xenopus embryogenesis. In contrast to Xvent-2B and other members of the Xvent-2 subfamily, Xvent-1B is not a direct response gene of bone morphogenetic protein-4 signaling. Xvent-1B is activated by Xvent-2, but CHX experiments revealed the requirement of additional factors. In this study, we report on the cooperative effect of Xvent-2 and the zinc finger transcription factor GATA-2 on the promoter of the Xvent-1B gene. We show that GATA-2 is a direct target gene of bone morphogenetic protein-4 and that GATA-2 interacts with Xvent-2 to activate transcription of Xvent-1B. Both transcription factors bind to distinct elements within the Xvent-1B promoter, and GATA-2 physically interacts with the C-terminal domain of Xvent-2. Promoter/reporter studies in Xenopus embryos revealed that full activation of Xvent-1B requires both Xvent-2 and GATA-2. Moreover, the two factors are sufficient to direct transcription of Xvent-1B in the presence of CHX at the ventral side of the embryo. The failure of both factors to activate Xvent-1B on the dorsal side suggests the existence of a dorsal inhibitor. This inhibitor is likely a component of the dorsal Wnt signaling pathway because nuclear translocation of ␤-catenin before midblastula transition results in a suppression of Xvent-1B transcription.

GATA-1-dependent transcriptional repression of GATA-2 via disruption of positive autoregulation and domain-wide chromatin remodeling

“…The models depict the regulation of GATA-2 transcription during hematopoiesis. BMP-4 signals activate GATA-2 at the earliest stages of hematopoiesis (33,35). The analysis described herein shows that GATA-2 binds the Ϫ2.8-kb site when the locus is transcriptionally active.…”

“…Based on the role of BMP-4 signaling in activating GATA-2 transcription early in hematopoiesis (33,35) and work described herein, we propose that BMP-4 induces levels of GATA-2 sufficient to establish positive autoregulation (Fig. 6).…”

“…BMP-4-dependent GATA-2 transcription occurs in Xenopus without new protein synthesis (35), indicating a direct transcriptional mechanism. BMP-4 signals to Smad transcription factors (36), but Smad sites have not been delineated in the GATA-2 locus.…”

The vent-like homeobox gene VENTX promotes human myeloid differentiation and is highly expressed in acute myeloid leukemia

“…In Xenopus, the vent1 subfamily includes genes such as xvent1, xvent1b, and pvi (12, 13), the vent2 family includes the genes xvent2, xvent2b, vox1, vox15, and xom genes (14). The pivotal role of xvent2 in modulating hematopoietic development was supported by observations that this member of the vent2 gene family can interact with key hematopoietic transcription factors such as GATA2, SMAD1, and the ets family transcription factor ERG and acts in establishing a positive autoregulatory loop of BMP4 activation by binding to its own promoter and the bmp4 promoter (15)(16)(17)(18).…”

“…There are no data linking VENTX or its target gene LEF1 to erythroid development. However, studies in Xenopus have shown that Xvent-2 can directly interact with the C-terminal domain of GATA-2, an essential transcription factor for erythroid development (15).…”