neptune, a Kruppel-like transcription factor that participates in primitive erythropoiesis in Xenopus

The specification of the erythroid lineage from hematopoietic stem cells re quires the expression and activity of lineage-specific transcription factor s. One transcription factor family that has several members involved in hem atopoiesis is the Kruppel-like factor (KLF) family [1]. For example, erythr oid KLF (EKLF) regulates beta -globin expression during erythroid different iation [2-6]. KLFs share a highly conserved zinc finger-based DNA binding d omain (DBD) that mediates binding to CACCC-box and GC-rich sites, both of w hich are frequently found in the promoters of hematopoietic genes. Here, we identified a novel Xenopus KLF gene, neptune, which is highly expressed in the ventral blood island (VBI), cranial ganglia, and hatching and cement g lands. neptune expression is induced in response to components of the BMP-4 signaling pathway in injected animal cap explants. Similar to its family m ember, EKLF, Neptune can bind CACCC-box and GC-rich DNA elements. We show t hat Neptune cooperates with the hematopoietic transcription factor XGATA-1 to enhance globin induction in animal cap explants. A fusion protein compri sed of Neptune's DBD and the Drosophila engrailed repressor domain suppress es the induction of globin in ventral marginal zones and in animal caps. Th ese studies demonstrate that Neptune is a positive regulator of primitive e rythropoiesis in Xenopus.