Gfi1b and Gfi1 are 37- and 55-kDa transcriptional repressors that share common 
features such as a 20-amino acid (aa) N-terminal SNAG domain, a nonconserved 
intermediary domain, and 6 highly conserved C-terminal zinc fingers. Both gene 
loci are under autoregulatory and cross-regulatory feedback control. We have 
generated a reporter mouse strain by inserting the cDNA for green fluorescent 
protein (GFP) into the Gfi1b gene locus which allowed us to follow Gfi1b 
expression during hematopoiesis and lymphopoiesis by measuring green 
fluorescence. We found highly dynamic expression patterns of Gfi1b in erythroid 
cells, megakaryocytes, and their progenitor cells (MEPS) where Gfi1 is not 
detected. Vice versa, Gfi1b could not be found in granulocytes, activated 
macrophages, or their granulomonocytic precursors (GMPs) or in mature naive or 
activated lymphocytes where Gfi1 is expressed, suggesting a complementary 
regulation of both loci during hematopoiesis. However, Gfi1b was found to be 
up-regulated in early stages of B-cell and in a subset of early T-cell 
development, where Gfi1 is also present, suggesting that cross-regulation of 
both loci exists but is cell-type specific.