TFII-I is a ubiquitously expressed transcription factor that positively or 
negatively regulates gene expression. TFII-I has been implicated in neuronal and 
immunologic diseases as well as in thymic epithelial cancer. Williams-Beuren 
Syndrome (WBS) is caused by a large hemizygous deletion on chromosome 7q11.23 
which encompasses 26-28 genes, including GTF2I, the human gene encoding TFII-I. 
A subset of WBS patients has recently been shown to present with macrocytosis, a 
mild anemia characterized by enlarged erythrocytes. We conditionally deleted the 
TFII-I/Gtf2i gene in adult mice by tamoxifen induced Cre-recombination. Bone 
marrow cells revealed defects in erythro-megakaryopoiesis and an increase in 
expression of the adult β-globin gene. The data show that TFII-I acts as a 
repressor of β-globin gene transcription and that it is implicated in the 
differentiation of erythro-megakaryocytic cells.