Regulation of the PU.1 gene by distal elements

The transcription factor PU.1 (also known as Spi-1) plays a critical role i n the development of the myeloid lineages, and myeloid cells derived from P U.1(-/-) animals are blocked at the earliest stage of myeloid differentiati on. Expression of the PU.1 gene is tightly regulated during normal hematopo ietic development, and dysregulation of PU.1 expression can lead to erythro leukemia. However, relatively little is known about how the PU.1 gene is re gulated in vivo. Here it is shown that myeloid cell type-specific expressio n of PU.1 in stable cell lines and transgenic animals is conferred by a 91- kilobase(kb) murine genomic DNA fragment that consists of the entire PU.1 g ene (20 kb) plus approximately 35 kb of upstream and downstream sequences, respectively. To further map the important transcriptional regulatory eleme nts, deoxyribonuclease I hypersensitive site mapping studies revealed at le ast 3 clusters in the PU.1 gene. A 3.5-kb fragment containing one of these deoxyribonuclease I hypersensitive sites, located -14 kb 5' of the transcri ptional start site, conferred myeloid cell type-specific expression in stab ly transfected cell lines, suggesting that within this region is an element important for myeloid specific expression of PU.1. Further analysis of thi s myeloid-specific regulatory element will provide insight into the regulat ion of this key transcriptional regulator and may be useful as a too[ for t argeting expression to the myeloid lineage. (C) 2001 by The American Societ y of Hematology.