TRANSCRIPTIONAL REGULATION OF VAV, A GENE EXPRESSED THROUGHOUT THE HEMATOPOIETIC COMPARTMENT

The vav gene is expressed in all hematopoietic but few other cell type s. To explore its unusual compartment-wide regulation, We cloned the m urine gene, sequenced its promoter region, identified DNase I hypersen sitive (HS) sites in the chromatin, and tested their promoter activity with a beta-galactosidase (beta-gal) reporter gene in cell lines and transgenic mice. Whereas fibroblasts had no HS sites, a myeloid and an erythroid cell line contained five, located 0.2 kb (HS1), 1.9 kb (HS2 ), and 3.6 kb (HS3) upstream from the transcription start and 0.6 kb ( HS4) and 10 kb (HS5) downstream. A vav DNA fragment including HS1 prom oted beta-gal expression in a myeloid but not a fibroblast line. Expre ssion in leukocytes of transgenic mice also required HS2 and HS5. Only hematopoietic organs contained beta-gal, but virtually all beta-gal() cells were B or T lymphocytes. Expression was always variegated (mos aic), and the proportion of beta-gal(+) cells declined with lymphoid m aturation and animal age. Thus, these vav regulatory elements promoted hematopoietic-specific expression in vivo, at least in lymphocytes, b ut the transgene was sporadically silenced. Maintaining pan-hematopoie tic expression may require additional vav elements or an alternative r eporter. (C) 1998 by The American Society of Hematology.