REGULATION OF LINEAGE RESTRICTED HEMATOPOIETIC TRANSCRIPTION FACTORS IN CELL HYBRIDS

SCL, GATA-1, GATA-2 and GATA-3 encode lineage restricted haemopoietic transcription factors. We have previously shown that SCL, GATA-1 and G ATA-2 are expressed in multipotent progenitors prior to lineage commit ment, but are down-regulated during granulocyte/monocyte differentiati on. The phenomenon of gene extinction in cell hybrids may reveal negat ive regulatory mechanisms operating during normal differentiation. We have therefore analysed the regulation of SCL, GATA-1, GATA-2 and GATA -3 in cell hybrids formed by the fusion of cell lines representing dif ferent haemopoietic lineages. Expression of GATA-3 was extinguished in both human and murine erythroid x T cell hybrids, an observation whic h suggests that erythroid cells contain factors capable of repressing GATA-3 expression. By contrast expression of SCL, GATA-1 and GATA-2 wa s not extinguished in erythroid x T or in erythroid x B cell hybrids. These data suggest that T cells and B cells do not contain trams-actin g factors capable of down-regulating expression of SCL, GATA-1 or GATA -2 and therefore raise the possibility that a 'hit and run' mechanism may repress these genes during normal haemopoiesis, HpaII sites within the SCL promoter were unmethylated in erythroid cells but methylated in T cells. Erythroid x T and erythroid x B cell hybrids both methylat ed and unmethylated SCL thus implicating a heritable cis-acting mechan ism in the regulation of the SCL gene in lymphoid cell lines. These re sults provide the first analysis of SCL and GATA gene regulation in st able cell hybrids.