THE HEAT-STABLE ANTIGEN (MOUSE-CD24) GENE IS DIFFERENTIALLY REGULATEDBUT HAS A HOUSEKEEPING PROMOTER

Expression of the mouse heat stable antigen (HSA or mouse CD24) shows tissue-specific as well as developmental regulation. During the matura tion of several hematopoietic lineages, HSA expression is generally hi gh in immature precursor cells and low or absent in terminally differe ntiated cells. We present evidence suggesting that this regulation of the HSA gene (Cd24a) occurs at the transcriptional level. In addition, sequence and methylation analysis of the Cd24a promoter revealed char acteristics of both ''housekeeping'' and tissue-specific promoters, in cluding a methylation-free, HpaII tiny fragment (HTF) island, multiple putative SP1 and AP-2 consensus binding sites, and a TATA box. Functi onal analysis of a 0.6-kilobase DNA fragment containing these elements fused to the CAT reporter gene in transient transfection experiments showed activity in both HSA expressing and non-expressing cell lines w ith a strength similar to that of the herpes-simplex virus-thymidine k inase promoter. Large fragments from the flanking region of the Cd24a promoter did not influence the ubiquitous nature of this promoter. Fin ally, we mapped the Cd24a, Cd24b, and Cd24c genes to mouse chromosomes 10, 8, and 14 respectively.