AN ANALYSIS OF ALTERNATIVELY SPLICED CD45 MESSENGER-RNA TRANSCRIPTS DURING T-CELL MATURATION IN HUMANS

CD45 is a transmembrane protein tyrosine phosphatase found on nucleate d hematopoietic cells. In humans, multiple protein isoforms of CD45 ar e produced by alternative mRNA splicing of exons 4, 5, and 6 coding fo r the extracellular portion. We measured all eight possible CD45 mRNA transcripts using RT-PCR in human thymocytes and T cell lines, We repo rt that only six mRNA transcripts are present in T cells. The high mw CD45 mRNA transcripts containing exon 4 correlated with the stage of T cell maturation: abundant high mw transcripts (30.7% of all CD45 mRNA transcripts) were present in immature, CD3-4-8- triple-negative thymo cytes which decreased (7.7%) in intermediate, CD4+8+ double-positive ( DP) thymocytes and then increased (13.8% or 16.8%) in mature, CD4+8- o r CD4-8+ single-positive thymocytes, In addition, there was a complex variation in the spliced mRNA transcripts coding for CD45R(O), CD45R(B ), CD45R(BC), CD45R(AB), and CD45R(ABC) protein isoforms. High mw CD45 mRNA transcripts accumulated immediately prior to an important physio logic event such as thymocyte expansion. In addition, we identified li nkage between RNA splicing of exons 5 and 6, and splicing of exon 5 on ly and exons 4, 5, and 6 in FACS-purified CD4+ and CD8+ thymocytes. Th ese data support the developmental regulation of alternatively spliced CD45 mRNA transcripts and suggest that specific CD45 isoforms may pla y an important role at critical stages of T cell development, (C) 1997 Academic Press.