DEVELOPMENTALLY-REGULATED EXPRESSION OF A MURINE RECEPTOR-TYPE PROTEIN-TYROSINE-PHOSPHATASE IN THE THYMUS

Reversible phosphorylation of tyrosine residues plays a crucial regula tory role in various cellular events, including differentiation and pr oliferation of lymphocytes. Here, we report the isolation of a murine receptor-type protein tyrosine phosphatase (PTP), mRPTP-sigma, which i s expressed in both immature thymocytes and stroma cells. At least two alternatively spliced transcripts of mRPTP-sigma (T and B) were obser ved. mRPTP-sigma T was the dominant form in the thymus and had three I g-like and eight fibronectin type III-like domains in the extracellula r portion. mRPTP-sigma T was almost identical with RPTP-sigma/PTP NE-3 /PTP-P1/CPTP1, a PTP recently cloned from rat brain, except that RPTP- sigma/PTP NE-3/PTP-P1 was about 400 amino acids shorter than mRPTP-sig ma T. mRPTP-sigma B, the second form of mRPTP-sigma, was dominant in t he brain and was most likely the murine counterpart of RPTP-sigma/PTP NE-3/PTP-P1. In the developing thymocytes, the expression of mRPTP-sig ma was high in double negative (CD4(-)CD8(-)), low in double positive (CD4(+)CD8(+)), and marginal in single positive (SP; CD4(+)CD8(-) or C D4(-)CD8(+)) subpopulations. No upregulation of mRPTP-sigma was observ ed in the spleen cells stimulated with Con A. Developmental regulation of mRPTP-sigma expression suggests its involvement in the control of T lymphocyte differentiation.