DIFFERENTIAL EXPRESSION OF PTP1D, A PROTEIN-TYROSINE-PHOSPHATASE WITH2 SH2 DOMAINS, IN SLOW AND FAST SKELETAL-MUSCLE FIBERS

We show that PTP1D, a protein tyrosine phosphatase that contains two S H2 domains, is preferentially expressed in slow skeletal muscle fibers . Immunohistochemical staining using polyclonal antibodies against PTP 1D demonstrated that PTP1D was expressed in a subpopulation of rodent muscle fibers. These fibers were identified as slow Type I fibers base d on histochemical ATPase assays and slow myosin heavy chain expressio n. Northern and Western analyses showed that PTP1D levels were higher in predominantly slow muscles than in predominantly fast muscles. This differential expression of PTP1D in slow muscle fibers appeared by bi rth. In cultures of mouse myogenic cells, PTP1D was expressed after My oD and myogenin and appeared in myotubes derived from embryonic, fetal , and postnatal myoblasts. Remarkably, PTP1D was organized into sarcom eres in a pattern coincident with myosin heavy chain, suggesting that PTP1D associates with a component of the thick filament. These results show that PTP1D is preferentially expressed in slow muscle fibers, We speculate that PTP1D may play a role in slow muscle fiber function an d differentiation. (C) 1996 Academic Press, Inc.