EXPRESSION OF TYROSINE KINASE GENES IN MOUSE THYMIC STROMAL CELLS

Amongst the most important signal transduction molecules involved in r egulating growth and differentiation are the protein tyrosine kinases (PTK), Since T cell development is a consequence of interactions betwe en thymic stromal cells (TSC) and thymocytes, identification of the PT K in both compartments is required to dissect the mechanisms that cont rol this process, Here we report a search for PTK in mouse TSC, using RT-PCR to survey the repertoire of PTK mRNAs expressed in a freshly is olated TSC preparation, We identified 10 different PTK cDNAs among the 216 cDNAs sequenced, and demonstrate that transcripts of three of tho se (ufo, fyn and for) are widely expressed among a large panel of immo rtalized thymic epithelial cell lines (TEC) and in primary cultures of TSC, Of the other seven, none were expressed in established TEC lines but, instead, displayed distinct expression patterns in cell types li kely to have contaminated the fresh TSC preparation, i.e. macrophages, B cells, T cells and fibroblasts, Among the three PTK expressed in TE C lines, only one, ufo, exhibited expression exclusively in cells of n on-hemopoietic origin, Although expression of ufo (also known as tyro 7, axl or ark) is not thymic-specific, in that it is also expressed in cell types of mesodermal origin in other tissues, its presence in TEC suggests a role for ufo in differentiation of the TSC compartment, Co nsistent with this notion, high-level expression of this receptor PTK at the protein level could be documented in every TEC line investigate d, as well as in fresh thymus tissue sections, These data provide the first example of a receptor PTK in TSC and open new approaches to stud y the regulation of TSC differentiation.