FYN CAN PARTIALLY SUBSTITUTE FOR LCK IN T-LYMPHOCYTE DEVELOPMENT

Lck, a Src family tyrosine kinase, transduces signals important for th e development of alpha beta and gamma delta T cells. However, T cell d evelopment is only partially compromised in Lck-deficient mice, sugges ting that other kinases may also transduce pre-TCR or TCR signals. One candidate is Fyn, a Src kinase coexpressed with Lck in immature and m ature T cells. Here we show that T cell development is completely comp romised in lck(-/-)fyn(-/-) mice. In addition, we demonstrate that exp ression of a gain-of-function mutant fyn(T) transgene completely resto res production of immature CD4/CD8 double positive thymocytes and gamm a delta T cells and improves the representation of CD4 or CD8 single p ositive thymocytes. These observations reveal that Fyn can subserve so me Lck-like functions in T cell development.