Signaling clusters caught in the act

Biochemical studies have provided a detailed accounting of the molecules present in the T cell receptor (TCR) complex during T cell activation, but relatively little is known about the maturation and dynamic composition of these complexes. Now Bunnell et al., reporting on page 1263, have developed a novel assay that allows them to visualize the formation of these complexes in live cells.

The authors dropped live Jurkat leukemic T cells onto coverslips coated with anti-TCR antibodies, and then tracked chimeric signaling proteins as they associated with and dissociated from signaling complexes. TCR-signaling complexes develop within 15 s, and undergo dynamic assembly and disassembly throughout the process of contact formation. Initial clustering of the TCRs does not require phosphotyrosine-dependent interactions, but the formation of a functional signaling complex does. A lipid raft marker does not localize to the...