Identification of reelin-induced sites of tyrosyl phosphorylation on disabled 1

The study of mice with spontaneous and targeted mutations has uncovered a s ignaling pathway that controls neuronal positioning during mammalian brain development. Mice with disruptions in reelin, dab1, or both vldlr and apoER 2 are ataxic, and they exhibit severe lamination defects within several bra in structures. Reelin is a secreted extracellular protein that binds to the very low density lipoprotein receptor and the apolipoprotein E receptor 2 on the surface of neurons. Disabled-1 (Dab1), an intracellular adapter prot ein containing a PTB (phosphotyrosine binding) domain, is tyrosyl-phosphory lated during embryogenesis, but it accumulates in a hypophosphorylated form in mice lacking Reelin or both very low density lipoprotein receptor and a polipoprotein E receptor 2, Dab1 is rapidly phosphorylated when neurons iso lated from embryonic brains are stimulated with Reelin, and several tyrosin es have been implicated in this response. Mice with phenylalanine substitut ions of all five tyrosines (Tyr(185), Tyr(198), Tyr(200), Tyr(220), and Tyr (232)) exhibit a reeler phenotype, implying that tyrosine phosphorylation i s critical for Dab1 function. Here we report that, although Src can phospho rylate all five tyrosines in vitro, Tyr(198) and Tyr(220) represent the maj or sites of Reelin-induced Dab1 phosphorylation in embryonic neurons.