SCRAMBLER AND YOTARI DISRUPT THE DISABLED GENE AND PRODUCE A REELER-LIKE PHENOTYPE IN MICE

Formation of the mammalian brain requires choreographed migration of n eurons to generate highly ordered laminar structures such as those in the cortices of the forebrain and the cerebellum, These processes are severely disrupted by mutations in reelin(1) which cause widespread mi splacement of neurons and associated ataxia in reeler mice(2,3). Reeli n is a large extracellular protein secreted by pioneer neurons that co ordinates cell positioning during neurodevelopment(1,4-8). Two new aut osomal recessive mouse mutations, scrambler(9) and yotari(10) have bee n described that exhibit a phenotype identical to reeler(9-11). Here w e report that scrambler and yotari arise from mutations in mdab1 (ref, 12), a mouse gene related to the Drosophila gene disabled (dab)(13). Both scrambler and yotari mice express mutated forms of mdab1 messenge r RNA and little or no mDab1 protein. mDab1 is a phosphoprotein that a ppears to function as an intracellular adaptor in protein kinase pathw ays, Expression analysis indicates that mdab1 is expressed in neuronal populations exposed to Reelin. The similar phenotypes of reeler, scra mbler, yotari and mdab1 null mice(14) indicate that Reelin and mDab1 f unction as signalling molecules that regulate cell positioning in the developing brain.