Dual Functions of Dab1 during Brain Development

Abstract

Reelin coordinates the movements of neurons during brain development by signaling through the Dab1 adaptor and Src family tyrosine kinases. Experiments with cultured neurons have shown that when Dab1 is phosphorylated on tyrosine, it activates Akt and provides a scaffold for assembling signaling complexes, including the paralogous Crk and CrkL adaptors. The roles of Akt and Dab1 complexes during development have been unclear. We have generated two Dab1 alleles, each lacking two out of the four putative tyrosine phosphorylation sites. Neither allele supports normal brain development, but each allele complements the other. Two tyrosines are required for Reelin to stimulate Dab1 phosphorylation at the other sites, to activate Akt, and to downregulate Dab1 levels. The other two tyrosines are required to stimulate a Crk/CrkL-C3G pathway. The absence of Crk/CrkL binding sites and C3G activation causes an unusual layering phenotype. These results show that Reelin-induced Akt stimulation and Dab1 turnover are not sufficient for normal development and suggest that Dab1 acts both as a kinase switch and as a scaffold for assembling signaling complexes in vivo.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/ .

ACKNOWLEDGMENTS

We thank Esther Jhingan for expert technical assistance, Nanyang Jiang for blastocyst injections, Brian Howell and Lionel Arnaud for constructs, Robert McEvilly and Robert Hevner for generous gifts of antisera, Philippe Soriano for cryostat and microscope use, and members of the Cooper laboratory for interesting discussions. We greatly appreciate Yves Jossin for his thoughtful comments on the paper.

This work was supported by U.S. Public Health Service grant CA41072 from the National Cancer Institute.