Dual functions of Dab1 during brain development.

Area of Science:

• Neuroscience
• Developmental Biology
• Molecular Biology

Background:

• Reelin is a crucial signaling molecule for neuronal migration during brain development.
• It signals via the Disabled-1 (Dab1) adaptor protein and Src family kinases.
• Dab1 phosphorylation activates Akt and scaffolds signaling complexes, including Crk/CrkL adaptors, but its developmental roles remain unclear.

Purpose of the Study:

• To elucidate the specific roles of Dab1 tyrosine phosphorylation sites in Reelin signaling during brain development.
• To determine the necessity of distinct Dab1 phosphorylation sites for Akt activation, Dab1 turnover, and Crk/CrkL pathway engagement.

Main Methods:

• Generation of two distinct Disabled-1 (Dab1) mutant alleles, each lacking two of the four putative tyrosine phosphorylation sites.
• Analysis of brain development in mice carrying these mutant Dab1 alleles, assessing complementation between alleles.
• Investigation of Reelin-induced signaling events, including Akt activation, Dab1 phosphorylation, Dab1 protein levels, and Crk/CrkL-C3G pathway activation.

Main Results:

• Neither single mutant Dab1 allele supported normal brain development, but they exhibited functional complementation, indicating distinct roles for the mutated sites.
• Two specific tyrosine sites on Dab1 are essential for Reelin-mediated Akt activation and downregulation of Dab1 protein levels.
• The other two tyrosine sites are required for Reelin to stimulate the Crk/CrkL-C3G signaling pathway, and their absence leads to abnormal neuronal layering.

Conclusions:

• Reelin-induced Akt activation and Dab1 protein turnover are insufficient for normal brain development.
• Distinct tyrosine phosphorylation sites on Dab1 mediate separate Reelin signaling outputs.
• Dab1 functions both as a kinase switch and a scaffold in vivo, integrating multiple signaling pathways for proper neuronal development.