| Research Abstract |
The present research aim is to provide better understanding the cellular and molecular mechanisms of cortical development, especially the interplay of reelin signal cascade with cortical cell's alignment. In the neurological mutant mice reeler, the various classes of cortical neurons are generated and complete their migration at the normal time, however, the cellular pattern in the radial dimension is distorted, i.e., the cortical lamination is roughly inverted. We showed experimentally that Reelin, the product of the reeler gene (Reln) and secreted from the Cajal-Retzius cells, provides an instructive signal for migrating cortical neurons to align at appropriate location ill developing cortex. Using a unique antibody CR-50 which recognizes Reelin, we showed that Reelin binds each other to form a huge protein complex and suggested that this assembly formation is critical for its function. The reeler phenotype is also observed in yotari mutant mice lacking the mdab1 gene which encodes s
… More
ignal transduction-associated protein Dab1. We have found that the yotari mutation is caused by a replacement of dab1 gene sequence with a long interspersed nuclear element (L1) fragment. Unlike Reelin, Dab1 is expressed in the cortical plate neurons, resides in the cytoplasm and interacts with tyrosine kinases of the Src family. In addition, phosphorylation of Dab1 is decreased in reeler, but increased when Reelin is added to cortical cell cultures. These observations indicated the presence of the Reelin receptors in the cell membrane of the cortical plate neurons that sense the extracellular Reelin, couple with tyrosine kinases and relay this signal to the cell via Dab1. Yagi group had previously showed that Fyntyrosine kinase has a crucial molecular function in building brain network and isolated a novel cadherin-related neuronal receptor (CNR) family proteins localized on the cell membrane of the cortical neurons using Fyn binding activity from the mouse brain. Collaborating with Yagi group, we identified a CNR family as a candidate of Reelin receptors. In addition to CNRs, two membrane proteins, apoER2 and VLDLR, have been identified as Reelan receptors. We provided antibodies against these receptor proteins and showed that extracellular Reelin proteins and these receptor proteins are co-localized on the processes of cortical plate neurons. We are now investigating how these receptors act in concert as components of the Reelin receptors. Less
|
