The goal of this work is to learn some of the mechanisms that brain cells use in vivo to migrate from where they are born (in the ventricular zone) to where they stop migrating and differentiate (in the tectal plate). After recent advances in vitro have uncovered some of the molecules involved in this process, it is now necessary to determine how regulated expression of specific molecules controls particular aspects of migration in the developing brain itself. Here, we will determine how artificially regulated gene expression of a few selected neural molecules affects migration in a region of an animal brain, the chicken optic tectum. The major experimental method we will use to misexpress individual molecules in the tectum is a technique of retrovirus-mediated gene transfer that we helped to develop over the past few years. With this method, tectal progenitor cells are infected in vivo, and later a cell's progeny are detected with a histochemical stain for the viral marker gene. This method was first used to uncover the lineage relationships between cells and their migratory routes during development. Then, it was used to show that we could interfere with the main, radial component of migration by using antisense-containing vectors against a suspected migratory molecule, beta1 integrin, to attenuate its expression in cells. We will now determine if a minor, but important, tangential route of migration is affected similarly by attenuating beta1 integrin, and which of several possible integrin alpha-beta1 heterodimers is responsible for the facets of migration that we have interfered with. We will determine which alpha integrin subunits are expressed on cells during migration and map distributions of possible substrates. We will then construct the appropriate antisense alpha vectors and perform in vivo migration experiments to determine if one or more heterodimer is responsible for the effects obtained with antisense beta1. Second, we will use this gene transfer strategy to determine whether two other suspected molecules, N- cadherin and contactin, are involved in radial and/or tangential migration. After mapping protein expression on cells during migration, vectors will be constructed that either attenuate or overexpress the protein and their effects will be determined on migrating tectal cells. Roles of these molecules will then be inferred from an analysis of any observed migrational defects that result from the molecule's misexpression.
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