Composition and methods using myelin-associated glycoprotein (MAG) and inhibitors thereof

A method for determining whether neurite outgrowth from a particular type of neuron at a particular age is stimulated or inhibited in the presence of an altered or mutated form of MAG which comprises the steps of:

• a) culturing a first sample of a selected neuronal cell type on a growth-permissive substrate in the absence of MAG;
• b) culturing a second sample of the selected neuronal cell type on a growth-permissive substrate comprising an altered or mutated form of bound MAG;
• and
• c) comparing the relative amount of neurite growth in the cultured cells of a) and b);
• wherein when the relative growth of neurites in the cultured cells of a) is greater than in b), the neuronal cell is inhibited by the presence of the altered or mutated form of MAG, and when the relative growth of neurites in the cultured cells of a) is less than in b), the neuronal cell is stimulated by the presence of the altered or mutated form of MAG.

A method for identifying a MAG-dependent neurite growth altering agent for a selected neuronal cell type which comprises the steps of:

• a) culturing a first sample of a selected neuronal cell type on a growth-permissive substrate in the absence of MAG;
• b) culturing a second sample of the selected neuronal cell type on a growth-permissive substrate comprising an altered or mutated form of bound MAG in an amount sufficient to alter neurite outgrowth from the cells compared to the first sample of cells cultured in the absence of MAG;
• c) incubating the cell cultures of a) and b) with a known relative concentration of a test agent for a time sufficient to allow neurite growth;
• and
• d) comparing the relative amount of neurite growth in the cultured cells of a) and b);
• wherein an agent that changes the relative growth of neurites in the cultured cells of a) and b) is identified as a MAG-dependent neurite growth altering agent.

A method for identifying a MAG-dependent neurite growth altering agent for a selected neuronal cell type comprising the steps of:

• a) culturing separate samples of a selected neuronal cell type on a growth-permissive substrate lacking MAG;
• b) culturing a first sample of a) with a known concentration of a traceable, soluble altered or mutated form of MAG;
• c) culturing a second sample of a) with a known concentration of a traceable, soluble form of a control protein lacking MAG activity;
• d) incubating the cultures of b) and c) with a known relative concentration of a test agent for a time sufficient to allow neurite growth;
• and
• e) comparing the relative amount of neurite growth in the cultured cells of c) and d);
• wherein an agent that changes the relative growth of neurites in the cultured cells of c) and d) is identified as a MAG-dependent neurite growth altering agent.