Selective motoneuron outgrowth from the cord in the avian embryo.

Selective axonal growth at a series of branching points along pathways is essential for the establishment of precise motoneuron projections. In order to reveal some of the molecules responsible for this selective axonal growth of motoneurons, I investigated the phenomenon of why motoneurons extend axons outside the spinal cord whereas interneurons do not. The analyses of immunohistology and embryonic surgery strongly suggested that motoneurons actively select to grow out from the cord and that interneurons also actively select to grow within the cord. The staining pattern of two monoclonal antibodies obtained from crude homogenate of young chick embryos were spatially and temporally correlated with motoneuron axonal growth. The antigenic molecules of these monoclonal antibodies were purified for the purpose of revealing their functions.