Gamma 1 laminin and its biologically active KDI-domain may guide axons in the floor plate of human embryonic spinal cord

Immunocytochemistry, in situ hybridization and Matrigel-embedded cultures were used to investigate the distribution of laminins during development of the human embryonic spinal cord (7-11 weeks). Our results indicate that alpha 1, beta 1, beta 3 and gamma 1 laminins localize as punctate deposits in the floor plate region in association with commissural fibers crossing the ventral midline. In addition, the neurite outgrowth domain of gamma 1 laminin accumulates heavily in the floor plate region, in the notochord and in GFAP-immunoreactive glial fibers of the embryonic spinal cord. In culture experiments, the biologically active KDI-domain of gamma 1 laminin selectively attracted directional outgrowth of neurites from explants of the dorsal spinal cord. The spatial and temporal colocalization of punctate deposits of laminins with nerve fibers crossing the ventral midline, and the guidance of neurites by the KDI-peptide domain, indicate that laminins, specifically the gamma 1 laminin, may be involved in guidance of axons during embryonic development of the human spinal cord.