Immunohistochemical expression of cell adhesion molecule L1 during development of the human brain.

We demonstrated the expression of neural cell adhesion molecule, L1, during human brain development by immunostaining with anti-L1 fibronectin domain antibody. In the human cerebellum, the inner half of the external granular and molecular layers, mostly parallel fibres, and the Purkinje cell layer were immunoreactive for L1 from the early foetal period of 13-15 gestational weeks (GW). Immunoreactivity was strongest in the molecular layer in the perinatal period. The subcortical white matter and dentate layer were immunoreactive in foetal life. In the human cerebrum, the outer half of the molecular layer, together with Cajal-Retzius cell bodies, were positively stained until 30-34 GW, when afferent fibres develop over the entire cortex. The fibres in the white matter were strongly immunopositive in the fascicles until early infancy. These results suggest that L1 is temporally and spatially expressed in the developing brain, and may play important roles in neural cell migration, neurite elongation, and axonal fasciculation.