Laminin-1 selectively stimulates neuron generation from cultured retinal neuroepithelial cells

Signals derived from the extracellular matrix (ECM) largely influence neuron differentiation and development. However, the action of specific ECM components in these processes is poorly understood. This had led us to investigate the role of different laminins in the survival, proliferation, and neuron differentiation of cultured neuroepithelial cells from the developing chicken retina. Dissociated retinal neuroepithelial cells from 5-day-old chicken embryos, cultured on laminin-1, survived, proliferated, and differentiated into neurons, as assessed by both [3H]-thymidine uptake and acquisition of neuronal markers. Nevertheless, these effects took place only in the presence of cell-cell contact. In contrast, RN22 Schwannoma-derived laminin (devoid of alpha 1 chain) and merosin (bearing an alpha 2 chain), which also promoted proliferation when cell-cell contact occurred, led to reduced cell survival and failed to foster neuron differentiation. Furthermore, the laminin-1 P1 fragment (containing the rod-like portions of the short arms of the molecule) also failed to support neuron generation. In contrast, the laminin-1 E8 fragment (containing the long arm of the molecule) supported such a process to the same extent as the whole laminin-1 molecule, although a similar activity cannot be ruled out in other globular domains of the short arms. However, these results stress the importance of the carboxy-terminal part of alpha 1 chain in neuronal development. A cDNA fragment of a chicken alpha 1 chain was cloned and semiquantitative PCR amplification revealed that its mRNA is expressed in retinal neuroepithelial cells at the time of neuron differentiation. Our data strongly suggest that an alpha 1-like chain-containing laminin is needed for differentiation of neuron precursor cells.