Schwann cell myelination occurred without basal lamina formation in laminin alpha 2 chain-null mutant (dy(3K)/dy(3K)) mice

The laminin alpha2 chain is a major component of basal lamina in both skele tal muscle and the peripheral nervous system. Laminin alpha2 chain deficien cy causes merosin-deficient congenital muscular dystrophy, which affects no t only skeletal muscles, but also the peripheral and central nervous system s. It has been reported that the formation of basal lamina is required for myelination in the peripheral nervous system. In fact, the spinal root of d ystrophic mice (dy/dy mice), whose laminin alpha2 chain expression is great ly reduced, shows lack of basal lamina and clusters of naked axons. To inve stigate the role of laminin alpha2 chain and basal lamina in vivo, we exami ned the peripheral nervous system of dy(3K)/dy(3K)mice, which are null muta nts of laminin alpha2 chain. The results indicate the presence of myelinati on although Schwann cells lacked basal lamina in the spinal roots of dy(3K) /dy(3K) mice, suggesting that basal lamina is not an absolute requirement f or myelination in vivo. Immunohistochemically, the expression of laminin al pha4 chain was increased and laminin alpha5 chain was preserved in the endo neurium of the spinal root. Laminin alpha4 and alpha5 chains may play the c ritical role in myelination instead of laminin alpha2 chain in dy(3K)/dy(3K )mice. In addition, the motor conduction velocity of the sciatic nerve was significantly reduced compared with that of wild-type littermate. This redu ction in conduction velocity may be due to small axon diameter, thin myelin sheath and the patchy disruption of the basal lamina of the nodes of Ranvi er in dy(3K)/dy(3K)mice. (C) 2001 Wiley-Liss, Inc.