THE L2 HNK-1 CARBOHYDRATE IS CARRIED BY THE MYELIN-ASSOCIATED GLYCOPROTEIN AND SULFATED GLUCURONYL GLYCOLIPIDS IN MUSCLE BUT NOT CUTANEOUS NERVES OF ADULT MICE/

We have previously shown that myelinating Schwann cells associated wit h motor, but not sensory, axons in peripheral nerves of adult mice exp ress the L2/HNK-1 carbohydrate epitope. This carbohydrate structure ca rried by glycolipids and neural cell adhesion molecules has been sugge sted to specifically foster regrowth of motor as opposed to sensory ax ons after infliction of a lesion. To determine which molecular compone nts may be the carriers of the L2 carbohydrate in motor axon-associate d myelinating Schwann cells, we have isolated the purely sensory, cuta neous branch and the mixed sensory and motor muscle branch of the femo ral nerve of adult mice, isolated the myelin fraction thereof and anal ysed the molecules expressing the L2 carbohydrate by several immunoche mical methods. L2 immunoreactivity in myelin of the muscle branch was four to five times higher than that of the cutaneous branch. The 110 k Da L2-immunoreactive glycoprotein in myelin of the muscle branch, whic h is not L2-immunoreactive in the cutaneous branch, was identified as the myelin-associated glycoprotein by a combination of immunoprecipita tion and Western blot analysis. Myelin extraction with organic solvent s additionally revealed the two L2-carrying glycolipids, which amounte d to similar to 40 ng glycolipid/mg dry weight in myelin of the muscle branch, whereas no significant amounts of the 12 glycolipids were fou nd in myelin of the cutaneous branch. These observations suggest an as tonishing degree of differential regulation of carbohydrate-synthesizi ng activities in myelinating Schwann cells.