Expression and localization of fukutin, POMGnT1, and POMT1 in the central nervous system: consideration for functions of fukutin.

Fukuyama-type congenital muscular dystrophy (FCMD), muscle-eye-brain disease (MEB), and Walker-Warburg syndrome (WWS) are congenital muscular dystrophies associated with central nervous system (CNS) lesions, represented by cobblestone lissencephaly and eye anomalies. The glia limitans, formed by astrocytic endfeet and covered with the basement membrane, is disrupted in fetal cases of these diseases. A gene responsible for FCMD is fukutin and that for MEB is protein O-linked mannose beta1,2-N-acetylglucosaminyltransferase (POMGnT1). Mutations in protein-O-mannosyltransferase 1 (POMT1) have been found in some WWS cases. POMGnT1 and POMT1 are involved in glycosylation of alpha-dystroglycan, which is one of the components of dystrophin-glycoprotein complex, linking dystrophin and extracellular matrix proteins at the basement membrane. Fukutin seems to have similar functions to those of POMGnT1 and POMT1, but its functions still remain to be clarified. In situ hybridization reveals that fukutin, POMGnT1, and POMT1 are expressed especially in astrocytes. Decrease of glycosylated alpha-dystroglycan has been reported in the skeletal muscle of FCMD, MEB, and WWS. Moreover, decrease of fukutin and glycosylated alpha-dystroglycan is observed in the brain of FCMD cases. Because astrocytes are involved in basement membrane formation at the glia limitans, fukutin, POMGnT1, and POMT1 are considered to relate to the pathogenesis of CNS lesions, and fukutin may be related to glycosylation of alpha-dystroglycan. Fukutin, POMGnT1, and POMT1 are expressed in immature neurons, suggesting they are also involved in neuronal migration itself. POMGnT1 and POMT1 are expressed in many mature neurons, but fukutin is positive in a few mature neurons. FCMD is a rather mild disease among FCMD, MEB, and WWS, and POMGnT1 and POMT1 seems to have more critical roles compared to fukutin in mature neurons.