Muscle Specific Kinase (MuSK) has been identified to be specific to the lineage of mammalian skeletal muscle. It has been demonstrated that MuSK is highly localized to the neuromuscular junction (NMJ) and it is a component of the receptor complex for nerve-derived factor, agrin. The activation of MuSK by agrin is a critical step in mediating the phosphorylation and aggregation of acetylcholine receptors, a hallmark of postsynaptic specialization of NMJ. Our laboratory has cloned the cDNA encoding Xenopus MuSK and we have reported that MuSK expression can be detected in myotomal muscle and neural tissues. In light of this evidence, it is of interest to further study the expression of MuSK in Xenopus tissues and to identify different forms of MuSK that may have novel functional roles. In...[ Read more ]

Muscle Specific Kinase (MuSK) has been identified to be specific to the lineage of mammalian skeletal muscle. It has been demonstrated that MuSK is highly localized to the neuromuscular junction (NMJ) and it is a component of the receptor complex for nerve-derived factor, agrin. The activation of MuSK by agrin is a critical step in mediating the phosphorylation and aggregation of acetylcholine receptors, a hallmark of postsynaptic specialization of NMJ. Our laboratory has cloned the cDNA encoding Xenopus MuSK and we have reported that MuSK expression can be detected in myotomal muscle and neural tissues. In light of this evidence, it is of interest to further study the expression of MuSK in Xenopus tissues and to identify different forms of MuSK that may have novel functional roles. In this study, spatial expression of MuSK in Xenopus was studied by Northern blot and Western blot analyses. It was demonstrated that MuSK was expressed in spleen and ovary, in addition to skeletal muscle. Domain composition of MuSK transcripts was also analyzed by Northern blot analysis. Besides, full length of MuSK was isolated from Xenopus spleen and ovary by reverse transcription polymerase chain reaction. Amino acid alignment of these forms of MuSK with MuSK previously identified in skeletal muscle revealed amino acid substitutions scattered in different regions of the spleen form and ovary form of MuSK. Also, it is noteworthy that there was truncation of the extracellular domains in the ovary form of MuSK. Taken together, our findings suggest that MuSK is not restricted to the skeletal muscle of Xenopus, its expression can be detected in other tissues, such as spleen and ovary. It raises the possibility that MuSK may be involved in other functions in addition to the formation of NMJ.