CLONING OF CDNAS ENCODING XENOPUS NEUREGULIN - EXPRESSION IN MYOTOMALMUSCLE DURING EMBRYO DEVELOPMENT

Neuregulin has diverse functions in neural development, and one of the m is the up regulation of acetylcholine receptors (AChRs) at the muscl e fiber during the formation of neuromuscular junctions. Although the primary source of neuregulin is derived from motor neuron, the express ion in muscle has also been demonstrated. The precise role of neuron-d erived and muscle-derived neuregulin during the early stages of develo pment is not known. In order to study the role of neuregulin during ea rly embryo development, we isolated the cDNAs encoding Xenopus neuregu lin by cross-hybridization with its chick homologue. The amino acid se quence of Xenopus protein is 50 to 70% identical to members of the neu regulin family. The cDNAs encoding different isoforms of Xenopus neure gulin were identified, and these isoforms have two variation sites: (i ) the spacer domain with either 0 or 43 amino acid insertion; and (ii) the C-terminus of EGF-like domain to derive either alpha or beta isof orm. When the EGF-like domain of Xenopus neuregulin was expressed in m ammalian cells, the recombinant protein was able to induce the express ion of AChR and the tyrosine phosphorylation of erbB receptors in cult ured myotubes. An similar to 6.5 kb transcript corresponding to neureg ulin was detected in RNA isolated from brain and muscle. Various splic ing variants were expressed in different Xenopus tissues. In situ hybr idization showed a strong expression of neuregulin in developing brain and spinal cord of Xenopus embryo. In addition, it was also prominent ly expressed in the myotomal muscle. These data suggest that in additi on to motor neurons, the postsynaptic muscle cells can also contribute neuregulin for synaptogenesis. (C) 1998 Elsevier Science B.V. All rig hts reserved.