ZEBRAFISH TENASCIN-W, A NEW MEMBER OF THE TENASCIN FAMILY

A cDNA clone encoding tenascin-W, a novel member of the tenascin famil y, was isolated from a 20- to 28-h postfertilization (hpf) zebrafish c DNA library on the basis of the conserved epidermal growth factor-like domains represented in all tenascin molecules. An open reading frame of 2796 base pairs encodes a mature protein consisting of heptad repea ts, a cysteine-rich amino terminal region, 3.5 epidermal growth factor -like repeats, five fibronectin type III homologous repeats, and a dom ain homologous to fibrinogen. These domains are the typical modular el ements of molecules of the tenascin family. Sequence comparison demons trated that TN-W shares homologies with the members of the tenascin fa mily but is not a species homolog of any identified tenascin. The expr ession pattern of tn-w was analyzed by in situ hybridization in 1-day- old embryos, in 3-day-old larvae, and in juvenile zebrafish. At 24-25 hpf, tn-w mRNA was expressed in the lateral plate mesoderm, most consp icuously in the presumptive sclerotome. Migrating cells of sclerotomal and neural crest origins also showed high levels of expression. At 3 days, expression by sclerotomal and neural crest cells continued to be observed while expression in the semitic mesoderm was decreased. In j uvenile fish, tn-w was expressed weakly by cells in the myosepta and, more strongly, by presumably nonneuronal cells in the dorsal root gang lia. In these tissues and at the same developmental stages, the expres sion of tn-w partially overlapped with the distribution of tn-c mRNA. In addition, tit-e was expressed in the central nervous system (CNS) a nd in the axial mesoderm, neither of which expressed tn-w at any of th e age stages examined. The expression pattern of tn-w suggests an invo lvement in neural crest and sclerotome cell migration and in the forma tion of the skeleton. Similar and possibly overlapping functions could also be performed by tn-c, which appears to have additional functions during the development of the CNS. (C) 1998 John Wiley & Sons, Inc.