Identification and characterization of the promoter for the cytotactin gene

Cytotactin binding: inhibition of stimulated proliferation and intracellular alkalinization in fibroblasts

Cytotactin is an extracellular matrix protein that is dynamically and transiently expressed in a place-dependent fashion during development by glial cells, fibroblasts, and several other cell types. In the present study, the effects of cytotactin on cell proliferation were examined in fibroblastic cells in culture. NIH 3T3 mouse cells plated on tissue culture substrata in the presence of soluble cytotactin remained rounded for longer periods than untreated control cells, similar to their response to cytotactin-coated substrates. These rounding effects could be prevented by pretreatment of the cells with nocodazole, a microtubule-disrupting agent. Cytotactin inhibited the proliferation of fibroblasts in culture in a dose- and time-dependent manner, and this inhibition occurred even after nocodazole treatment. In addition, the presence of cytotactin inhibited proliferation stimulated by growth factors or tumor promoter. These effects on cell growth were accompanied by an early inhibition of the intracellular alkalinization that normally occurs upon mitogenic stimulation by a number of growth-promoting agents. Together these observations suggest that cytotactin is an endogenous cell surface modulatory protein and provide a possible mechanism whereby cytotactin may contribute to pattern formation during development, regeneration, tumorigenesis, and wound healing.

Structure of the human hexabrachion (tenascin) gene

The structure of the gene encoding human hexabrachion (tenascin) has been determined from overlapping clones isolated from a human genomic bacteriophage library. The genomic inserts were characterized by restriction mapping, Southern blot analysis, PCR, and DNA sequencing. The coding region of the hexabrachion gene spans approximately 80 kilobases of DNA and consists of 27 exons separated by 26 introns. The exon-intron structure supports a hypothesis based on the cDNA sequence that the hexabrachion gene is an assembly of DNA modules that are also found elsewhere in the genome. Single exons may encode a module, a portion of a module, or a group of modules. The 15 type III units similar to those found in fibronectin are each encoded either by a single exon or by two exons interrupted by an intron. All type III units known to be spliced out of the smaller forms of the protein are encoded by one exon. The fibrinogen-like domain of 210 amino acids is encoded by five exons. The 14.5 epidermal growth factor-like repeats are all encoded by a single exon.

Cytotactin expression in somites after dorsal neural tube and neural crest ablation in chicken embryos

The spatiotemporal expression of the extracellular matrix protein cytotactin/tenascin during somitogenesis suggests that it plays a role in the morphogenetic events that give rise to the pattern of neural crest (NC) development. In the present study, the spatial distribution and molecular forms of cytotactin in somites were examined using in situ hybridization, Western blotting, and immunohistochemistry during normal development and after injury. In situ hybridization showed that prior to NC cell invasion cytotactin mRNA was restricted to the caudal half of the newly formed epithelial somites. As each epithelial somite matured, giving rise to a sclerotome and dermamyotome, the mRNA was first restricted to the dermamyotome and later restricted to the rostral protion of the sclerotome, consistent with the previously reported protein distribution. Immunocytochemical analysis of the distribution of cytotactin and NC cells in embryos with ablations that removed NC cells, or with simple wounds that left NC cells in place, demonstrated that the presence of NC cells is neither necessary nor sufficient for the correct positioning of cytotactin. Immunoblotting analysis showed that cytotactin synthesized by sclerotomes in the absence of NC cells was of similar molecular mass to that produced in their presence. These findings are in accord with the notion that the abnormalities of cytotactin distribution are related to the wounding process. We conclude that, contrary to the suggestion of Stern et al. [Stern, C. D., Norris, W. E., Bronner-Fraser, M., Carlson, G. J., Faissner, A., Keynes, R. J. & Schachner, M. (1989) Development 107, 309-319], there is no causal link between the presence of NC cells and the distribution and molecular mass of sclerotomal cytotactin.