The perplexing multifunctionality of janusin, a tenascin-related molecule

The extracellular matrix glycoprotein janusin, closely related to tenascin in its repeated motifs of epidermal growth factor, fibronectin type III, and fibrinogen-like domains, displays in vitro a broad spectrum of functional diversity. Synthesized by oligodendrocytes and subpopulations of neurons at late developmental stages in the rodent central nervous system, it can be adhesive or antiadhesive, depending on the neural cell type that interacts with it. It promotes neurite outgrowth of some neural cell types, when offered as a uniform culture substrate, but inhibits neurite outgrowth of other neuronal populations. When offered as a sharp substrate boundary in congruence with a permissive substrate, it acts as a barrier for neurite outgrowth. Like tenascin, it can modify the adhesive substrate properties of another extracellular matrix glycoprotein, fibronectin, whereby the smaller, 160 kD component of janusin exerts its effects by interaction with fibronectin and the 180 kD janusin component functionally modifies the fibronectin receptor via a disialoganglioside receptor. In neurons, the antiadhesive and neurite outgrowth inhibiting signal is mediated by the F3/11 immunoglobulin superfamily recognition molecule. In oligodendrocytes, yet another receptor for janusin mediates adhesion and process formation. A prerequisite for any intracellular response to occur is a transient lock-and-key recognition manifesting itself in short-term binding between the interacting partners. As for tenascin, the different functions exerted by janusin are likely to be encoded in the different domains of the janusin molecule, which can act on different receptors, whereby the receiving cell is able to interpret the cell surface trigger in different ways, depending on the particular cell type involved.(ABSTRACT TRUNCATED AT 250 WORDS)