The extracellular matrix molecule janusin regulates neuronal morphology in a substrate- and culture time-dependent manner.

Janusin is an extracellular matrix glycoprotein with structural homology to tenascin. In search of extracellular matrix components which govern the differentiation of neurons in the central nervous system, we have investigated the influence of janusin on the differentiation of hippocampal neurons in vitro. Janusin coated onto nitrocellulose was a good substrate for attachment of cell bodies and neurite outgrowth after 21 h of culture. Most cells exhibited a polarized morphology with one long major neurite and one or two short minor neurites. When janusin was coated onto a polyornithine-conditioned plastic surface, it increased the polarity of neurons in that the length of major neurites was increased and the length and number of minor neurites were decreased when compared with the control polyornithine-conditioned plastic without janusin. As we have shown before for tenascin, laminin and fibronectin, polarization was preceded by an increase in the number and length of all neurites during the first hours after cell plating. This study therefore adds janusin to the increasing number of extracellular matrix glycoproteins which promote axonal but not dendritic growth.