Evidence from neuron/lymphoma heterokaryons for a common trans-acting factor suppressing Thy-1 expression.

We have investigated the tissue specificity of a trans-acting regulatory factor observed to suppress Thy-1 expression during normal neuronal differentiation. Heterokaryons were constructed between Thy-1.1+ expressing mouse T cell lymphoma cells and Thy-1.2- mouse sensory neurons and their surface phenotypes determined by immunofluorescence histochemistry 16 h after fusion. Thy-1.1 expression was observed to be specifically suppressed in such heterokaryons whilst the expression of the lymphoma cell surface marker, Ly-1, was not altered. As the nuclei did not fuse in the heterokaryons, it appears that the developmentally regulated diffusible suppressor factor active in sensory neurons is not tissue specific and can down-regulate Thy-1 expression in lymphoma cells. We also report the suppression of the H-2Kk surface antigen in heterokaryons by a similar but independent regulatory mechanism.