DIFFERENTIAL EXPRESSION OF TRIIODOTHYRONINE RECEPTORS IN SCHWANNOMA AND NEUROFIBROMA - ROLE OF SCHWANN CELL-AXON INTERACTION

Regulation of gene expression in Schwann cells may be determined, at l east in part, by the interaction of these cells with axons. Two periph eral nerve tumors, neurofibroma and schwannoma, represent good tools f or studying Schwann cell activity in the presence or absence of axon a ction. In the present work we studied the expression of triiodothyroni ne receptors (T(3)R) by Schwann cells in these two tumors and also in adult normal sciatic nerve. Confirming the results of the histological examination, immunostaining of the neurofilaments showed the presence of fascicles of scattered axons in all neurofibroma sections studied. In these neurofibromas, Schwann cells did not express T(3)R immunorea ctivity. Furthermore, in adult normal sciatic nerve, Schwann cells whi ch ensheathed axons were devoid of any T(3)R expression. In contrast, in schwannoma, the complete absence of axons was demonstrated by the l ack of neurofilament immunostaining. Here, Schwann cells deprived of a xonal interaction displayed clear T(3)R immunoreactivity. In schwannom a cell cultures, Schwann cells continued to express T(3)R, even in cul tures treated with medium that had been conditioned with rat sensory n eurons. On the basis of these results, we suggest that, beside the pos sible regulatory mechanisms for T(3)R, the synthesis of T(3)R is regul ated, at least in part, by Schwann cell-axon interaction.