LACK OF EVIDENCE SUPPORTING THE PRESENCE OF MESSENGER-RNA FOR THE THYROTROPIN RECEPTOR IN EXTRA-OCULAR MUSCLE

The search for autoantigenic targets in thyroid associated ophthalmopa thy (TAO) and a possible link with the thyroid continues. Several auth ors have presented data suggesting that extrathyroidal tissues, e.g. e xtraocular muscle (EOM), may contain a functional thyrotropin receptor (TSH-R). We have applied Northern blotting and PCR amplification in a n attempt to demonstrate the mRNA for the TSH-R in EOM, which although predominantly composed of muscle, may contain a significant proportio n of fibroblasts. In Northern blots of poly (A) mRNA of normal human t hyroid, EOM and skeletal muscle (SM) probed with a p32 labeled hTSH-R cDNA, transcripts of 4.6 and 4.4 kb were observed only in the thyroid. PCR amplification was performed on thyroid and EOM cDNAs using pairs of primers designed to amplify exons 1-->9, the extracellular domain ( ECD), and exon 10, the intracellular domain (ICD). Both the ECD and IC D were amplified from a thyroidal cDNA library but only the ICD in the EOM cDNA library, this probably being due to the inevitable contamina tion with genomic DNA. These results do not support the hypothesis tha t the TSH receptor, as such, would be an autoantigen of EOM involved i n TAO.