CLONING AND SEQUENCING OF A 1.3 KB VARIANT OF HUMAN THYROTROPIN RECEPTOR MESSENGER-RNA LACKING THE TRANSMEMBRANE DOMAIN

We amplified human thyroidal cDNA using oligonucleotide primers designed to reveal putative human thyrotropin receptor (hTSHR) mRNA variants encoding the extracellular, ligand-binding domain but lacking the transmembrane domain. Whereas the major 4.3 kb hTSHR mRNA species was not amplified to detectable levels, several shorter products were detected. A strongly amplified 1 kb product was cloned and sequenced. It contained coding sequences at the 5′ end which were colinear with exons 1-8 of the hTSHR gene, encoding most of the extracellular domain. This was followed at the 3′ end by additional coding and noncoding information not present in the 4.3 kb transcript. A probe specific for the 5′ end recognized polyadenylated thyroidal transcripts of 4.3, 1.7, and 1.3 kb, indicating the presence of several hTSHR mRNA variants. A probe specific for the 3′ end recognized only the 1.3 kb transcript. The level of the 1.3 kb variant (hTSHR-v1.3 mRNA) was about half that of the 4.3 kb hTSHR mRNA and twice that of the 1.7 kb variant. The presence of a thyroidal mRNA encoding both the signal peptide and ligand-binding region of the hTSHR, but not the seven transmembrane helices, provides the potential to produce soluble receptors which could play important roles in thyroid physiology and/or autoimmune thyroid disease. © 1992.