Abstract
Thyroid hormone receptors (TR) mediate the action of thyroid hormones. Genetic studies
revealed that the individual TR isoforms possess different functions. In the present
paper we studied the expression of the isoforms TRα1 and TRβ1 in the murine pancreatic
islet. TRα1 and TRβ1 mRNA transcripts and proteins were detected in islets using reverse
transcription-polymerase chain reaction and Western blotting analyses, respectively.
In immunohistochemical studies individual cells in the periphery of islets were labelled
using an anti-TRα1 antibody. No labelled cells were detected in the exocrine pancreas.
A similar staining pattern was obtained with an anti-glucagon antibody, but not with
an anti-insulin antibody, which suggests that TRα1 is mainly expressed in α-cells.
In order to address a potential function of TRα1 in this cell type, the regulation
of glucagon gene expression by triiodothyronine was studied in a glucagon-producing
cell line by Northern blot analysis and transient transfection assays using glucagon
promoter luciferase fusion gene constructs. In these assays, triiodothyronine did
not regulate the glucagon mRNA level or the glucagon promoter activity. The predominant
localization of TRα1 in pancreatic α-cells suggests that this receptor isoform mediates
a specific, yet unknown, function of thyroid hormones in this cell type.
Key words
Thyroid hormone - receptor - pancreas - diabetes mellitus - glucagon
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Dr. Andreas Zinke
Clinic of Nuclear Medicine
Fleischmannstraße 42
17487 Greifswald
Germany
Phone: + 493834866983
Fax: + 49 38 34 86 69 82
Email: zinke-an@uni-greifswald.de
