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Normal Thyroid Structure and Function in Rhophilin 2-Deficient Mice

Jens Behrends ,^1,, Serge Clément,^1, Bernard Pajak,² Viviane Pohl,¹ Carine Maenhaut,¹ Jacques E. Dumont,¹ and Stéphane Schurmans^1*

Institut de Recherches Interdisciplinaires en Biologie Humaine et Moléculaire, Faculté de Médecine,¹ Laboratoire de Physiologie Animale, Faculté des Sciences, Institut de Biologie et de Médecine Moléculaires, Université Libre de Bruxelles, Gosselies, Belgium²

Received 23 July 2004/ Returned for modification 24 August 2004/ Accepted 15 December 2004

Rhophilin 2 is a Rho GTPase binding protein initially isolated by differential screening of a chronically thyrotropin (TSH)-stimulated dog thyroid cDNA library. In thyroid cell culture, expression of rhophilin 2 mRNA and protein is enhanced following TSH stimulation of the cyclic AMP (cAMP) transduction cascade. Yeast two-hybrid screening and coimmunoprecipitation have revealed that the GTP-bound form of RhoB and components of the cytoskeleton are protein partners of rhophilin 2. These results led us to suggest that rhophilin 2 could play an important role downstream of RhoB in the control of endocytosis during the thyroid secretory process which follows stimulation of the TSH/cAMP pathway. To validate this hypothesis, we generated rhophilin 2-deficient mice and analyzed their thyroid structure and function. Mice lacking rhophilin 2 develop normally, have normal life spans, and are fertile. They have no visible goiter and no obvious clinical signs of hyper- or hypothyroidism. The morphology of thyroid cells and follicles in these mice were normal, as were the different biological tests performed to investigate thyroid function. Our results indicate that rhophilin 2 does not play an essential role in thyroid physiology.

J.B. and S.C. contributed equally to this work.

Present address: Medizinische Hochschule Hannover, Department of Gastroenterology, Hepatology and Endocrinology, 30623 Hannover, Germany.