Perturbed thyroid morphology and transient hypothyroidism symptoms in Hoxa5 mutant mice.

The Hox family of transcriptional regulators has been extensively studied for their role in axial and appendicular patterning. Genetic analyses have also unveiled Hox gene function in organogenesis and postnatal development. A phenotypical survey of the Hoxa5(-/-) mutant mice shows that the surviving mutants display symptoms of hypothyroidism, including transient growth retardation, and delayed eye opening and ear elevation. Thyroid gland morphogenesis initiates normally, but follicle formation and thyroglobulin processing are abnormal at late gestation. The expression of several molecular markers essential for thyroid gland formation and function, namely Nkx2.1, Pax8, and Titf2, is affected in the developing thyroid gland of Hoxa5(-/-) mutants. As a consequence, the expression of thyroid effector genes, including the thyroglobulin and thyroperoxidase genes, is perturbed. Our characterization reveals that the loss of Hoxa5 function transiently affects thyroid development in a non-cell autonomous manner.