Genetic deletion of sonic hedgehog causes hemiagenesis and ectopic development of the thyroid in mouse.

• Thyroid dysgenesis encountered in 85% of patients with congenital hypothyroidism is a morphologically heterogeneous condition with primarily unknown pathogenesis. Here we identify sonic hedgehog (Shh) as a novel regulator of thyroid development. In Shh knockout mice the thyroid primordium is correctly specified in the pharyngeal endoderm, but budding and dislocation are slightly delayed. In late development the thyroid fails to form a bilobed gland. Instead a single thyroid mass is found unilaterally and mostly to the left of the midline. Thyroid-specific transcription factors (TTF-1 and TTF-2) and thyroglobulin are expressed indicating terminal differentiation. Strikingly, TTF-1- and TTF-2-positive cells aberrantly develop in the presumptive trachea of Shh-/- embryos. The ectopic tissue buds ventrolaterally into the adjacent mesenchyme, and less extensively into the tracheal lumen, forming follicle-like structures that accumulate thyroglobulin. Shh mRNA is not expressed in the thyroid precursor cells at any developmental stage. The results indicate that Shh signaling indirectly governs the symmetric bilobation of the thyroid during late organogenesis. Shh also seems to repress inappropriate thyroid differentiation in nonthyroid embryonic tissues. This study provides clues to the molecular mechanisms that might be dysregulated in thyroid hemiagenesis and development of ectopic thyroid tissue outside the thyroglossal duct.

Nyckelord

Animals

Cell Differentiation

Epithelium

pathology

Gene Deletion

Hedgehog Proteins

Immunohistochemistry

In Situ Hybridization

Mice

Mice

Transgenic

RNA

Messenger

metabolism

Signal Transduction

Thyroglobulin

metabolism

Thyroid Gland

metabolism

pathology

Time Factors

Trachea

pathology

Trans-Activators

metabolism

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)