title: Early thyroid development requires a Tbx1-Fgf8 pathway.
abstract: The thyroid develops within the pharyngeal apparatus from endodermally-derived cells. The many derivatives of the pharyngeal apparatus develop at similar times and sometimes from common cell types, explaining why many syndromic disorders express multiple birth defects affecting different structures that share a common pharyngeal origin. Thus, different derivatives may share common genetic networks during their development. Tbx1, the major gene associated with DiGeorge syndrome, is a key player in the global development of the pharyngeal apparatus, being required for virtually all its derivatives, including the thyroid. Here we show that Tbx1 regulates the size of the early thyroid primordium through its expression in the adjacent mesoderm. Because Tbx1 regulates the expression of Fgf8 in the mesoderm, we postulated that Fgf8 mediates critical Tbx1-dependent interactions between mesodermal cells and endodermal thyrocyte progenitors. Indeed, conditional ablation of Fgf8 in Tbx1-expressing cells caused an early thyroid phenotype similar to that of Tbx1 mutant mice. In addition, expression of an Fgf8 cDNA in the Tbx1 domain rescued the early size defect of the thyroid primordium in Tbx1 mutants. Thus, we have established that a Tbx1->Fgf8 pathway in the pharyngeal mesoderm is a key size regulator of mammalian thyroid.
authors.affiliation: Telethon Institute of Genetics and Medicine, and University Federico II, Naples, Italy.
authors.forename: Gabriella
authors.initials: G
authors.lastname: Lania
authors.forename: Zhen
authors.initials: Z
authors.lastname: Zhang
authors.forename: Tuong
authors.initials: T
authors.lastname: Huynh
authors.forename: Cinzia
authors.initials: C
authors.lastname: Caprio
authors.forename: Anne M
authors.initials: AM
authors.lastname: Moon
authors.forename: Francesca
authors.initials: F
authors.lastname: Vitelli
authors.forename: Antonio
authors.initials: A
authors.lastname: Baldini
mesh_terms: D000818:Animals; D003433:Crosses, Genetic; D004622:Embryo, Mammalian; D051524:Fibroblast Growth Factor 8 / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008648:Mesoderm / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020825:T-Box Domain Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D013961:Thyroid Gland / Q000196:embryology* / Q000378:metabolism / Q000502:physiology*
chemical_list: C496457:Fgf8 protein, mouse; D020825:T-Box Domain Proteins; C491573:Tbx1 protein, mouse; D051524:Fibroblast Growth Factor 8