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Molecular Genetics of Thyroid Gland Development


The discovery of transcription factors, which regulate the expression of follicular cell-specific genes in the mature thyroid and are also expressed in the thyroid primordium, offered a useful tool to explore the genetic basis of the developmental process of the thyroid gland. At E8.5 epithelial cells fated to become thyroid follicular cells are unequivocally individualized in the endodermal layer of the primitive pharynx. These cells are characterized by the expression of Nkx2-1/Ttf-1,[100] Foxe1,[126] Pax8,[127] and Hhex.[128]Although these transcription factors are also expressed in other embryonic tissues, the coexpression of all four is only seen in the presumptive thyroid anlage when the thickening of proliferating cells appears in the midline of the floor of the primitive pharynx. When the thyroid diverticulum forms and begins its migration, only the thyroid primordium still expresses Nkx2-1/Ttf-1, Foxe1, Pax8 and Hhex, while the …