• OMIM: 167 415
  • MGI: 97492

The paired box protein 8, abbreviated PAX8, is a protein, as a transcription factor which controls, inter alia, the transcription of certain genes in the thyroid. The PAX8 -encoding gene belongs to the family of Pax genes. PAX8 has been proven not only in humans but also in a variety of animal species.

Structure and Function

The human 450 amino acid long, located in the nucleocapsid protein contains in its amino acid sequence, a 127 amino acid long Paireddomäne, can bind on the PAX8 to specific DNA sequence portions and a partial homeodomain. In the thyroid PAX8 controlled in conjunction with TTF1 transcription of thyroglobulin, thyroid peroxidase, and the sodium - iodide symporter.

PAX8 plays an important role not only in the adult organism, but also during the organogenesis of the thyroid gland, and kidney. In the embryo is PAX8 in the developing thyroid, from the earliest system to the differentiated organ, active in various stages of development of the kidney, including pronephros and mesonephros, and the nervous system.

In knockout mice, in which PAX8 is inactive, missing in the thyroid thyroxine -producing follicular epithelial cells; the animals die soon after birth, if they no thyroxine is injected. A number of human genetic studies on a link between the innate hypothyroidism and mutations in the PAX8 gene found so far only isolated cases.

In knockout mice, in which both PAX8 and the like PAX2 is inactive, not only the thyroid is concerned, it also lacks the pronephros.


PAX8 the gene encoding the protein PAX8 part, within the family of Pax genes for Pax2/5/8-Gruppe to the mammalian two paralogous genes PAX2 and PAX5 count. From this group is only PAX8 in thyroid active, while in the developing kidney PAX2 and PAX8 are expressed together and there seems to have partially redundant functions.

The Pax2/5/8-Gruppe was originally identified in the house mouse, but now present in a variety of species of animals with two sides up to the lancelet and the sea squirts. In lancelets AmphiPax2/5/8 is also active in Endostyl, an organ that is homologous to the thyroid of vertebrates.