Paired box (Pax) genes are a family of tissue specific transcription factors containing a PAIRED domain and usually a partial or complete homeodomain. An octapeptide may also be present. Pax proteins are important in early animal development for the specification of specific tissues, as well as during epimorphic limb regeneration in animals capable of such.
Within the mammalian family, there are four well defined groups of Pax genes.
Pax group 1 (Pax 1 and 9),
Pax group 2 (Pax 2, 5 and 8),
Pax group 3 (Pax 3 and 7) and
Pax group 4 (Pax 4 and 6).
Orthologous genes exist throughout the Metazoa, including extensive study of the ectopic expression in Drosophila using murine Pax6.
PAX1 has been identified in mice with the development of vertebrate and embryo segmentation, and some evidence this is also true in humans. It transcribes a 440 amino acid protein from 4 exons and 1,323bps in humans.
PAX2 has been identified with kidney and optic nerve development. It transcribes a 417 amino acid protein from 11 exons and 4,261 bps in humans. Mutation of PAX2 in humans has been associated with renal-coloboma syndrome as well as oligomeganephronia.
PAX3 has been identified with ear, eye and facial development. It transcribes a 479 amino acid protein in humans. Mutations in it can cause Waardenburg syndrome.
PAX4 has been identified with pancreatic islet beta cells. It transcribes a 350 amino acid protein from 9 exons and 2,010 bps in humans.
PAX5 has been identified with neural and spermatogenesis development and b-cell differentiation. It transcribes a 391 amino acid protein from 10 exons and 3,644bps in humans.
PAX6 is the most researched and appears throughout the literature as a "master control" gene for the development of eyes and sensory organs, certain neural and epidermal tissues as well as other homologous structures, usually derived from ectodermal tissues.
PAX7 has been possibly associated with myogenesis. It transcribes a protein of 520 amino acids from 8 exons and 2,260bps in humans. PAX7 is required for the developmental specification of satellite cells in skeletal muscle.
PAX8 has been associated with thyroid specific expression. It transcribes a protein of 451 amino acids from 11 exons and 2,526bps in humans.
PAX9 has found to be associated with a number of organ and other skeletal developments, particularly teeth. It transcribes a protein of 341 amino acids from 4 exons and 1,644bps in humans.