Members of the Pax family of transcription factors contain a paired box DNA binding domain and may or may not contain a paired-type homeodomain and/or octapeptide region. Nine Pax genes have been identified in mammals and are divided into four subgroups based on the sequence elements present. Pax genes play a variety of roles during embryogenesis, regulating cell-lineage specification, proliferation, migration, and survival of diverse cell and tissue types. Several of the Pax genes are also expressed in cancers and serve as tumor markers.
Pax3 is expressed during early neurogenesis and in developing muscle. Pax3 plays a key role in normal neural development and also works together with Pax7 to regulate the formation and growth of skeletal muscle. Pax3 expression has been observed in melanocyte stem cells where it appears to act as an initiator of melanocyte stem cell differentiation. Pax3 is also implicated melanoma cell survival. There is 98% homology between human and mouse Pax3.