PAX9 Antibody #8739

Paired box (PAX) proteins are a family of transcription factors that play important and diverse roles in animal development (1). Nine PAX proteins (PAX1-9) have been described in humans and other mammals. They are defined by the presence of an amino-terminal "paired" domain, consisting of two helix-turn-helix motifs, with DNA binding activity (2). PAX proteins are classified into four structurally distinct subgroups (I-IV) based on the absence or presence of a carboxy-terminal homeodomain and a central octapeptide region. Subgroup I (PAX1 and 9) contains the octapeptide but lacks the homeodomain; subgroup II (PAX2, 5, and 8) contains the octapeptide and a truncated homeodomain; subgroup III (PAX3 and 7) contains the octapeptide and a complete homeodomain; and subgroup IV (PAX4 and 6) contains a complete homeodomain but lacks the octapeptide region (2). PAX proteins play critically important roles in development by regulating transcriptional networks responsible for embryonic patterning and organogenesis (3); a subset of PAX proteins also maintain functional importance during postnatal development (4). Research studies have implicated genetic mutations that result in aberrant expression of PAX genes in a number of cancer subtypes (1-3), with members of subgroups II and III identified as potential mediators of tumor progression (2).
PAX9 is expressed in pharyngeal arch mesenchyme (5,6), and is essential for embryonic development of the teeth and other pharyngeal arch derivatives (5,7). In mice, deletion of PAX9 results in an absence of structures derived from the pharyngeal pouches (e.g. thymus, parathyroid glands) (5), while in humans, PAX9 mutations are frequently associated with congenital tooth agenesis syndromes such as oligodontia and hypodontia (8,9). PAX9 appears to interact with other transcription factors (e.g. MSX1) to regulate the expression of BMP-family proteins (e.g. BMP4) that orchestrate pharyngeal arch development (10,11). Increased expression of PAX9, resulting from amplification at the PAX9 locus, has also been linked to an increased incidence of lung cancer (12).