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Available protein structures:
Pfam	structures / ECOD
PDB	RCSB PDB; PDBe; PDBj
PDBsum	structure summary

Paired domain
Paired domain
	PAX5 bound to DNA (PDB: 1mdm).
Identifiers
Symbol	PAX
Pfam	PF00292
InterPro	IPR001523
PROSITE	PDOC00034
CATH	1pdn
SCOP2	1pdn / SCOPe / SUPFAM
CDD	cd00131
Pfam
Available protein structures:
Pfam	structures / ECOD
PDB	RCSB PDB; PDBe; PDBj
PDBsum	structure summary

In evolutionary developmental biology, Paired box (Pax) genes are a family of genes coding for tissue specific transcription factors containing an N-terminal paired domain and usually a partial, or in the case of four family members (PAX3, PAX4, PAX6 and PAX7),^[1] a complete homeodomain to the C-terminus. An octapeptide as well as a Pro-Ser-Thr-rich C terminus may also be present.^[2] 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.

The paired domain was initially described in 1987 as the "paired box" in the Drosophila protein paired (prd; P06601).^[3]^[4]

Groups

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).

Two more families, Pox-neuro and Pax-α/β, exist in basal bilaterian species.^[5]^[6] Orthologous genes exist throughout the Metazoa, including extensive study of the ectopic expression in Drosophila using murine Pax6.^[7] The two rounds of whole-genome duplications in vertebrate evolution is responsible for the creation of as many as 4 paralogs for each Pax protein.^[8]

Members

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. In the mouse Pax1 mutation has been linked to undulated mutant suffering from skeletal malformations.^[9]
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.^[10]
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. PAX3 is frequently expressed in melanomas^[11] and contributes to tumor cell survival.^[12]
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. Knockout mice lacking Pax4 expression fail to develop insulin-producing cells.^[13] Pax4 undergoes mutual reciprocal interaction with the transcription factor Arx to endow pancreatic endocrine cells with insulin and glucagon cells respectively^[14]
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 (eyeless) 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.^[15]
PAX7 has been possibly associated with myogenesis. It transcribes a protein of 520 amino acids from 8 exons and 2,260bps in humans. PAX7 directs postnatal renewal and propagation of myogenic satellite cells but not for the specification.^[16]
PAX8 has been associated with thyroid specific expression. It transcribes a protein of 451 amino acids from 11 exons and 2,526bps in humans. Pax8 loss-of-function mutant mice lack follicular cells of the thyroid gland.^[17]
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.

References

^ Chi, N; Epstein, JA (January 2002). "Getting your Pax straight: Pax proteins in development and disease". Trends in Genetics. 18 (1): 41–7. doi:10.1016/s0168-9525(01)02594-x. PMID 11750700.
^ Eberhard, D; Jiménez, G; Heavey, B; Busslinger, M (15 May 2000). "Transcriptional repression by Pax5 (BSAP) through interaction with corepressors of the Groucho family". The EMBO Journal. 19 (10): 2292–303. doi:10.1093/emboj/19.10.2292. PMC 384353. PMID 10811620.
^ Bopp, D; Burri, M; Baumgartner, S; Frigerio, G; Noll, M (26 December 1986). "Conservation of a large protein domain in the segmentation gene paired and in functionally related genes of Drosophila". Cell. 47 (6): 1033–40. doi:10.1016/0092-8674(86)90818-4. PMID 2877747. S2CID 21943167.
^ Baumgartner, S; Bopp, D; Burri, M; Noll, M (December 1987). "Structure of two genes at the gooseberry locus related to the paired gene and their spatial expression during Drosophila embryogenesis". Genes & Development. 1 (10): 1247–67. doi:10.1101/gad.1.10.1247. PMID 3123319.
^ Navet, S; Buresi, A; Baratte, S; Andouche, A; Bonnaud-Ponticelli, L; Bassaglia, Y (2017). "The Pax gene family: Highlights from cephalopods". PLOS ONE. 12 (3): e0172719. Bibcode:2017PLoSO..1272719N. doi:10.1371/journal.pone.0172719. PMC 5333810. PMID 28253300.
^ Franke, FA; Schumann, I; Hering, L; Mayer, G (2015). "Phylogenetic analysis and expression patterns of Pax genes in the onychophoran Euperipatoides rowelli reveal a novel bilaterian Pax subfamily". Evolution & Development. 17 (1): 3–20. doi:10.1111/ede.12110. PMID 25627710. S2CID 205095304.
^ Gehring WJ, Ikeo K (September 1999). "Pax 6: mastering eye morphogenesis and eye evolution". Trends in Genetics. 15 (9): 371–7. doi:10.1016/S0168-9525(99)01776-X. PMID 10461206.
^ Ravi V, Bhatia S, Gautier P, Loosli F, Tay BH, Tay A, Murdoch E, Coutinho P, van Heyningen V, Brenner S, Venkatesh B, Kleinjan DA (2013). "Sequencing of Pax6 loci from the elephant shark reveals a family of Pax6 genes in vertebrate genomes, forged by ancient duplications and divergences". PLOS Genetics. 9 (1): e1003177. doi:10.1371/journal.pgen.1003177. PMC 3554528. PMID 23359656.
^ Balling et al., 1988
^ Online Mendelian Inheritance in Man (OMIM): 167409
^ Medic S, Ziman M (April 2010). Soyer, H. Peter (ed.). "PAX3 Expression in Normal Skin Melanocytes and Melanocytic Lesions (Naevi and Melanomas)". PLOS ONE. 5 (4): e9977. Bibcode:2010PLoSO...5.9977M. doi:10.1371/journal.pone.0009977. PMC 2858648. PMID 20421967.
^ Scholl FA, Kamarashev J, Murmann OV, Geertsen R, Dummer R, Schäfer BW (Feb 2001). "PAX3 is expressed in human melanomas and contributes to tumor cell survival". Cancer Res. 61 (3): 823–6. PMID 11221862.
^ Sosa-Pineda et al., 1997
^ Collombat et al, 2003
^ Walter and Gruss, 1991
^ Oustanina, S; et al. (2004). "PAX7 directs postnatal renewal and propagation of myogenic satellite cells but not their specification". The EMBO Journal. 23 (16): 3430–3439. doi:10.1038/sj.emboj.7600346. PMC 514519. PMID 15282552.
^ Mansouri et al.,1998

^[1]==Further reading==

Zuker, Charles S. (August 1994). "On the evolution of eyes: would you like it simple or compound?". Science. 265 (5173): 742–3. Bibcode:1994Sci...265..742Z. doi:10.1126/science.8047881. PMID 8047881.
Quiring, Rebecca; Walldorf, Uwe; Kloter U; Gehring WJ (August 1994). "Homology of the eyeless gene of Drosophila to the small eye gene in mice and Aniridia in humans". Science. 265 (5173): 785–9. Bibcode:1994Sci...265..785Q. doi:10.1126/science.7914031. PMID 7914031.