ParaHox

Regulatory gene cluster

These genes were first shown to be arranged into a physically-linked chromosomal cluster in amphioxus, an invertebrate with a single member of each of the three gene families. All the ParaHox genes in the amphioxus genome are therefore in the ParaHox gene cluster. In contrast, the human genome has six ParaHox genes (GSX1, GSX2, PDX1, CDX1, CDX2, CDX4), of which three genes (GSX1, PDX1 (=IPF1), CDX2) are physically linked to form a human ParaHox gene cluster on chromosome 13. Mice have a homologous ParaHox gene cluster on chromosome 5. The other three human ParaHox genes are remnants from duplicated ParaHox gene clusters that were generated in the 2R genome duplications at the base of vertebrate evolution. Some vertebrates, notably chondrichthyan fish and coelacanths, have retained an additional ParaHox gene (PDX2).

The ParaHox gene cluster has been proposed to be a paralogue, or evolutionary sister, of the Hox gene cluster; It has been suggested that an ancient role of the ParaHox gene cluster in bilaterians was to specify or pattern the through-gut, with Gsx patterning the mouth, Xlox (=Pdx) patterning the midgut and Cdx marking the anus. Gene expression and functional data lends tentative support to this hypothesis, although in many animals the roles of the genes have changed in evolution, notably the Gsx gene family which plays a role in brain (not foregut) development in vertebrates.

References

References

1. Brooke, N.M.. (1998). "The ParaHox gene cluster is an evolutionary sister of the Hox gene cluster.". Nature.
2. Ferrier, DE. (Oct 25, 2005). "The chordate ParaHox cluster.". Current Biology.
3. (2000-09-01). "Evidence for 14 homeobox gene clusters in human genome ancestry". Current Biology.
4. Mulley, J. F.. (11 May 2010). "Parallel Retention of Pdx2 Genes in Cartilaginous Fish and Coelacanths". Molecular Biology and Evolution.
5. Hui, J. (2008). "Do cnidarians have a ParaHox cluster? Analysis of synteny around a Nematostella homeobox gene cluster". Evolution & Development.
6. Holland, P. W. H.. (31 July 2001). "Beyond the Hox: how widespread is homeobox gene clustering?". Journal of Anatomy.
7. Holland, P. W. H.. (1 January 2012). "Evolution of homeobox genes". Wiley Interdisciplinary Reviews: Developmental Biology.
8. Samadi, Leyli. (1 January 2010). "Conservation of ParaHox genes' function in patterning of the digestive tract of the marine gastropod Gibbula varia". BMC Developmental Biology.
9. Pei, Z. (Jan 25, 2011). "Homeobox genes Gsx1 and Gsx2 differentially regulate telencephalic progenitor maturation.". Proceedings of the National Academy of Sciences of the United States of America.