The ParaHox gene cluster is an array of

homeobox A homeobox is a DNA sequence, around 180 base pairs long, that regulates large-scale anatomical features in the early stages of embryonic development. For instance, mutations in a homeobox may change large-scale anatomical features of the full- ...

genes (involved in

morphogenesis Morphogenesis (from the Greek ''morphê'' shape and ''genesis'' creation, literally "the generation of form") is the biological process that causes a cell, tissue or organism to develop its shape. It is one of three fundamental aspects of devel ...

, the regulation of patterns of anatomical development) from the Gsx,

Xlox PDX1 (pancreatic and duodenal homeobox 1), also known as insulin promoter factor 1, is a transcription factor in the ParaHox gene cluster.Brooke, N. M., Garcia-Fernàndez, J., & Holland, P. W. (1998). The ParaHox gene cluster is an evolutionary si ...

( Pdx) and Cdx gene families.

Regulatory gene cluster

These genes were first shown to be arranged into a physically-linked chromosomal cluster in

amphioxus The lancelets ( or ), also known as amphioxi (singular: amphioxus ), consist of some 30 to 35 species of "fish-like" benthic filter feeding chordates in the order Amphioxiformes. They are the modern representatives of the subphylum Cephalochorda ...

, an

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

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 GSX may refer to: * Gsx (gene family) * GSX Techedu, a large Chinese online tutoring company * Asurada GSX, a fictional racing car from ''Future GPX Cyber Formula'' * Buick GSX, a muscle car * Gandhi Smarak Road railway station, in Maharashtra, Ind ...

PDX1 PDX1 (pancreatic and duodenal homeobox 1), also known as insulin promoter factor 1, is a transcription factor in the ParaHox gene cluster.Brooke, N. M., Garcia-Fernàndez, J., & Holland, P. W. (1998). The ParaHox gene cluster is an evolutionary si ...

CDX1 Homeobox protein CDX-1 is a protein in humans that is encoded by the ''CDX1'' gene. CDX1 is expressed in the developing endoderm and its expression persists in the intestine throughout adulthood. CDX1 protein expression varies along the intestine, ...

, CDX2, CDX4), of which three genes ( GSX1,

(=IPF1), CDX2) are physically linked to form a human ParaHox gene cluster on

chromosome 13 Chromosome 13 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 13 spans about 114 million base pairs (the building material of DNA) and represents between 3.5 and 4% of the total DNA ...

. Mouse has 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 Polyploidy is a condition in which the cells of an organism have more than one pair of ( homologous) chromosomes. Most species whose cells have nuclei ( eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contain ...

at the base of vertebrate evolution. Some vertebrates, notably

chondrichthyan Chondrichthyes (; ) is a class that contains the cartilaginous fishes that have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fishes'', which have skeletons primarily composed of bone tissue. ...

fish and

coelacanths The coelacanths ( ) are fish belonging to the order Actinistia that includes two extant species in the genus ''Latimeria'': the West Indian Ocean coelacanth (''Latimeria chalumnae''), primarily found near the Comoro Islands off the east coast ...

, 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 Hox genes, a subset of homeobox genes, are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals. Hox proteins encode and specify the characteristics of 'position', ensuring that the cor ...

cluster; the two gene clusters being descendent from a segmental duplication early in animal evolution, preceding the divergence of cnidarians and bilaterian animals. It has been suggested that an ancient role of the ParaHox gene cluster in bilaterians was the 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

Developmental genes and proteins Gene clusters

Regulatory gene cluster

References

See also