The ParaHox gene cluster is an array of
homeobox
A homeobox is a Nucleic acid sequence, DNA sequence, around 180 base pairs long, that regulates large-scale anatomical features in the early stages of embryonic development. Mutations in a homeobox may change large-scale anatomical features of ...
genes (involved in
morphogenesis, the regulation of patterns of anatomical development) from the
Gsx,
Xlox (
Pdx) and
Cdx gene families.
Regulatory gene cluster
These genes were first shown to be arranged into a physically-linked chromosomal cluster in
amphioxus, an
invertebrate
Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...
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
Homeobox protein CDX-1 is a protein in humans that is encoded by the ''CDX1'' gene. CDX-1 is expressed in the developing endoderm and its expression persists in the intestine throughout adulthood. CDX-1 protein expression varies along the intesti ...
,
CDX2,
CDX4), of which three genes (
GSX1,
PDX1 (=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 113 million base pairs (the building material of DNA) and represents between 3.5 and 4% of the total DNA i ...
. 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
Hox genes, a subset of homeobox, homeobox genes, are a gene cluster, group of related genes that Evolutionary developmental biology, specify regions of the body plan of an embryo along the craniocaudal axis, head-tail axis of animals. Hox protein ...
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 to specify or pattern the through-gut, with Gsx patterning the mouth, Xlox (=Pdx) patterning the midgut and Cdx marking the anus.][ 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
See also
* ParaHoxozoa
{{Transcription factors and intracellular receptors, g3