25 Facts About Hox genes

In larvae with gradual metamorphosis the Hox genes are activated in tissues of the larval body, generally in the trunk region, that will be maintained through metamorphosis.

In larvae with complete metamorphosis the Hox genes are mainly expressed in juvenile rudiments and are absent in the transient larval tissues.

An analogy for the Hox genes can be made to the role of a play director who calls which scene the actors should carry out next.

Protein product of each Hox genes gene is a transcription factor.

Each Hox genes gene contains a well-conserved DNA sequence known as the homeobox, of which the term "Hox genes" was originally a contraction.

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However, in current usage the term Hox is no longer equivalent to homeobox, because Hox genes are not the only genes to possess a homeobox sequence; for instance, humans have over 200 homeobox genes, of which 39 are Hox genes.

Hox genes are thus a subset of the homeobox transcription factor genes.

Barrett's esophagus is the result of altered Hox genes coding and is a precursor to esophageal cancer.

The Hox genes, being a subset of homeobox genes, arose more recently in evolution within the animal kingdom or Metazoa.

In bilateria, Hox genes are often arranged in gene clusters, although there are many exceptions where the genes have been separated by chromosomal rearrangements.

In most bilaterian animals, Hox genes are expressed in staggered domains along the head-to-tail axis of the embryo, suggesting that their role in specifying position is a shared, ancient feature.

So, despite having a last common ancestor that lived over 550 million years ago, the chicken and fly version of the same Hox gene are similar enough to target the same downstream genes in flies.

Hox genes act at many levels within developmental gene hierarchies: at the "executive" level they regulate genes that in turn regulate large networks of other genes.

Segmentation involves such processes as morphogenesis, the tight association of groups of cells with similar fates, the sculpting of structures and segment boundaries via programmed cell death, and the movement of cells from where they are first born to where they will ultimately function, so it is not surprising that the target genes of Hox genes promote cell division, cell adhesion, apoptosis, and cell migration.

The sequence bound by the homeodomain of a Hox genes protein is only six nucleotides long, and such a short sequence would be found at random many times throughout the genome, far more than the number of actual functional sites.

Just as Hox genes regulate realisator genes, they are in turn regulated themselves by other genes.

In Drosophila and some insects, Hox genes are regulated by gap genes and pair-rule genes, which are in their turn regulated by maternally-supplied mRNA.

MicroRNA strands located in Hox clusters have been shown to inhibit more anterior hox genes, possibly to better fine tune its expression pattern.

Genes in the 3' ends of Hox clusters are induced by retinoic acid resulting in expression domains that extend more anteriorly in the body compared to 5' Hox genes that are not induced by retinoic acid resulting in expression domains that remain more posterior.

In some organisms, especially vertebrates, the various Hox genes are situated very close to one another on the chromosome in groups or clusters.

Vertebrates do have HOX genes that are homologous to those of the fly as it is one of the most highly conserved genes, but the location is different.

In flies, one gene can be mutated, resulting in a haltere, something fundamental for them to be able to fly, being transformed into a wing, or an antenna turning into a leg; in the mouse, two to four Hox genes must be simultaneously removed to get a similar complete transformation.

The Hox genes are active in the lower back, where the vertebrae don't grow ribs, and inactive in the mid-back, allowing ribs to be formed.

Six Hox genes are dispersed in the genome of Caenorhabditis elegans, a roundworm.

Hox genes are so named because mutations in them cause homeotic transformations.

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