Hox genes are a group of related gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

s that determine the basic structure and orientation of an organism.

Hox genes are critical for the proper placement of segment structures

Segmentation (biology)

Segmentation in biology refers to either a type of gastrointestinal motility or the division of some animal and plant body plans into a series of repetitive segments. This article will focus on the segmentation of animal body plans, specifically using the examples of the phyla Arthropoda,...

 of animals during early embryonic development (e.g. legs, antennae, and wings in fruit flies or the different vertebrate ribs in humans).

Hox genes are defined as having -

• a DNA
  DNA
  Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
  
   sequence known as the homeobox
  Homeobox
  A homeobox is a DNA sequence found within genes that are involved in the regulation of patterns of anatomical development in animals, fungi and plants.- Discovery :...
  
  
• their location in gene clusters on the genome
• an expression pattern along the cephalo-caudal (head to tail) axis that corresponds to the relative location of their genes within the Hox gene cluster.

The homeobox

The homeobox is a 180 nucleotide

Nucleotide

Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...

 long DNA sequence that encodes a 60 amino acid long protein domain

Protein domain

A protein domain is a part of protein sequence and structure that can evolve, function, and exist independently of the rest of the protein chain. Each domain forms a compact three-dimensional structure and often can be independently stable and folded. Many proteins consist of several structural...

 known as the homeodomain

Homeodomain fold

The homeodomain fold is a protein structural domain that binds DNA or RNA and is thus commonly found in transcription factors. The fold consists of a 60-amino acid helix-turn-helix structure in which three alpha helices are connected by short loop regions...

.

Hox proteins

The products of Hox genes are known as Hox proteins. Hox proteins are transcription factor

Transcription factor

In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...

s, as they are capable of binding to specific nucleotide sequences on the DNA called enhancers

Enhancer (genetics)

In genetics, an enhancer is a short region of DNA that can be bound with proteins to enhance transcription levels of genes in a gene cluster...

 where they either activate or repress genes. The same Hox protein can act as a repressor at one gene and an activator at another. For example, in flies (Drosophila melanogaster) the protein product of the Hox gene Antennapedia

Antennapedia

Antennapedia is a HOM-C gene first discovered in Drosophila which controls the formation of legs during development. Loss-of-function mutations in the regulatory region of this gene result in the development of the second leg pair into ectopic antennae...

 activates genes that specify the structures of the 2nd thoracic segment, which contains a leg and a wing, and represses genes involved in eye and antenna formation. Thus, legs and wings, but not eyes and antennae, will form wherever the Antennapedia protein is located.
The ability of Hox proteins to bind DNA is conferred by a part of the protein referred to as the homeodomain

Homeodomain fold

The homeodomain fold is a protein structural domain that binds DNA or RNA and is thus commonly found in transcription factors. The fold consists of a 60-amino acid helix-turn-helix structure in which three alpha helices are connected by short loop regions...

.

The homeodomain

The homeodomain is a 60 amino acid long DNA-binding domain (encoded by the homeobox on the DNA). This amino acid sequence folds into a helix-turn-helix

Homeodomain fold

The homeodomain fold is a protein structural domain that binds DNA or RNA and is thus commonly found in transcription factors. The fold consists of a 60-amino acid helix-turn-helix structure in which three alpha helices are connected by short loop regions...

 motif that is stabilized by a third helix.

The consensus polypeptide chain is (typical intron

Intron

An intron is any nucleotide sequence within a gene that is removed by RNA splicing to generate the final mature RNA product of a gene. The term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts. Sequences that are joined together in the final...

 position noted with dashes):

RRRKRTA-YTRYQLLE-LEKEFLF-NRYLTRRRRIELAHSL-NLTERHIKIWFQN-RRMK-WKKEN

The first genes found to encode homeodomain proteins were Drosophila

Drosophila

Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...

developmental control genes, in particular Hom-C genes, from which the name homeobox was derived. However, many homeobox genes are not homeotic gene

Homeotic gene

Hox genes are a group of related genes that determine the basic structure and orientation of an organism.Hox genes are critical for the proper placement of segment structures of animals during early embryonic development Hox genes are a group of related genes that determine the basic structure and...

s; the homeobox is a sequence motif, while "homeotic" is a functional description for genes that scaffold structures or developmental patterns.

Sequence conservation

The homeodomain protein motif is highly conserved across vast evolution

Evolution

Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

ary distances. In addition, homeodomains of individual Hox proteins usually exhibit greater similarity to homeodomains in other species than to proteins encoded by adjacent genes within their own Hox cluster. These two observations led to the suggestions that Hox gene clusters evolved from a single Hox gene via tandem duplication

Gene duplication

Gene duplication is any duplication of a region of DNA that contains a gene; it may occur as an error in homologous recombination, a retrotransposition event, or duplication of an entire chromosome.The second copy of the gene is often free from selective pressure — that is, mutations of it have no...

 and subsequent divergence and that a prototypic Hox gene cluster containing at least seven different Hox genes was present in the common ancestor of all bilaterian animals.

Classification of Hox proteins

Proteins with high degree of sequence similarity are also generally assumed to exhibit a high degree of functional similarity, e.g. Hox proteins with identical homeodomains are assumed to have identical DNA-binding properties (unless additional sequences are known to influence that).
To identify the set of proteins between two different species that are most likely to be most similar in function, classification schemes are used. For Hox proteins, three different classification schemes exist: phylogenetic inference based, synenty based, and sequence similarity based.

The functional equivalence of such a set of Hox proteins can be demonstrated by the fact that a fly can function perfectly well with a chicken Hox protein in place of its own. This means that, despite having a last common ancestor

Most recent common ancestor

In genetics, the most recent common ancestor of any set of organisms is the most recent individual from which all organisms in the group are directly descended...

 that lived over 670 million years ago, a given Hox protein in chickens and the homologous gene in flies are so similar that they can actually take each other's places.

Genes regulated by Hox proteins

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 (like the gene pathway that forms an appendage). They also directly regulate what are called realisator genes or effector genes that act at the bottom of such hierarchies to ultimately form the tissues, structures, and organs of each segment. Segmentation involves such processes as morphogenesis (differentiation of precursor cells into their terminal specialized cells), 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.

Examples of targets

Organism	Target gene	Normal function of target gene	Regulated by
Drosophila	distal-less	activates gene pathway for limb formation	ULTRABITHORAX (represses distal-less)
	distal-less	activates gene pathway for limb formation	ABDOMINAL-A (represses distal-less)
	decapentaplegic	triggers cell shape changes in the gut that are required for normal visceral morphology	ULTRABITHORAX (activates decapentaplegic)
	reaper	Apoptosis: localized cell death creates the segmental boundary between the maxilla and mandible of the head	DEFORMED (activates reaper)
	dapentaplegic	prevents the above cell changes in more posterior positions	ABDOMINAL-B (repress decapentaplegic)
Mouse	EphA7	Cell adhesion: causes tight association of cells in distal limb that will form digit, carpal and tarsal bones	HOX-A13 (activates EphA7)
	Cdkn1a	Cell cycle: differentiation of myelomonocyte cells into monocytes (white blood cells), with cell cycle arrest	Hox-A10 (activates Cdkn1a)

Enhancer sequences that are bound by homeodomains

The DNA sequence that is bound by the homeodomain protein contains the nucleotide sequence TAAT, with the 5'

Directionality (molecular biology)

Directionality, in molecular biology and biochemistry, is the end-to-end chemical orientation of a single strand of nucleic acid. The chemical convention of naming carbon atoms in the nucleotide sugar-ring numerically gives rise to a 5′-end and a 3′-end...

 terminal T being the most important for binding. This sequence is conserved in nearly all sites recognized by homeodomains, and probably distinguishes such locations as DNA binding sites. The base pairs following this initial sequence are used to distinguish between homeodomain proteins, all of which have similar recognition sites. For instance, the nucleotide following the TAAT sequence is recognized by the amino acid at position 9 of the homeodomain protein. In the maternal protein Bicoid, this position is occupied by lysine

Lysine

Lysine is an α-amino acid with the chemical formula HO2CCH4NH2. It is an essential amino acid, which means that the human body cannot synthesize it. Its codons are AAA and AAG....

, which recognizes and binds to the nucleotide guanine

Guanine

Guanine is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine . In DNA, guanine is paired with cytosine. With the formula C5H5N5O, guanine is a derivative of purine, consisting of a fused pyrimidine-imidazole ring system with...

. In Antennapedia

Antennapedia

Antennapedia is a HOM-C gene first discovered in Drosophila which controls the formation of legs during development. Loss-of-function mutations in the regulatory region of this gene result in the development of the second leg pair into ectopic antennae...

, this position is occupied by glutamine

Glutamine

Glutamine is one of the 20 amino acids encoded by the standard genetic code. It is not recognized as an essential amino acid but may become conditionally essential in certain situations, including intensive athletic training or certain gastrointestinal disorders...

, which recognizes and binds to adenine

Adenine

Adenine is a nucleobase with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate and the cofactors nicotinamide adenine dinucleotide and flavin adenine dinucleotide , and protein synthesis, as a chemical component of DNA...

. If the lysine in Bicoid is replaced by glutamine, the resulting protein will recognize Antennapedia-binding enhancer sites.

Regulation of Hox genes

Just as Hox genes regulate realisator genes, they are in turn regulated themselves by gap gene

Gap gene

A gap gene is a type of gene involved in the development of the segmented embryos of some arthropods. Gap genes are defined by the effect of a mutation in that gene, which causes the loss of contiguous body segments, resembling a gap in the normal body plan...

s and pair-rule genes, which are in their turn regulated by maternally-supplied mRNA

Messenger RNA

Messenger RNA is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcribed from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes. Here, the nucleic acid polymer is translated into a polymer of amino acids: a protein...

. This results in a transcription factor cascade: maternal factors activate gap or pair-rule genes; gap and pair-rule genes activate Hox genes; then, finally, Hox genes activate realisator genes that cause the segments in the developing embryo to differentiate.
Regulation is achieved via protein concentration gradients, called morphogenic fields

Morphogenetic field

In developmental biology, a morphogenetic field is a group of cells able to respond to discrete, localized biochemical signals leading to the development of specific morphological structures or organs. The spatial and temporal extent of the embryonic fields are dynamic, and within the field is a...

. For example, high concentrations of one maternal protein and low concentrations of others will turn on a specific set of gap or pair-rule genes. In flies, stripe 2 in the embryo is activated by the maternal proteins Bicoid and Hunchback, but repressed by the gap proteins Giant and Kruppel. Thus, stripe 2 will only form wherever there is Bicoid and Hunchback, but not where there is Giant and Kruppel.

MicroRNA strands located in hox clusters have been shown to inhibit more anterior hox genes ("posterior prevalence phenomenon"), possibly to better fine tune its expression pattern.

Non-coding RNA

Non-coding RNA

A non-coding RNA is a functional RNA molecule that is not translated into a protein. Less-frequently used synonyms are non-protein-coding RNA , non-messenger RNA and functional RNA . The term small RNA is often used for short bacterial ncRNAs...

 (ncRNA) has been shown to be abundant in Hox clusters. In humans, 231 ncRNA may be present. One of these, HOTAIR

HOTAIR

HOTAIR is a gene at size 6,232 bp encoding 2.2 kbp long noncoding RNA molecule, which controls gene expression on chromosome 2. Its source DNA is located within a HOXC gene cluster. It is the first example of an RNA expressed on one chromosome influencing transcription on another chromosome...

, silences in trans (it is transcribed from the HOXC cluster and inhibits late HOXD genes) by binding to Polycomb-group proteins

Polycomb-group proteins

Polycomb-group proteins are a family of proteins first discovered in fruit flies that can remodel chromatin such that epigenetic silencing of genes takes place...

 (PRC2).

The chromatin

Chromatin

Chromatin is the combination of DNA and proteins that make up the contents of the nucleus of a cell. The primary functions of chromatin are; to package DNA into a smaller volume to fit in the cell, to strengthen the DNA to allow mitosis and meiosis and prevent DNA damage, and to control gene...

 structure is essential for transcription but it also requires the cluster to loop out of the chromosomal territory.

In higher animals and humans, retinoic acid

Retinoic acid

Retinoic acid is a metabolite of vitamin A that mediates the functions of vitamin A required for growth and development. Retinoic acid is required in chordate animals which includes all higher animals from fishes to humans...

 regulates differential expression of Hox genes along the anteroposterior axis. 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.

Quantitative PCR has shown several trends regarding colinearity: the system is in equlibrium and the total number of transcripts depends on the number of genes present according to a linear relationship.

Homeotic mutations

Incorrect expression of Hox genes can lead to major changes in the morphology of the individual. Homeotic mutations were first identified in 1894, when William Bateson

William Bateson

William Bateson was an English geneticist and a Fellow of St. John's College, Cambridge...

 noticed that floral stamen

Stamen

The stamen is the pollen producing reproductive organ of a flower...

s occasionally appeared in the wrong place; he found four example flowers in which the stamens would grow in the place where petals normally grow.

In the late 1940s, Edward Lewis began studying homeotic mutation on Drosophila melanogaster

Drosophila melanogaster

Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...

 which caused bizarre rearrangements of body parts. Mutations in the genes that code for limb development can cause deformity or lead to death. For an example, mutations in the Antennapedia gene cause legs instead of the antenna to develop on the head of a fly.

Another famous example in the Drosophila melanogaster

Drosophila melanogaster

Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...

is the mutation of the Ultrabithorax

Ultrabithorax

Ultrabithorax or Ubx is a member of the homeobox gene family. Homeobox proteins function as transcription factors. In Drosophila melanogaster it is expressed in the third thoracic and first abdominal segments and represses wing formation. The Ubx gene regulates the decisions regarding the...

 Hox gene, which specifies the 3rd thoracic segment. Normally, this segment displays a pair of legs and a pair of halteres (a reduced pair of wings used for balancing). In the mutant lacking functional Ultrabithorax protein, the 3rd thoracic segment now expresses the same structures found on the segment to its immediate anterior, the 2nd thoracic segment, which contains a pair of legs and a pair of (fully developed) wings. These mutants sometimes occur in wild populations of flies, and it was these mutants that led to the discovery of Hox genes.

Colinearity of Hox genes

In some organisms, especially vertebrates, the various Hox genes are situated very close to one another on the chromosome in groups or clusters.
Interestingly, the order of the genes on the chromosome is the same as the expression of the genes in the developing embryo, with the first gene being expressed in the anterior end of the developing organism. The reason for this colinearity is not yet completely understood. The diagram above shows the relationship between the genes and protein expression in flies.

Hox nomenclature

Hox genes in different phyla have been given different names, which has led to confusion about nomenclature. The complement of Hox genes of the Ecdysozoa

Ecdysozoa

Ecdysozoa is a group of protostome animals, including Arthropoda , Nematoda, and several smaller phyla. They were first defined by Aguinaldo et al. in 1997, based mainly on trees constructed using 18S ribosomal RNA genes...

 (arthropods, nematodes, and so on) is made up of two clusters, the Antennapedia

Antennapedia

Antennapedia is a HOM-C gene first discovered in Drosophila which controls the formation of legs during development. Loss-of-function mutations in the regulatory region of this gene result in the development of the second leg pair into ectopic antennae...

 complex and the Bithorax complex, which together are referred to as the HOM-C (for Homeotic Complex). Hox genes in deuterostomes (echinoderms, chordates) are correctly referred to as Hox genes, and are arranged in four clusters: Hoxa, Hoxb, Hoxc, and Hoxd. Although it is technically incorrect to refer to homeotic genes in non-deuterostome phyla as "Hox genes", the practice of using "Hox" in place of "Hom-C" is now acceptable even in the scientific literature.

Human genes

Humans contain Hox genes in four clusters:

cluster	chromosome Chromosome A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...	genes
HOXA	chromosome 7	HOXA1 HOXA1 Homeobox protein Hox-A1 is a protein that in humans is encoded by the HOXA1 gene.- Gene :Two transcript variants encoding two different isoforms have been found for this gene, with only one of the isoforms containing the homeodomain region.... , HOXA2 HOXA2 Homeobox protein Hox-A2 is a protein that in humans is encoded by the HOXA2 gene.- Function :In vertebrates, the genes encoding the class of transcription factors called homeobox genes are found in clusters named A, B, C, and D on four separate chromosomes. Expression of these proteins is spatially... , HOXA3 HOXA3 Homeobox protein Hox-A3 is a protein that in humans is encoded by the HOXA3 gene.- Regulation :The HOXA3 gene is repressed by the microRNA miR-10a.... , HOXA4 HOXA4 Homeobox A4, also known as HOXA4, is a protein which in humans is encoded by the HOXA4 gene.- Function :In vertebrates, the genes encoding the class of transcription factors called homeobox genes are found in clusters named A, B, C, and D on four separate chromosomes. Expression of these proteins... , HOXA5 HOXA5 Homeobox protein Hox-A5 is a protein that in humans is encoded by the HOXA5 gene.-Further reading:- External links :... , HOXA6 HOXA6 Homeobox protein Hox-A6 is a protein that in humans is encoded by the HOXA6 gene.-Further reading:... , HOXA7 HOXA7 Homeobox protein Hox-A7 is a protein that in humans is encoded by the HOXA7 gene.-Further reading:... , HOXA9 HOXA9 Homeobox protein Hox-A9 is a protein that in humans is encoded by the HOXA9 gene.-Interactions:HOXA9 has been shown to interact with PBX2, TRIP6 and MEIS1.-Further reading:... , HOXA10, HOXA11 HOXA11 Homeobox protein Hox-A11 is a protein that in humans is encoded by the HOXA11 gene.... , HOXA13 HOXA13 Homeobox protein Hox-A13 is a protein that in humans is encoded by the HOXA13 gene.- Function :In vertebrates, the genes encoding the class of transcription factors called homeobox genes are found in clusters named A, B, C, and D on four separate chromosomes. Expression of these proteins is...
HOXB	chromosome 17	HOXB1 HOXB1 Homeobox protein Hox-B1 is a protein that in humans is encoded by the HOXB1 gene.-Further reading:... , HOXB2 HOXB2 Homeobox protein Hox-B2 is a protein that in humans is encoded by the HOXB2 gene.... , HOXB3 HOXB3 Homeobox protein Hox-B3 is a protein that in humans is encoded by the HOXB3 gene.... , HOXB4 HOXB4 Homeobox protein Hox-B4 is a protein that in humans is encoded by the HOXB4 gene.... , HOXB5 HOXB5 Homeobox protein Hox-B5 is a protein that in humans is encoded by the HOXB5 gene.-Further reading:... , HOXB6 HOXB6 Homeobox protein Hox-B6 is a protein that in humans is encoded by the HOXB6 gene.-Further reading:... , HOXB7 HOXB7 Homeobox protein Hox-B7 is a protein that in humans is encoded by the HOXB7 gene.-Interactions:HOXB7 has been shown to interact with PBX1 and CREB-binding protein.-Further reading:... , HOXB8 HOXB8 Homeobox protein Hox-B8 is a protein that in humans is encoded by the HOXB8 gene.Transplantation of normal bone marrow into a Hoxb8 mutant mouse results is a reduction of compulsive grooming.... , HOXB9 HOXB9 Homeobox protein Hox-B9 is a protein that in humans is encoded by the HOXB9 gene.-Interactions:HOXB9 has been shown to interact with BTG2 and BTG1.... , HOXB13 HOXB13 Homeobox protein Hox-B13 is a protein that in humans is encoded by the HOXB13 gene.-Further reading:...
HOXC	chromosome 12	HOXC4 HOXC4 Homeobox protein Hox-C4 is a protein that in humans is encoded by the HOXC4 gene.... , HOXC5 HOXC5 Homeobox protein Hox-C5 is a protein that in humans is encoded by the HOXC5 gene.... , HOXC6 HOXC6 Homeobox protein Hox-C6 is a protein that in humans is encoded by the HOXC6 gene.-Further reading:... , HOXC8 HOXC8 Homeobox protein Hox-C8 is a protein that in humans is encoded by the HOXC8 gene.-Interactions:HOXC8 has been shown to interact with Mothers against decapentaplegic homolog 6 and Mothers against decapentaplegic homolog 1.... , HOXC9 HOXC9 Homeobox protein Hox-C9 is a protein that in humans is encoded by the HOXC9 gene.... , HOXC10 HOXC10 Homeobox protein Hox-C10 is a protein that in humans is encoded by the HOXC10 gene.... , HOXC11 HOXC11 Homeobox protein Hox-C11 is a protein that in humans is encoded by the HOXC11 gene.... , HOXC12 HOXC12 Homeobox C12 is a protein that in humans is encoded by the HOXC12 gene.This gene belongs to the homeobox family of genes. The homeobox genes encode a highly conserved family of transcription factors that play an important role in morphogenesis in all multicellular organisms... , HOXC13 HOXC13 Homeobox protein Hox-C13 is a protein that in humans is encoded by the HOXC13 gene....
HOXD	chromosome 2	HOXD1 HOXD1 Homeobox protein Hox-D1 is a protein that in humans is encoded by the HOXD1 gene.- External links :... , HOXD3 HOXD3 Homeobox protein Hox-D3 is a protein that in humans is encoded by the HOXD3 gene.- External links :... , HOXD4 HOXD4 Homeobox protein Hox-D4 is a protein that in humans is encoded by the HOXD4 gene.- External links :... , HOXD8 HOXD8 Homeobox protein Hox-D8 is a protein that in humans is encoded by the HOXD8 gene.- External links :... , HOXD9 HOXD9 Homeobox protein Hox-D9 is a protein that in humans is encoded by the HOXD9 gene.-Further reading:- External links :... , HOXD10 HOXD10 Homeobox D10, also known as HOXD10, is a protein which in humans is encoded by the HOXD10 gene.- Function :This gene is a member of the Abd-B homeobox family and encodes a protein with a homeobox DNA-binding domain. It is included in a cluster of homeobox D genes located on chromosome 2... , HOXD11 HOXD11 Homeobox protein Hox-D11 is a protein that in humans is encoded by the HOXD11 gene.This gene belongs to the homeobox family of genes. The homeobox genes encode a highly conserved family of transcription factors that play an important role in morphogenesis in all multicellular organisms... , HOXD12 HOXD12 Homeobox protein Hox-D12 is a protein that in humans is encoded by the HOXD12 gene.This gene belongs to the homeobox family of genes. The homeobox genes encode a highly conserved family of transcription factors that play an important role in morphogenesis in all multicellular organisms... , HOXD13 HOXD13 Homeobox protein Hox-D13 is a protein that in humans is encoded by the HOXD13 gene.This gene belongs to the homeobox family of genes. The homeobox genes encode a highly conserved family of transcription factors that play an important role in morphogenesis in all multicellular organisms...

History

Christiane Nüsslein-Volhard

Christiane Nüsslein-Volhard

Christiane Nüsslein-Volhard is a German biologist who won the Albert Lasker Award for Basic Medical Research in 1991 and the Nobel Prize in Physiology or Medicine in 1995, together with Eric Wieschaus and Edward B...

 and Eric F. Wieschaus

Eric F. Wieschaus

-External links:***, excellent profile**...

 identified and classified 15 genes of key importance in determining the body plan and the formation of body segments of the fruit fly Drosophila melanogaster.
Edward B. Lewis

Edward B. Lewis

- External links :* *...

 studied the next step - Hox genes that govern the development of a larval segment into a specific body segment. Homeotic means that something has been changed into the likeness of something else. Lewis found a colinearity in time and space between the order of the genes in the bithorax complex and their affected regions in the segments. For their work they were awarded the Nobel Prize in Physiology or Medicine

Nobel Prize in Physiology or Medicine

The Nobel Prize in Physiology or Medicine administered by the Nobel Foundation, is awarded once a year for outstanding discoveries in the field of life science and medicine. It is one of five Nobel Prizes established in 1895 by Swedish chemist Alfred Nobel, the inventor of dynamite, in his will...

in 1995.

External links

• The Homeotic Selector Genes in Developmental Biology, 6th Edition by Scott F. Gilbert (2000) Published by Sinauer Associates, Inc. ISBN 0-87893-243-7.