Ultrabithorax (Ubx) is a homeobox

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

found in insects, and is used in the regulation of patterning 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 deve ...

. There are many possible products of this gene, which function as

transcription factors In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The fun ...

. Ubx is used in the specification of serially homologous structures, and is used at many levels of developmental hierarchies. In ''

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the " vinegar fly" or "pomace fly". Starting with ...

'' it is expressed in the third

thoracic The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...

(T3) and first

abdominal The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso ...

(A1) segments and represses

wing A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is e ...

formation. The Ubx gene regulates the decisions regarding the number of wings and legs the adult flies will have. The developmental role of the Ubx gene is determined by the splicing of its product, which takes place after translation of the gene. The specific splice factors of a particular cell allow the specific regulation of the developmental fate of that cell, by making different splice variants of transcription factors. In ''D. melanogaster'', at least six different

isoform A protein isoform, or "protein variant", is a member of a set of highly similar proteins that originate from a single gene or gene family and are the result of genetic differences. While many perform the same or similar biological roles, some iso ...

s of Ubx exist. Mutations of the Ubx gene will lead to transformation of dorsal and ventral appendages of the third thoracic segment (T3), which includes the

haltere ''Halteres'' (; singular ''halter'' or ''haltere'') (from grc, ἁλτῆρες, weights held in the hands to give an impetus in leaping) are a pair of small club-shaped organs on the body of two orders of flying insects that provide info ...

and third leg, into the counterparts on the second thoracic segment (T2). If Ubx is present in T3, it will prevent the original fate of the T2 segment. Such mutations can produce the second set of wings observed in the bithorax phenotype.

Structure

The Ubx gene contains a 5' exon, two micro-exons, an optional B element, and a C terminal exon. The Ubx genomic DNA length is 76 kb and its cDNA clone length is 3.2 to 4.6 kb. The 5' exon contains the 5' UTR which has 964 bases. The C terminal exon contains the 3'UTR which has 1580 to 2212 bases.

Target genes

Ubx targets hundreds of different genes at different stages of

including regulatory genes such as

, signalling components and terminal differentiation genes. Ubx has been shown to act upon long-range signaling molecules, as well as their target genes and subsequent genes further downstream. It has been shown to act at many levels of regulatory hierarchies, meaning Ubx can be used as a signal more than once in the same regulatory hierarchy. Ubx represses selected

Dpp DPP may stand for: Business *Digital Production Partnership, of UK public service broadcasters * Direct Participation Program, a financial security * Discounted payback period Photography * Digital Photo Professional, Canon software Law en ...

(

Decapentaplegic Decapentaplegic (Dpp) is a key morphogen involved in the development of the fruit fly ''Drosophila melanogaster'' and is the first validated secreted morphogen. It is known to be necessary for the correct patterning and development of the early ' ...

-activated) target genes in the anterior and posterior axis. Several Dpp target genes which have been identified are ''spalt-related, vestigial, Serum Response Factor,'' and ''achaete-scute.'' Ubx also represses

Wingless The Wnt signaling pathways are a group of signal transduction pathways which begin with proteins that pass signals into a cell through cell surface receptors. The name Wnt is a portmanteau created from the names Wingless and Int-1. Wnt signaling p ...

in the posterior compartment of the

dorsoventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

axis. The products of these genes are used in the regulation of morphological features between the wing and the

. Ubx also selectively represses one enhancer of the vestigial genes in the proximodistal axis. This gene is important for the development of hindwings in Lepidoptera, and leg development in larvae.

Regulation

Ubx is activated when there is a certain lack of

Hunchback Kyphosis is an abnormally excessive convex curvature of the spine as it occurs in the thoracic and sacral regions. Abnormal inward concave ''lordotic'' curving of the cervical and lumbar regions of the spine is called lordosis. It can result ...

(hb) protein. Significant concentrations of Hunchback only exist in the anterior and posterior regions of the embryo, therefore Ubx is expressed only in middle segments. Thus, the hb gene may play an important role in the specification of the boundaries of Ubx expression. Activation of Ubx involves multiple ''cis''-acting regulatory sequences, which are found upstream and downstream of the mRNA cap-site. These enhancer regions can activate transcription of Ubx if the right combination of factors is present. For example, it has been shown that Ubx expression in the third femur of ''D. melanogaster'' is dependent on the enhancer regions ''abx'' and ''pbx''. Transcription factors which bind to the promoter site of Ubx have been purified and shown to activate expression of the gene ''in vitro''. Expression of Ubx is repressed by the

long non-coding RNA Long non-coding RNAs (long ncRNAs, lncRNA) are a type of RNA, generally defined as transcripts more than 200 nucleotides that are not translated into protein. This arbitrary limit distinguishes long ncRNAs from small non-coding RNAs, such as mi ...

Bithoraxoid (Bxd), using transcriptional interference to silence expression.

Ubx Biomaterials

Besides being a well known transcription factor, Ubx has been used to form biomaterials ''in vitro''. Macroscale materials in the form of ropes, films and sheets can be generated from recombinant Ubx protein, which can self-assemble under gentler conditions than other biomaterial proteins. The macroscale materials self-adhere, allowing them to assume more complex structures. In addition to requiring less harsh conditions than other proteins, Ubx has been shown to assemble more rapidly and at much lower concentrations. Ubx materials are mechanically robust. By altering fiber diameter, the breaking strength, breaking strain, and Young’s modulus can be tuned to values spanning an order of magnitude, ultimately changing the mechanism of extension.

References

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External links

''Drosophila'' ''Ultrabithorax'' - The Interactive FlyGoogle search for images
Drosophila melanogaster genes Transcription factors Homeobox genes