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Homeotic gene

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Homeotic genesare genes which regulate the development of anatomical structures in various organisms such as echinoderms,[1]insects, mammals, and plants. Homeotic genes often encodetranscription factorproteins, and these proteins affect development by regulating downstream gene networks involved in body patterning.[2]

Mutationsin homeotic genes cause displaced body parts (homeosis), such as antennae growing at the posterior of the fly instead of at the head.[3]Mutations that lead to development of ectopic structures are usually lethal.[4]

Types[edit]

There are several subsets of homeotic genes. They include many of theHoxandParaHoxgenes that are important forsegmentation.[5]Hox genes are found in bilateral animals, includingDrosophila(in which they were first discovered) and humans. Hox genes are a subset of thehomeoboxgenes. The Hox genes are oftenconservedacross species, so some of the Hox genes ofDrosophilaare homologous to those in humans. In general, Hox genes play a role of regulating expression of genes as well as aiding in development and assignment of specific structures during embryonic growth. This can range from segmentation inDrosophilatocentral nervous system(CNS) development in vertebrates.[6]Both Hox and ParaHox are grouped as HOX-Like (HOXL) genes, a subset of the ANTP class (named after theDrosophilagene,Antennapedia).[7]

They also include theMADS-box-containing genes involved in theABC model of flower development.[8]Besides flower-producing plants, the MADS-box motif is also present in other organisms such as insects, yeasts, and mammals. They have various functions depending on the organism including flower development, proto-oncogene transcription, and gene regulation in specific cells (such as muscle cells).[9]

Despite the terms being commonly interchanged, not all homeotic genes are Hox genes; the MADS-box genes are homeotic but not Hox genes. Thus, the Hox genes are a subset of homeotic genes.

Drosophila melanogaster[edit]

Homeotic selector gene complexes in the fruit flyDrosophila melanogaster

One of the most commonly studiedmodel organismsin regards to homeotic genes is the fruit flyDrosophila melanogaster.Its homeotic Hox genes occur in either the Antennapedia complex (ANT-C) or the Bithorax complex (BX-C) discovered byEdward B. Lewis.[10]Each of the complexes focuses on a different area of development. Theantennapediacomplex consists of five genes, includingproboscipedia,and is involved in the development of the front of the embryo, forming the segments of the head and thorax.[11]The bithorax complex consists of three main genes and is involved in the development of the back of the embryo, namely the abdomen and the posterior segments of the thorax.[12]

During development (starting at theblastodermstage of the embryo), these genes are constantly expressed to assign structures and roles to the different segments of the fly's body.[13]ForDrosophila,these genes can be analyzed using theFlybasedatabase.

Research[edit]

Much research has been done on homeotic genes in different organisms, ranging from basic understanding of how the molecules work to mutations to how homeotic genes affect the human body. Changing the expression levels of homeotic genes can negatively impact the organism. For example, in one study, a pathogenic phytoplasma caused homeotic genes in a flowering plant to either be significantly upregulated or downregulated. This led to severe phenotypic changes including dwarfing, defects in the pistils, hypopigmentation, and the development of leaf-like structures on most floral organs.[14]In another study, it was found that the homeotic geneCdx2acts as atumor suppressor.In normal expression levels, the gene prevents tumorgenesis and colorectal cancer when exposed tocarcinogens;however, whenCdx2was not well expressed, carcinogens caused tumor development.[15]These studies, along with many others, show the importance of homeotic genes even after development.

See also[edit]

References[edit]

  1. ^Popodi E, et al. (1996)."Sea Urchin Hox Genes: Insights into the Ancestral Hox Cluster".Mol. Biol. Evol.13(8): 1078–1086.doi:10.1093/oxfordjournals.molbev.a025670.PMID8865662.
  2. ^Hirth F, Hartmann B, Reichert H (May 1998). "Homeotic gene action in embryonic brain development ofDrosophila".Development.125(9): 1579–89.doi:10.1242/dev.125.9.1579.PMID9521896.
  3. ^Bürglin TR (2013). "Homeotic Mutation".Homeotic mutations.pp. 510–511.doi:10.1016/B978-0-12-374984-0.00727-0.ISBN978-0-08-096156-9.{{cite book}}:|journal=ignored (help)
  4. ^Andrew DJ, Horner MA, Petitt MG, et al. (March 1, 1994)."Setting limits on homeotic gene function: restraint ofSex combs reducedactivity byteashirtand other homeotic genes ".EMBO Journal.13(5): 1132–44.doi:10.1002/j.1460-2075.1994.tb06362.x.PMC394922.PMID7907545.
  5. ^Young T, Rowland JE, van de Ven C, et al. (October 2009)."Cdx and Hox genes differentially regulate posterior axial growth in mammalian embryos".Dev. Cell.17(4): 516–26.doi:10.1016/j.devcel.2009.08.010.PMID19853565.
  6. ^Akin ZN, Nazarali AJ (2005). "Hox Genes and Their Candidate Downstream Targets in the Developing Central Nervous System".Cellular and Molecular Neurobiology.25(3–4): 697–741.doi:10.1007/s10571-005-3971-9.PMID16075387.S2CID9804218.
  7. ^Holland PW, Booth HA, Bruford EA (2007)."Classification and nomenclature of all human homeobox genes".BMC Biology.5(1): 47.doi:10.1186/1741-7007-5-47.PMC2211742.PMID17963489.
  8. ^Theissen G (2001). "Development of floral organ identity: stories from the MADS house".Curr. Opin. Plant Biol.4(1): 75–85.Bibcode:2001COPB....4...75T.doi:10.1016/S1369-5266(00)00139-4.PMID11163172.
  9. ^Shore P, Sharrocks AD (1995). "The MADS-box family of transcription factors".European Journal of Biochemistry.229(1): 1–13.doi:10.1111/j.1432-1033.1995.0001l.x.PMID7744019.
  10. ^Heuer JG, Kaufman TC (May 1992). "Homeotic genes have specific functional roles in the establishment of theDrosophilaembryonic peripheral nervous system ".Development.115(1): 35–47.doi:10.1242/dev.115.1.35.PMID1353440.
  11. ^Randazzo FM, Cribbs DL, Kaufman TC (Sep 1991). "Rescue and regulation of proboscipedia: a homeotic gene of the Antennapedia Complex".Development.113(1): 257–71.doi:10.1242/dev.113.1.257.PMID1684932.
  12. ^Maeda RK, Karch F (Apr 2006). "The ABC of the BX-C: the bithorax complex explained".Development.133(8): 1413–22.doi:10.1242/dev.02323.PMID16556913.
  13. ^Breen TR, Harte PJ (January 1993). "trithoraxregulates multiple homeotic genes in the bithorax and Antennapedia complexes and exerts different tissue-specific, parasegment-specific and promoter-specific effects on each ".Development.117(1): 119–34.doi:10.1242/dev.117.1.119.PMID7900984.
  14. ^Himeno M, Neriya Y, et al. (July 1, 2011)."Unique morphological changes in plant pathogenic phytoplasma-infected petunia flowers are related to transcriptional regulation of floral homeotic genes in an organ-specific manner".The Plant Journal.67(6): 971–79.doi:10.1111/j.1365-313X.2011.04650.x.PMID21605209.
  15. ^Bonhomme C, Duluc I, et al. (October 2003)."TheCdx2homeobox gene has a tumour suppressor function in the distal colon in addition to a homeotic role during gut development ".Gut.52(10): 1465–71.doi:10.1136/gut.52.10.1465.PMC1773830.PMID12970140.

External links[edit]

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