Biology:Retinal homeobox protein Rx

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Short description: Protein-coding gene in the species Homo sapiens


A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example

Retinal homeobox protein Rx also known as retina and anterior neural fold homeobox is a protein that in humans is encoded by the RAX gene.[1] The RAX gene is located on chromosome 18 in humans, mice, and rats.[2]

Function

This gene encodes a homeobox-containing transcription factor that functions in eye development. The gene is expressed early in the eye primordia, and is required for retinal cell fate determination and also regulates stem cell proliferation.[1]

Towards the end of late gastrulation a single eye field has formed and splits into bilateral fields via action by the signaling molecule, sonic hedgehog (Shh) secreted from the forebrain. Rax and Six-3 (also a transcription factor) maintain the forebrain's ability to secrete Shh by inhibiting activity of the signaling molecule Wnt.[3]

Rax (Retina and Anterior Neural Fold Homeobox) is a gene in the OAR (Otx, Arx,& Rax) subgroup of the paired-like homeodomain family of transcription factors. Discovered in 1997,[4] the Rax gene is known to contribute to the development of the retina, hypothalamus, pineal gland and pituitary gland.[5]

Clinical significance

Mutations in this gene have been reported in patients with defects in ocular development, including microphthalmia, anophthalmia, and coloboma.[1]

Mutations to the Rax gene cause malformation of the retinal field, including anophthalmia and microphthalmia.[6]

Individuals who have a mutation in the RAX gene fail to develop ocular structures, referred to as anophthalmia.[3] RAX mutant individuals can also have microphthalmia, where one or both of the eyes is smaller than normal.[2]

Animal studies

Rax genes are conserved among vertebrates. RAX knockout mice have no eyes and abnormal forebrain formation. In the frog Xenopus tropicalis, Rax mutants are eyeless; the future retinal tissue instead has diencephalon and telencephalon features.[7] Due to a genome duplication at the basis of the teleost fish lineage, fishes contain three Rax genes: Rx1, Rx2, and Rx3.[8] Zebrafish and medaka mutants in Rx3 are eyeless.[8][9]

References

  1. ↑ 1.0 1.1 1.2 "Entrez Gene: Retina and anterior neural fold homeobox". https://www.ncbi.nlm.nih.gov/gene/30062. 
  2. ↑ 2.0 2.1 "An essential role for Rax in retina and neuroendocrine system development". Development, Growth & Differentiation 54 (3): 341–8. Apr 2012. doi:10.1111/j.1440-169X.2012.01337.x. PMID 22524605. 
  3. ↑ 3.0 3.1 Carlson, Bruce M. (2014). "Sense Organs". Human Embryology and Developmental Biology (5th ed.). Elsevier/Saunders. pp. 270–71. ISBN 978-1-4557-2794-0. 
  4. ↑ "rax, a novel paired-type homeobox gene, shows expression in the anterior neural fold and developing retina". Proceedings of the National Academy of Sciences of the United States of America 94 (7): 3088–93. Apr 1997. doi:10.1073/pnas.94.7.3088. PMID 9096350. Bibcode: 1997PNAS...94.3088F. 
  5. ↑ "The Rx homeobox gene is essential for vertebrate eye development". Nature 387 (6633): 603–7. Jun 1997. doi:10.1038/42475. PMID 9177348. Bibcode: 1997Natur.387..603M. 
  6. ↑ "Mutations in the human RAX homeobox gene in a patient with anophthalmia and sclerocornea". Human Molecular Genetics 13 (3): 315–22. Feb 2004. doi:10.1093/hmg/ddh025. PMID 14662654. 
  7. ↑ "Xenopus mutant reveals necessity of rax for specifying the eye field which otherwise forms tissue with telencephalic and diencephalic character". Developmental Biology 395 (2): 317–330. Nov 2014. doi:10.1016/j.ydbio.2014.09.004. PMID 25224223. 
  8. ↑ 8.0 8.1 Furutani-Seiki, Makoto; Wittbrodt, Joachim (2004-07-01). "Medaka and zebrafish, an evolutionary twin study". Mechanisms of Development 121 (7): 629–637. doi:10.1016/j.mod.2004.05.010. ISSN 0925-4773. PMID 15210172. 
  9. ↑ Loosli, Felix; Staub, Wendy; Finger-Baier, Karin C; Ober, Elke A; Verkade, Heather; Wittbrodt, Joachim; Baier, Herwig (2003-09-01). "Loss of eyes in zebrafish caused by mutation of chokh/rx3". EMBO Reports 4 (9): 894–899. doi:10.1038/sj.embor.embor919. ISSN 1469-221X. PMID 12947416. 

This article incorporates text from the United States National Library of Medicine, which is in the public domain.





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