Retinal homeobox protein Rx also known asretina and anterior neural fold homeobox is aprotein that in humans is encoded by the RAXgene.[5] The RAX gene is located on chromosome 18 in humans, mice, and rats.[6]
This gene encodes ahomeobox-containingtranscription factor that functions in eye development. The gene is expressed early in the eyeprimordia, and is required for retinal cell fate determination and also regulates stem cell proliferation.[5]
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.[7]
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,[8] the Rax gene is known to contribute to the development of the retina,hypothalamus,pineal gland andpituitary gland.[9]
Mutations to the Rax gene cause malformation of the retinal field, including anophthalmia and microphthalmia.[10]
Individuals who have a mutation in the RAX gene fail to develop ocular structures, referred to as anophthalmia.[7] RAX mutant individuals can also have microphthalmia, where one or both of the eyes is smaller than normal.[6]
Rax genes are conserved among vertebrates. RAX knockout mice have no eyes and abnormal forebrain formation. In the frogXenopus tropicalis, Rax mutants are eyeless; the future retinal tissue instead has diencephalon and telencephalon features.[11] Due to a genome duplication at the basis of the teleost fish lineage, fishes contain three Rax genes: Rx1, Rx2, and Rx3.[12]Zebrafish andmedaka mutants in Rx3 are eyeless.[12][13]
