Juno (protein)
{{Short description|Protein-coding gene in the species Homo sapiens}}
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Juno also known as folate receptor 4, folate receptor delta or IZUMO1R is a protein that in humans is encoded by the FOLR4 gene.{{cite web | title = Entrez Gene: Folate receptor 4, delta (putative) | url = https://www.ncbi.nlm.nih.gov/gene/390243 }} Juno is a member of the folate receptor family{{cite journal | vauthors = Spiegelstein O, Eudy JD, Finnell RH | title = Identification of two putative novel folate receptor genes in humans and mouse | journal = Gene | volume = 258 | issue = 1–2 | pages = 117–25 | date = Nov 2000 | pmid = 11111049 | doi = 10.1016/S0378-1119(00)00418-2 }} and is GPI-anchored to the plasmalemma of the mammalian egg cell that recognizes its sperm-riding counterpart, IZUMO1, and facilitates fertilization. The protein was named after Juno, the Roman goddess of fertility and marriage.{{cite web | url = http://www.sanger.ac.uk/about/press/2014/140416.html | title = Sperm meets egg: protein essential for fertilization discovered | publisher = Wellcome Trust Sanger Institute | date=16 April 2014 | access-date =16 April 2014}}
After the initial fertilisation stage, a sudden decrease of Juno from the egg cell surface occurs and Juno becomes virtually undetectable after just 40 minutes. Still, after fertilization via intracytoplasmic sperm injection, the egg cell does not lose cell-surface expression of Juno, which suggests that Juno contributes to the prevention of polyspermy. Mice lacking Juno on the surface of their egg cells are infertile because their egg cells do not fuse with normal sperm, demonstrating Juno's essential role in the fertility of female mice.
Discovery
Based on a sequence homology search for genes relate to the folate receptor, the gene for folate receptor 4 was first identified in mice and humans in 2000 at the University of Nebraska.
In 2014, the function of folate receptor 4 was discovered by the researchers of the Wellcome Trust Sanger Institute who also proposed that the protein be renamed as Juno.{{cite web | url =http://www.genengnews.com/gen-news-highlights/sperm-egg-fusion-depends-on-pairing-of-his-her-proteins/81249756/| title = Sperm/Egg Fusion Depends on Pairing of His/Her Proteins | publisher = Genetic Engineering & Biotechnology News | author = Mayer K | date = 16 April 2014| access-date = 16 April 2014}} Juno was initially found in murine oocytes, but its interaction with Izumo was subsequently found in other mammalian species, including humans.{{cite journal | vauthors = Bianchi E, Doe B, Goulding D, Wright GJ | title = Juno is the egg Izumo receptor and is essential for mammalian fertilization | journal = Nature | volume = 508 | issue = 7497 | pages = 483–7 | date = Apr 2014 | pmid = 24739963 | doi = 10.1038/nature13203 | pmc=3998876| bibcode = 2014Natur.508..483B }}{{cite journal | url = http://cen.acs.org/articles/92/i16/Sperm-Protein-Meets-Match.html | title = Sperm Protein Meets Its Match | journal = Chemical & Engineering News | author = Everts S | volume = 92 | issue = 16 | date = 16 April 2014 }}{{cite web | url = http://www.medicaldaily.com/juno-protein-connects-egg-sperm-scientists-finally-unravel-mystery-how-cells-bond-276940| title ='Juno' Protein Connects Egg To Sperm; Scientists Finally Unravel Mystery Of How The Cells Bond | publisher = Medical Daily | author = Anthony Rivas | date=16 April 2014 | access-date =16 April 2014 }} Being previously elusive, Juno was discovered nine years after its male counterpart, Izumo1.
3D structure
The crystal structure of Juno ({{PDB|5EJN}}) was reported in February 2016 by researchers at Karolinska Institutet, in collaboration with the group at the Wellcome Trust Sanger Institute.{{cite journal |vauthors=Han L, Nishimura K, Sadat Al Hosseini H, Bianchi E, Wright GJ, Jovine L | title = Divergent evolution of vitamin B9 binding underlies Juno-mediated adhesion of mammalian gametes |journal=Curr. Biol. |volume=26 |issue= 3 |pages= R100-1 |year= 2016 |pmid= 26859261 |doi= 10.1016/j.cub.2015.12.034 | pmc=4751342| bibcode = 2016CBio...26.R100H }} {{PDB|5EJN}}