Juno also known as folate receptor 4, folate receptor delta or IZUMO1R is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

that in humans is encoded by the ''FOLR4''

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 ...

. Juno is a member of the folate receptor family and is GPI-anchored to the

plasmalemma The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (th ...

of the mammalian egg cell that recognizes its sperm-riding counterpart, IZUMO1, and facilitates

fertilization Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...

. The protein was named after

Juno Juno commonly refers to: *Juno (mythology), the Roman goddess of marriage and queen of the gods *Juno (film), ''Juno'' (film), 2007 Juno may also refer to: Arts, entertainment and media Fictional characters *Juno, in the film ''Jenny, Juno'' *Ju ...

, the Roman goddess of fertility and marriage. 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 Intracytoplasmic sperm injection (ICSI ) is an in vitro fertilization (IVF) procedure in which a single sperm cell is injected directly into the cytoplasm of an egg. This technique is used in order to prepare the gametes for the obtention of em ...

, the egg cell does not lose cell-surface expression of Juno, which suggests that Juno contributes to the prevention of

polyspermy In biology, polyspermy describes the fertilization of an egg by more than one sperm. Diploid organisms normally contain two copies of each chromosome, one from each parent. The cell resulting from polyspermy, on the other hand, contains three or ...

. 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 A university () is an institution of higher (or tertiary) education and research which awards academic degrees in several academic disciplines. Universities typically offer both undergraduate and postgraduate programs. In the United States, ...

. In 2014, the function of folate receptor 4 was discovered by the researchers of the

Wellcome Trust Sanger Institute The Wellcome Sanger Institute, previously known as The Sanger Centre and Wellcome Trust Sanger Institute, is a non-profit British genomics and genetics research institute, primarily funded by the Wellcome Trust. It is located on the Wellcome G ...

who also proposed that the protein be renamed as Juno. Juno was initially found in murine

oocytes An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female g ...

, but its interaction with Izumo was subsequently found in other mammalian species, including humans. Being previously elusive, Juno was discovered nine years after its male counterpart, Izumo1.

3D structure

The crystal structure of Juno () was reported in February 2016 by researchers at

Karolinska Institutet The Karolinska Institute (KI; sv, Karolinska Institutet; sometimes known as the (Royal) Caroline Institute in English) is a research-led medical university in Solna within the Stockholm urban area of Sweden. The Karolinska Institute is consist ...

, in collaboration with the group at the

Model organisms

Model organisms have been used in the study of JUNO function. A conditional

knockout mouse A knockout mouse, or knock-out mouse, is a genetically modified mouse (''Mus musculus'') in which researchers have inactivated, or " knocked out", an existing gene by replacing it or disrupting it with an artificial piece of DNA. They are importa ...

line called ''Izumo1r^{tm2a(KOMP)Wtsi}'' was generated at the

. Male and female animals underwent a standardized

phenotypic screen In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...

to determine the effects of deletion. Additional screens performed: - In-depth immunological phenotyping

References

{{reflist, 33em Animal proteins Fertility Mammal female reproductive system