Juno also known as folate receptor 4, folate receptor delta or IZUMO1R is a
protein that in humans is encoded by the ''FOLR4''
gene.
Juno is a member of the
folate receptor family
and is
GPI-anchored to the
plasmalemma of the mammalian
egg cell
The egg cell, or ovum (plural ova), is the female reproductive cell, or gamete, in most anisogamous organisms (organisms that reproduce sexually with a larger, female gamete and a smaller, male one). The term is used when the female gamete is ...
that recognizes its
sperm
Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...
-riding counterpart,
IZUMO1, and facilitates
fertilization. The protein was named after
Juno, 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, 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
Infertility is the inability of a person, animal or plant to reproduce by natural means. It is usually not the natural state of a healthy adult, except notably among certain eusocial species (mostly haplodiploid insects). It is the normal state ...
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.
Juno was initially found in murine
oocytes, 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, in collaboration with the group at the
Wellcome Trust Sanger Institute.
[ ]
Model organisms
Model organism
A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workin ...
s have been used in the study of JUNO function. A conditional
knockout mouse line called ''Izumo1r
tm2a(KOMP)Wtsi'' was generated at the
Wellcome Trust Sanger Institute.
Male and female animals underwent a standardized
phenotypic screen to determine the effects of deletion.
Additional screens performed: - In-depth immunological phenotyping
References
{{reflist, 33em
Animal proteins
Fertility
Mammal female reproductive system