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Requisite Protein Discovered that Enables Fertilization of an Egg by a Sperm

Every day more information and knowledge is discovered with respect to the basic science of fertility. The foundation of the study of fertility begins with how a sperm fertilizes an egg. Sperm undergo a variety of changes as they make their way from the ejaculate to the egg including hyperactivation, acrosome reaction and nuclear decondensation. Oocytes or eggs also undergo many changes almost immediately after fertilization. But the basics of the knowledge of fertilization itself remains, in large part, a work in progress. Recently, more progress in our understanding of fertilization has been made.

The Izumo-Juno pairing

Dr. Enrica Bianchi from the Welcome Trust Sanger Institute recently published in the Journal Nature regarding the discovery of a pairing of sperm-egg proteins which are essential to the process of fertilization. The Izumo-Juno pairing is the first known essential interaction for sperm-egg recognition in any mammal and is conserved among many mammals including mice as well as people.

Discovery

The Izumo protein on the sperm that recognizes the egg was identified in 2005 by Japanese researchers.
Dr. Bianchi’s group developed an artificial version of the Izumo protein in order to identify its counterpart on the surface of the egg.
The current discovery is the identification of folate receptor 4 on the egg which the authors propose to rename Juno (named after the Roman Goddess of fertility and marriage).

The Juno-egg protein becomes undetectable just 40 minutes after the initial pairing. There is speculation that this may be a safeguard in the prevention of polyspermy, or the fertilization of one egg by more than one sperm.

The team also developed mice that lacked the Juno protein and found that these mice were infertile and that their eggs did not fuse with normal sperm. Izumo deficient males are similarly infertile.

Development of new Diagnostic tests

Looking to the future, discoveries such as this may enable the development of new diagnostic tests for couples having difficulty to conceive. Conversely, more intimate knowledge of sperm egg interaction may also enable the development of new methods of contraception in the future.

Journal Reference:
Enrica Bianchi, Brendan Doe, David Goulding, Gavin J. Wright. Juno is the egg Izumo receptor and is essential for mammalian fertilization. Nature, 2014; DOI: 10.1038/nature13203

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