“Bouncer”, the gate-keeper of the egg, controls sperm entry

Fertilization is fundamental for sexual reproduction, yet its molecular mechanisms are poorly understood. IMP scientists now found a protein that controls sperm entry into an egg.

Andrea Pauli’s lab at the IMP found that an oocyte-expressed Ly6/uPAR protein, which the researchers named “Bouncer” due to its gate-keeping function, is a crucial fertilization factor in zebrafish. Membrane-bound Bouncer mediates sperm-egg binding and is thus essential for sperm entry into the egg.

Remarkably, Bouncer is not only required for sperm-egg interaction, but is also sufficient to allow cross-species fertilization between zebrafish and medaka, two fish species that diverged more than 200 million years ago. The study, recently published in “Science”, thus identifies Bouncer as a key determinant of species-specific fertilization in fish.

“Our study is the first report of a protein in any organism allowing entry of another species’ sperm”, says Sarah Herberg, a Vienna BioCenter PhD student and a co-author of the publication. Bouncer’s closest homolog in tetrapods, SPACA4, is restricted to the male germline in internally fertilizing vertebrates, which suggests that the findings in fish are relevant to human biology.


Original Publication:
Sarah Herberg, Krista R. Gert, Alexander Schleiffer and Andrea Pauli: The Ly6/uPAR protein Bouncer is necessary and sufficient for species-specific fertilization.

Science, 7 September 2018.