Matchmaking molecule for egg and sperm

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Science  07 Sep 2018:
Vol. 361, Issue 6406, pp. 974-975
DOI: 10.1126/science.aau8356

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The union of egg and sperm occurs at fertilization; this creates a zygote that will develop into a new, unique organism carrying a mixture of the parental genomes. Thus, sexual reproduction, involving two separate gametes, diversifies the genetic pool and accelerates evolution. However, the added necessity for fertilization poses challenges. First and foremost, specific matchmaking is critical. Sperm must meet egg, and exactly one sperm needs to fertilize exactly one egg because an unfertilized egg cannot develop, and fertilization with too many sperm (polyspermy) is equally fatal. Furthermore, fertilization has to provide a barrier between species by creating egg-sperm incompatibilities. Despite the fascinating biological questions, evolutionary implications, and clear applications for human contraception and infertility inherent in understanding the mechanisms by which egg and sperm meet, these are still poorly understood. On page 1029 of this issue, Herberg et al. (1) investigate fertilization in zebrafish and identify Bouncer, a protein that is important for sperm-egg interaction and also creates a species-specific barrier. This discovery takes us a step closer to understanding species-specific fertilization and species evolution.