A widely employed germ cell marker is an ancient disordered protein with reproductive functions in diverse eukaryotes

Sex allows two individuals of a species to combine their genetic information and generate new offspring. As such, and unlike most of the cells that make up an organism, reproductive cells carry DNA that will be passed to the next generation. To prepare for sexual reproduction, reproductive cells undergo a process whereby they give up half of their DNA. Moreover, in many species, reproductive cells undergo dramatic changes in size and shape to become specialized as eggs or sperm. For two decades, research scientists have made use of an antibody that specifically targets and labels reproductive cells in mice and rats, long before they become recognizable as sperm or eggs. However, nothing was known about the protein that this antibody recognizes. Now, Carmell et al. have found that the antibody recognizes a protein called GCNA. This protein was previously thought to be limited to mice and rats. However, GCNA is in fact a member of a far-flung family of proteins that had gone unnoticed by researchers due to their unusual composition and large unstructured regions. Carmell et al. show that this protein family extends beyond rodents and even mammals, and actually exists in all branches of eukaryotic life, including plants and single-celled organisms. In most species examined, the genes encoding these proteins are most active in reproductive cells. The most important next step is to figure out precisely what GCNA proteins are doing in reproductive cells. This will also hopefully explain why these proteins appear to have been conserved for more than 2 billion years, throughout the entire history of eukaryotes.