The selfish genes that kill sex cells
Genes that produce both a poison and an antidote may help to drive the evolution of new species.
During evolution, new species emerge when individuals from different populations of similar organisms no longer breed with each other, or when the offspring produced if they do breed are sterile. This process is known as “reproductive isolation” and, for over 100 years, evolutionary biologists have tried to better understand how this process happens.
Animals, plants and fungi produce sex cells — known as gametes — when they are preparing to reproduce. These cells are made when cells containing two copies of every gene in the organism divide to produce new cells that each only have one copy of each gene. Therefore, a particular gene copy usually has a 50% chance of being carried by an individual gamete. There are some genes that selfishly increase their chances of being transmitted to the next generation by destroying the gametes that do not carry them. These “gamete killer” genes reduce the fertility of the organism and lead to reproductive isolation.
Fission yeast is a fungus that is widely used in research. There are different strains of fission yeast that are reproductively isolated from each other, but it is not known whether gamete killers are responsible for this isolation. To address this question, Wen Hu and colleagues investigated the causes of reproductive isolation in fission yeast.
The experiments identified two gamete killers, referred to as cw9 and cw27. Both genes belong to the wtf gene family. Each gene is believed to encode two different proteins, one that acts as a poison and one that acts as an antidote. The poison is capable of killing all gametes, but the antidote protects the cells that contain the gamete killer gene. Further experiments show that the antidote produced by one of the gamete killer genes cannot protect cells against the poison produced by the other gene.
A separate study by Nicole Nuckolls, María Bravo Núñez and colleagues found that another member of the wtf family known as wtf4 also acts as a gamete killer in fission yeast. The experiments show that, like cw9 and cw27, wtf4 also produces both a poison and an antidote to selectively kill the gametes that don’t carry it.
Together, these findings shed new light on the causes of reproductive isolation, and will contribute to deeper understanding of speciation and evolution in general. Furthermore, these studies may guide the search for gamete killers in humans and other organisms. In the future, gamete killers could potentially be used to eradicate populations of pests that damage crops or spread diseases in humans.
To find out more
Read the eLife research papers on which this eLife digest is based: “A large gene family in fission yeast encodes spore killers that subvert Mendel’s law” (June 20, 2017) and “wtf genes are prolific dual poison-antidote meiotic drivers” (June 20, 2017).
Read a commentary on these research papers: “Heredity: The gene family that cheats Mendel”.
