A collaborative study by researchers at Stowers Institute for Medical Research and Fred Hutchinson Cancer Research Center reports an exceptional genetic survival strategy of wtf4 gene. The respective study appeared in the journal eLife in 2017. It highlights how the wtf4 gene found in S. kambucha fission yeast acts as both a poison and an antidote, ensuring its transmission into the next generation, and to eliminate its competition.
Wtf genes, also known as selfish genes, are parasitic in nature. Their main function is to survive and spread. Particularly, the wtf4 gene is a meiotic drive selfish gene which interferes with the process of meiosis.
Meiosis is the form of cell division that creates sex cells, called gametes, like eggs and sperm. Gametes contain only one copy of each chromosome. However, the cells that generate gametes contain two copies, one from each parent. Meiosis ensures equal distribution of chromosomes to the gametes. For example, males with an X and Y chromosome produce 50 percent X-bearing and 50 percent Y-bearing sperm.
The meiotic drive genes stack the odds in their favor by destroying the gametes that don’t carry them. For example, if the male has a gamete-killing meiotic drive gene on his X chromosome, the sperm carrying the Y chromosome are killed. It this way, the competition to fertilize the egg reduces to half. In this case, wtf genes poison their prey.
The dual role of wtf genes
Wtf selfish genes act as a poison to all the developing gametes. However, they keep the title “antidote” for themselves as well. The gametes inheriting the selfish genes, when exposed to the poison, don’t succumb to it. This is because they have the antidote. On the other hand, the gametes that don’t inherit the selfish gene are destroyed.
In a 2014 study, the researchers discovered the actions of multiple independent meiotic drivers in fission yeasts. However, they were unaware of the responsible genes and how they destroyed gametes that didn’t inherit the genes. In order to learn more, the research team used genetic mapping to reveal the complex landscape of multiple meiotic drive genes on chromosome 3 of S. kambucha.
It was found that wtf genes made two different RNA messages,
- A short message which encodes the poison
- A long message which encodes the antidote
The cells were imaged during meiosis with the poison protein tagged green and the antidote protein tagged red. The research team observed the poison everywhere in the image. This might mean that every cell was exposed to the poison however; the antidote was present only in the spores that inherited the wtf gene. Resultantly, the gametes lacking the wtf genes died.
The combination of the genetics experiments and imaging studies provide plentiful evidence that wtf genes make both a poison and antidote. Moreover, the researchers also found that wtf4 is a member of a large family of selfish genes. Their findings are specifically interesting from an evolutionary perspective.
The wtf genes make a poison that potentially kills everything, including them. On the other hand, their role as an antidote is the way they figured out how to selectively eliminate their competition. The study expands the current understanding of the nature of gamete-killing meiotic drive genes. The findings may also guide future discoveries of meiotic drive genes in other organisms, such as crops or humans.