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Genetic Conflict: Types of Proteins in Meiotic Drive Systems

As a biologist, Christina loves exploring the sciences and applying them to everyday life.

Overreplication and Polymerases

The kinds of protein in a meiotic drive system is potentially dependent on the type of meiotic drive. One type of drive is overreplication, where the selfish element creates more copies compared to other genes in the same organism. Overreplication is frequently used by transposable elements, short DNA sequences that can change their position through the genome. Transposable elements can either use their own promoter or use a promoter from their host or another transposable element to replicate themselves. Transposable elements can also utilize reverse transcriptase or helicase, making proteins related to replication and transcription essential to their drive systems. As a result, protein classes like polymerases would be expected in an overreplication drive system.

Gonotaxis And Chromobox Proteins

In contrast to overreplication, gonotaxis is a meiotic drive system focusing on replicating only in the germ line and not somatic cells. By doing this, genes will then be inherited by more than half of the gametes. Gonotaxis is especially prevalent in female meiosis. By replicating only in the egg and not any of the polar bodies created in female meiosis, selfish genes can replicate themselves in more than half of the gametes. To combat selfish genes in gonotaxis, a class of small non-coding RNA called piwi-interacting RNA (piRNA) regulates genes in the germ line. Specifically, in Drosophila melanogaster, piRNA utilizes heterochromatin-binding proteins to regulate the germ line (Courret) by marking the selfish genes for methylation, silencing them. Heterochromatin-binding proteins are members of the protein class chromobox family proteins (Lomberk). As a result, it can be assumed that chromobox proteins are utilized by gonotaxis meiotic drive systems.

Interference: Poison- Antidote Systems

Focusing on a particular type of interference system, there are loci that codes for two separate proteins, one having a poison and the other having an antidote. During gametogenesis, the selfish element stays in gametes with the antidote while the poison acts on all of the gametes (Eichbush). This results in only gametes containing both the poison and the antidote being viable. The genes coding for the poison and the antidote must be close together to minimize recombination separating the poison and antidote.

This poison interference system is observed in the wtf gene family (Hernandez). This family contains long terminal repeats of the Tf transposons (Hernandez). Specifically, wtf4 codes for both the poison and the antidote (Hernandez), as the shorter transcript for the poison overlaps with the longer transcript for the antidote (Hu). One of the things the wtf genes codes for are transmembrane proteins. These transmembrane proteins can kill cells by damaging the cell membrane integrity (Hu). The antidote inhibits the poison’s ability to damage the membrane, allowing for only gametes with only the antidote to survive. Due to the reliance on these transmembrane proteins in this poison-antidote system, making proteins essential for transcription vital to the drive system’s success. As a result, the proteins likely to be present in interference meiotic drive systems are proteins like the Sp1 transcription factor.

Interference: Parental Genetic Elimination

Another type of an interference meiotic drive system is parental genetic elimination, in which one parent’s genome is either partially or completely blocked or removed from the gamete. Parental genetic elimination requires parental sex ratio (PSR) genes (Bendetta). Due to the role of PSR genes in parental genetic elimination, one can assume PSR genes also contribute to interference systems. Eliminating or limiting the contribution of one of the parents’ genetic material is necessary to affect the sex ratio. For example, in androgenesis, the maternal genome is eliminated, allowing the male genome to use the egg for cloning.

This manipulation of the sex ratio can be categorized as a case of interference. Parental genetic elimination requires elimination or limitation of a parental genome, which is similar to the elimination of gametes with only an interference poison.

RNA Interference

RNA interference (RNAi) can be used to test the role in the proteins in each drive system. RNAi turns off specific genes by making doubled stranded DNA segments of the target DNA. The enzyme Dicer then binds to these double stranded segments. Dicer then facilitates an Arogenate protein silencing the gene via RNA cleavage or other methods. By inserting double stranded genes of a particular protein in RNAi, that protein wouldn’t be able to be transcribed due to the silenced genes. As a result, the role of particular proteins in drive systems can be tested through RNAi.

Comparing the amount of drive occurring in one control population to another population with RNAi on the target genes will reveal if those genes truly contribute to meiotic drive. For interference systems, the target genes are the transmembrane proteins and transcription factors like Sp1, and in gonotaxis the target genes are chromobox proteins. If the hypothesis is true, there will be more interference observed in the population without RNAi. PiRNA naturally combat the selfishness of transposons, making the silencing of transposons via piRNA a very effective tool in this experiment.

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Selfish genetic elements use varying methods to cheat meiosis based on their drive system. As a result, proteins that are used in a drive system are also dependent on the type of drive system. Polymerases are likely a major protein class in overreplication due to their essential role in replication. In contrast, chromobox proteins are more likely to be part of gonotaxis drive systems due to being heterochromain-binding proteins. Interference systems, like parental genetic elimination and poison-antidote systems, use transcription factors like Sp1 due to the crucial role of transcription in interference systems. RNAi interference can be used to test the hypothesis of the essential roles of these proteins in each drive system.

Works Cited

Eickbush, M. T., Young, J. M., & Zanders, S. E. (2019). Killer meiotic drive and dynamic evolution of the wtf gene family. Molecular Biology and Evolution, 36(6), 1201-1214.

López Hernández, JF, Zanders, SE. Veni, vidi, vici: the success of wtf meiotic drivers in fission yeast. Yeast. 2018; 35: 447– 453.

Hermant C, Torres-Padilla ME. TFs for TEs: the transcription factor repertoire of mammalian transposable elements. Genes Dev. 2021 Jan 1;35(1-2):22-39. doi: 10.1101/gad.344473.120. PMID: 33397727; PMCID: PMC7778262.

Dalla Benetta, E., Antoshechkin, I., Yang, T., Nguyen, H. Q. M., Ferree, P. M., & Akbari, O. S. (2020). Genome elimination mediated by gene expression from a selfish chromosome. Science advances, 6(14), eaaz9808.

Courret C, Chang C-H, Wei KH-C, Montchamp-Moreau C, Larracuente AM. 2019 Meiotic drive mechanisms: lessons from Drosophila. Proc. R. Soc. B 286: 20191430.

Fouvry, L., Ogereau, D., Berger, A., Gavory, F., & Montchamp-Moreau, C. (2011). Sequence analysis of the segmental duplication responsible for Paris sex-ratio drive in Drosophila simulans. G3: Genes| Genomes| Genetics, 1(5), 401-410.

Lomberk, G., Wallrath, L. & Urrutia, R. The Heterochromatin Protein 1 family. Genome Biol 7, 228 (2006).

Hu, W., Jiang, Z. D., Suo, F., Zheng, J. X., He, W. Z., & Du, L. L. (2017). A large gene family in fission yeast encodes spore killers that subvert Mendel’s law. Elife, 6, e26057.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2022 Christina Garvis

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