Dr. Quentin Helleu

I am interested in understanding the molecular basis and evolutionary impacts of selfish genetic elements.
My graduate research, under the supervision of Dr. Catherine Montchamp-Moreau, were focused on a segregation distorter spreading in populations of the fruit fly Drosophila simulans:
Segregation distorters are selfish genetic elements that promote their own transmission by subverting the meiotic process to their advantage. The spread of an X-linked distorter (Sex Ratio) in populations results in an excess of females, which triggers a genetic conflict between the X chromosome and the rest of the genome. Such conflicts are important drivers of genome evolution, but little is known about the molecular nature and the function of the Sex Ratio selfish elements. In the Paris Sex Ratio system of Drosophila simulans, two distorter elements on the X chromosome co-operate to prevent Y chromosome sister chromatids segregation during meiosis II. The aim of my PhD project was to identify one of the two X-linked elements. First I used two mapping approaches to reduce the number of candidate genes: recombination and natural polymorphism (association mapping). Then, I precociously analyzed the molecular evolution and gene expression of the candidate genes. Finally, I built genetically modified lines to functionally identify the segregation distorter. The identified genetic element, HP1D2, is a young rapidly evolving gene which encodes a heterochromatin packaging protein. Using a tagged version of the protein I showed that HP1D2 directly interacts with the Y chromosome in spermatogonia.
My present research is focused on the molecular basis and evolution of Greenbeard genes in the fire ant Solenopsis invicta:
Greenbeard genes are selfish genetic elements that favor their own transmission by increasing the fitness of other carrying individuals. Such a phenotype, can only occur if a gene or a group of tightly linked genes produce (1) a conspicuous phenotype, (2) the ability to recognize this phenotype, allowing the bearer individual to discriminate carriers from non-carriers and (3) a nepotistic behavior in favor of carriers. These extraordinary selfish genetic elements can have profound evolutionary consequences on genomes and social behavior. The first identified Greenbeard haplotype was in the fire ant Solenopsis invicta. In this species, the Social b (Sb) supergene, an 13 Mb non-recombining region is associated with a Greenbeard effect. Discriminating on cuticular chemical profiles, carrier ant workers spread the Sb supergene by killing non-bearer queens. In this project I aim to study the molecular evolution of this Y-like social chromosome.


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