Research

Evolution of cytoplasmic sex determination


Multicellular organisms have been continuously involved in complex interactions with microorganisms during their evolution, the most intimate of which is endosymbiosis, a type of symbiosis in which a microbial partner lives within its host cells. Endosymbiosis has played a key role in the emergence of major life forms on Earth and in the generation of biological diversity. However, appreciation of endosymbiosis as an important source of evolutionary novelty has developed relatively recently. Over the past years, evidence has been accumulating that endosymbionts affect animal biology in many ways, such as host nutrition and development, defense against natural enemies and immunity. We investigate another critical evolutionary process influenced by microbial endosymbionts: the mechanisms of sex determination of their eukaryotic hosts (for a review, see Cordaux et al. 2011, Trends in Genetics).

Sex determination is one of the most fascinating developmental pathways in metazoans. It governs sexual differentiation and it is both evolutionarily ancient and ubiquitous. In animals, sexual differences between males and females are usually determined by chromosomal sex factors, commonly carried by sex chromosomes. Sex determination can also be affected by inherited microbial endosymbionts, a phenomenon known as cytoplasmic sex determination. Disrupting the mode of sex determination of their hosts in favor of females may be advantageous for endosymbionts because these intracellular microorganisms are predominantly transmitted vertically through female egg cytoplasm, not male sperm. We study the evolution of cytoplasmic sex determination using the fascinating system involving terrestrial isopods (pillbugs) and their bacterial endosymbionts Wolbachia (for a review, see Cordaux and Gilbert 2017, Genes). We recently showed that the horizontal transfer of a Wolbachia genome into the nuclear genome generated a novel W sex chromosome in the common pillbug Armadillidium vulgare (see figure below, from Leclercq et al. 2016, PNAS).

Our research on the evolution of cytoplasmic sex determination is funded by:

  • ERC Starting Grant EndoSexDet 2011-2015 (PI: Richard Cordaux)

  • PEPS CNRS MicroFem 2015 (PI: Richard Cordaux)

  • ANR CytoSexDet 2016-2021 (PI: Richard Cordaux)

  • Région Nouvelle-Aquitaine 2020-2023 (PI: Jean Peccoud)

  • ANR SymChroSex 2021-2025 (PI: Jean Peccoud)

  • ANR RESIST 2022-2026 (PI: Richard Cordaux)

Evolution of transposable elements


Transposable elements (TEs), also known as jumping genes, are pieces of DNA that can move within and, sometimes, between genomes. They exist in a large diversity of structures and types, and they are very frequent in both eukaryote (as exemplified by the human genome, at least half of which is composed of TEs) and prokaryote (as exemplified by Wolbachia bacterial endosymbionts) genomes. During the past years, TEs have been shown to be one of the major forces that drive genome evolution in all living organisms, from generating insertion mutations and genomic instability to altering gene expression and contributing to genetic innovation. In this context, we study the evolution of TEs in prokaryotes and eukaryotes by focussing on two major directions: their evolutionary dynamics and their genomic impact.

A recent area of emphasis in our research on TEs has been on horizontal transfer. Horizontal transfer of genetic material is the transmission of DNA between organisms by means other than parent-to-offspring inheritance. It is pivotal to the biology and evolution of prokaryotes and is increasingly recognized as an important factor in the evolution of eukaryotes. TEs are particularly prone to horizontal transfer between genomes (Peccoud et al. 2017, PNAS); however the vectors of horizontal transfer are poorly known. We investigate the mechanisms and frequency of horizontal transfer of TEs in particular, and genetic material in general, mediated by viruses (for a review, see Gilbert and Cordaux 2017, Curr. Opin. Virol.), using population genomics approaches (see figure below, from Gilbert et al. 2014, Nature Communications).

Our research on the evolution of transposable elements is funded by:

  • CNRS Young Investigator ATIP Grant 2008-2010 (PI: Richard Cordaux)

  • ANR TransVir 2015-2021 (PI: Clément Gilbert)