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Thesis defense: Corentin Dechaud

When May 18, 2021
from 02:00 to 05:00
Where visio
Contact Name
Attendees Jury members:
Susana Coelho - Directrice de recherche Max Planck Institute Tübingen - Rapportrice;
Hadi Quesneville - Directeur de recherche INRAE Versailles - Rapporteur;
Anna-Sophie Fiston-lavier - Maître de conférences Univ. de Montpellier - Examinatrice;
Clément Gilbert - Chargé de recherche CNRS Paris-Saclay - Examinateur;
Manfred Schartl - Professeur Univ. Würzburg - Examinateur;
Cristina Vieira - Professeur Univ. Lyon 1 - Examinatrice;
Jean-Nicolas Volff - Professeur ENS de Lyon - Directeur de thèse;
Magali Maussion-Naville - Agrégée préparatrice ENS de Lyon - Co-encadrante.
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On may 18th, Corentin Dechaud of the team of Jean-Nicolas Volff will support his thesis entitled: 


"Impact of transposable elements on the evolution of gene expression: example of sex in teleost fish" 


In teleost fish, sexual reproduction and sexual gene regulatory networks are highly variable. In gonochoristic species, sex is determined either environmentally or genetically and can involve different genes depending on the species investigated. Sexual development and maintenance appear also variable in this clade.

To understand the origin of this diversity, I studied the posssible impact of transposable elements on the fast evolution of gene regulatory networks related to sex in fish. Transposable elements are endogenous DNA sequences able to move or copy themselves in genomes. Even if they are often deleterious for their host, transposable elements can also carry regulatory sequences, such as transcription factor binding sites, and spread them in genomes. Their diversity in  fish genomes form a source of ready-to-use regulatory sequences potentially involved in the fast evolution of some gene regulatory networks.

To test this hypothesis, I used RNA sequencing data from male and female gonads of the Japanese Medaka, \textitOryzias latipes. First I analysed gene and transposable element expression and discovered regions of the genome enriched in sex-biased genes associated to sex-biased transposable elements. Moreover, genes and transposable elements located close on chromosomes tend to present similar expression bias between testis and ovary. Two hypothesis that are not mutually exclusive can explain this observation : either transposable element influence gene expression of neighbooring genes, or the genomic locus where the transposable element inserts influence its expression. We were not able to definitively discriminate between these two hypotheses, but our work identified several clues for a regulatory role of transposable elements. In the second part and in a complementary way I found transposable element families physically enriched near to sex-biased genes. One family was further investigated and shown to carry transcription factor binding sites involved in sexual function.

This work brings new insights on the possible role of transposable elements in the fast evolution of gene regulatory networks and paves the way for future functional studies.

The defense will be in english.