X inactivation in a mammal species with three sex chromosomes

Frederic Veyrunes (1) , Julie Perez (1)

1 UMR ISEM - Institut des Sciences de l'Evolution de Montpellier

X inactivation is a fundamental mechanism in eutherian mammals to restore a balance of X-linked gene products between XY males and XX females. However, it has never been extensively studied in a eutherian species with a sex determination system that deviates from the ubiquitous XX/XY. In this study, we explore the X inactivation process in the African pygmy mouse Mus minutoides, that harbours a polygenic sex determination with three sex chromosomes: Y, X, and a feminizing mutant X, named X*; females can thus be XX, XX*, or X*Y, and all males are XY. Using immunofluorescence, we investigated histone modification patterns between the two X chromosome types. We found that the X and X* chromosomes are randomly inactivated in XX* females, while no histone modifications were detected in X*Y females. Furthermore, in M. minutoides, X and X* chromosomes are fused to different autosomes, and we were able to show that the X inactivation never spreads into the autosomal segments. Evaluation of X inactivation by immunofluorescence is an excellent quantitative procedure, but it is only applicable when there is a structural difference between the two chromosomes that allows them to be distinguished.

Domaines: Organisation et fonctions cellulaires [q-bio.SC]; Evolution [q-bio.PE]

Frederic Veyrunes, Julie Perez. X inactivation in a mammal species with three sex chromosomes. Chromosoma, 2018, 127 (2), pp.261-267. ⟨10.1007/s00412-017-0657-2⟩. ⟨hal-02353212⟩