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Diversity of X-chromosome inactivation patterns during early mammalian development

Abstract : X-chromosome inactivation ensures dosage compensation for Xlinked gene products in mammals. In eutherians, X inactivation is controlled by the non-coding Xist transcript and is usually random, with either the paternal or maternal X being chosen for silencing. In marsupials, which have no Xist gene, X inactivation is subject to imprinting, with non-random inactivation of the paternal Xp chromosome in all cells. Despite showing random X inactivation in their somatic cells, rodents do in fact display imprinted X inactivation during early development and in extra-embryonic tissues. This early, imprinted form of X inactivation in rodents appears to be due to imprinted Xist expression. The pattern of Xist expression and X inactivation during the early development of other eutherians remains unclear. Indeed the degree to which X inactivation is conserved between mammals remains an open question. We have investigated this process during early rabbit embryogenesis and find that the kinetics and monoallelic regulation of X inactivation are very different between rabbits and mice. Our results suggest that an imprinted form of X inactivation may have evolved more than once during the course mammalian evolution, first in marsupials, through an unknown mechanism; and later in some eutherians, such as rodents, via an Xist imprint. This provides evidence for remarkable evolutionary diversity in the mechanisms underlying dosage compensation mechanisms between mammals.
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Ikuhiro Okamoto, Véronique Duranthon, Dominique Thépot, Nathalie Peynot, Jean Paul Renard, et al.. Diversity of X-chromosome inactivation patterns during early mammalian development. 68. Annual Meeting of the Society for Developmental Biology, Jul 2009, San Francisco, United States. ⟨10.1016/j.ydbio.2009.05.035⟩. ⟨hal-02751161⟩



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