Topic
Dosage compensation
About: Dosage compensation is a research topic. Over the lifetime, 1920 publications have been published within this topic receiving 124589 citations.
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TL;DR: The potential evolutionary relationship between X chromosome inactivation and imprinting is explored by focusing on two noncoding RNAs involved in these processes, Xist and H19, an imprinted RNA on chromosome 7.
Abstract: Mammals exhibit two epigenetic phenomena whose consequence is the silencing of one of two wild-type copies of a gene X chromosome inactivation in females and parental imprinting of selected autosomal genes. As the mechanisms underlying these forms of gene dosage control are being elucidated, some striking similarities between them are being revealed. Of these similarities, none is more curious than the involvement of two noncoding RNAs in these processes, Xist, in the case of X chromosome inactivation, and H19, an imprinted RNA on chromosome 7. This article will explore the potential evolutionary relationship between X chromosome inactivation and imprinting by focusing on these unusual RNAs.
53 citations
TL;DR: It is concluded that the evolutionary conservation of the chain in monotremes, the structural properties of the translocated chromosomes and the highly accurate segregation at meiosis make the platypus system remarkably different from meiotic multiples in other species.
Abstract: The duck-billed platypus is an extraordinary mammal. Its chromosome complement is no less extraordinary, for it includes a system in which ten sex chromosomes form an extensive meiotic chain in males. Such meiotic multiples are unprecedented in vertebrates but occur sporadically in plant and invertebrate species. In this paper, we review the evolution and formation of meiotic multiples in plants and invertebrates to try to gain insights into the origin of the platypus meiotic multiple. We describe the meiotic hurdles that translocated mammalian chromosomes face, which make longer chains disadvantageous in mammals, and we discuss how sex chromosomes and dosage compensation might have affected the evolution of sex-linked meiotic multiples. We conclude that the evolutionary conservation of the chain in monotremes, the structural properties of the translocated chromosomes and the highly accurate segregation at meiosis make the platypus system remarkably different from meiotic multiples in other species. We discuss alternative evolutionary models, which fall broadly into two categories: either the chain is the result of a sequence of translocation events from an ancestral pair of sex chromosomes (Model I) or the entire chain came into being at once by hybridization of two populations with different chromosomal rearrangements sharing monobrachial homology (Model II).
53 citations
TL;DR: In vivo mobility experiments demonstrate that SAF-A is a component of a highly stable proteinaceous structure in the territory of inactive X chromosomes, which might act as a platform for immobilizing Xist RNA during the maintenance phase of X inactivation.
53 citations
TL;DR: The authors used expression data from the chicken (Gallus gallus) to show that duplicated genes known to be dosage-sensitive are preferentially dosage-compensated on the chicken Z chromosome, even in the absence of a complete and chromosome wide dosage compensation mechanism.
Abstract: In many diploid species, sex determination is linked to a pair of sex chromosomes that evolved from a pair of autosomes. In these organisms, the degeneration of the sex-limited Y or W chromosome causes a reduction in gene dose in the heterogametic sex for X- or Z-linked genes. Variations in gene dose are detrimental for large chromosomal regions when they span dosage-sensitive genes, and many organisms were thought to evolve complete mechanisms of dosage compensation to mitigate this. However, the recent realization that a wide variety of organisms lack complete mechanisms of sex chromosome dosage compensation has presented a perplexing question: How do organisms with incomplete dosage compensation avoid deleterious effects of gene dose differences between the sexes? Here we use expression data from the chicken (Gallus gallus) to show that ohnologs, duplicated genes known to be dosage-sensitive, are preferentially dosage-compensated on the chicken Z chromosome. Our results indicate that even in the absence of a complete and chromosome wide dosage compensation mechanism, dosage-sensitive genes are effectively dosage compensated on the Z chromosome.
53 citations
TL;DR: The conservation of some escape genes across multiple species and the ability of the mouse inactive X to recapitulate human escape status both suggest that escape from XCI is controlled by conserved processes.
Abstract: Sex chromosomes originate as a pair of homologus autosomes that then follow a general pattern of divergence. This is evident in mammalian sex chromosomes, which have undergone stepwise recombination suppression events that left footprints of evolutionary strata on the X chromosome. The loss of genes on the Y chromosome led to Ohno's hypothesis of dosage equivalence between XY males and XX females, which is achieved through X-chromosome inactivation (XCI). This process transcriptionally silences all but one X chromosome in each female cell, although 15-30% of human X-linked genes still escape inactivation. There are multiple evolutionary pathways that may lead to a gene escaping XCI, including remaining Y chromosome homology, or female advantage to escape. The conservation of some escape genes across multiple species and the ability of the mouse inactive X to recapitulate human escape status both suggest that escape from XCI is controlled by conserved processes. Evolutionary pressures to minimize dosage imbalances have led to the accumulation of genetic elements that favor either silencing or escape; lack of dosage sensitivity might also allow for the escape of flanking genes near another escapee, if a boundary element is not present between them. Delineation of the elements involved in escape is progressing, but mechanistic understanding of how they interact to allow escape from XCI is still lacking. Although increasingly well-studied in humans and mice, non-trivial challenges to studying escape have impeded progress in other species. Mouse models that can dissect the role of the sex chromosomes distinct from sex of the organism reveal an important contribution for escape genes to multiple diseases. In humans, with their elevated number of escape genes, the phenotypic consequences of sex chromosome aneuplodies and sexual dimorphism in disease both highlight the importance of escape genes.
53 citations