Late DNA Replication in the Paternally Derived X Chromosome of Female Kangaroos

Sharman, G. B.

doi:10.1038/230231a0

Cited by 227 publications

(133 citation statements)

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“…Genomic imprinting is a process whereby the expression of an allele depends on whether it is derived from the mother or father (Bartolomei and Tilghman 1997;Verona et al 2003). Genomic imprinting was first discovered on the X chromosome, where Sharman and colleagues (Richardson et al 1971;Sharman 1971) described a form of XCI in marsupials in which the paternal X chromosome is preferentially silenced. Other than in mammals, genomic imprinting has also been identified in angiosperm plants and in a few insects (Braidotti et al 2004).…”

Section: Roles Of Ncrnas In Genomic Imprinting: One Is Enoughmentioning

confidence: 99%

Eukaryotic regulatory RNAs: an answer to the ‘genome complexity’ conundrum

Prasanth¹,

Spector²

2007

Genes Dev.

365

305

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A large portion of the eukaryotic genome is transcribed as noncoding RNAs (ncRNAs). While once thought of primarily as "junk," recent studies indicate that a large number of these RNAs play central roles in regulating gene expression at multiple levels. The increasing diversity of ncRNAs identified in the eukaryotic genome suggests a critical nexus between the regulatory potential of ncRNAs and the complexity of genome organization. We provide an overview of recent advances in the identification and function of eukaryotic ncRNAs and the roles played by these RNAs in chromatin organization, gene expression, and disease etiology.

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Section: Roles Of Ncrnas In Genomic Imprinting: One Is Enoughmentioning

confidence: 99%

Eukaryotic regulatory RNAs: an answer to the ‘genome complexity’ conundrum

Prasanth¹,

Spector²

2007

Genes Dev.

365

305

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“…Perhaps the most dramatic difference is that marsupial XCI is imprinted, as it is the paternal X chromosome that is always the inactivate one (Cooper 1971;Sharman 1971), whereas inactivation is random in placental mammals. The subsequent discovery that paternal X inactivation also occurred during the first stages of rodent development and was retained in rodent extraembryonic tissues (Takagi and Sasaki 1975;Huynh and Lee 2003;Okamoto et al 2004) suggests imprinted XCI in marsupials may represent a simpler ancestral inactivation mechanism that evolved into a more complex and random process in placental embryos.…”

mentioning

confidence: 99%

“…As for humans and mice, the marsupial inactive X replicates late in S phase (Graves 1967;Sharman 1971) and sex chromatin has been observed, though inconsistently, in some species and tissues (VandeBerg et al 1987). Differential histone H4 underacetylation has also been demonstrated between the two X chromosomes in cells from female marsupials (Wakefield et al 1997), but no DNA methylation differences have been detected (Piper et al 1993;Loebel and Johnston 1996).…”

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confidence: 99%

Specific patterns of histone marks accompany X chromosome inactivation in a marsupial

et al. 2009

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The inactivation of one of the two X chromosomes in female placental mammals represents a remarkable example of epigenetic silencing. X inactivation occurs also in marsupial mammals, but is phenotypically different, being incomplete, tissuespecific and paternal. Paternal X inactivation occurs also in the extraembryonic cells of rodents, suggesting that imprinted X inactivation represents a simpler ancestral mechanism. This evolved into a complex and random process in placental mammals under the control of the XIST gene, involving notably variant and modified histones. Molecular mechanisms of X inactivation in marsupials are poorly known, but occur in the absence of an XIST homologue. We analysed the specific pattern of histone modifications using immunofluorescence on metaphasic chromosomes of a model kangaroo, the tammar wallaby. We found that all active marks are excluded from the inactive X in marsupials, as in placental mammals, so this represents a common feature of X inactivation throughout mammals. However, we were unable to demonstrate the accumulation of inactive histone marks, suggesting some fundamental differences in the molecular mechanism of X inactivation between marsupial and placental mammals. A better understanding of the epigenetic mechanisms underlying X inactivation in marsupials will provide important insights into the evolution of this complex process.

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“…The random form of XCI is observed in somatic tissues of eutherian mammals such as humans and mice. In 1971, Sharman and colleagues documented one of the earliest examples of genomic imprinting in mammals when they described a form of XCI in which the paternal X chromosome (X P ) is preferentially silenced (Sharman 1971). Imprinted XCI takes place in the extraembryonic tissues of some eutherians such as the rodent (Takagi and Sasaki 1975) and cow (Xue et al 2002).…”

Section: Two Forms Of X-chromosome Inactivation In the Mousementioning

confidence: 99%