Characterizing the chromosomes of the Australian model marsupial Macropus eugenii (tammar wallaby)

Alsop, Amber E.; Miethke, Pat; Rofe, Ruth; Koina, Edda; Sankovic, Natasha; Deakin, Janine E.; Haines, Helen; Rapkins, Robert W.; Graves, Jennifer A. Marshall

doi:10.1007/s10577-005-0989-2

Cited by 49 publications

(69 citation statements)

References 22 publications

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“…2Bd) (>90% of metaphases). This difference could merely reflect the different degrees of chromosome condensation reported previously for the marsupial active and inactive X chromosomes (Graves 1967), and apparent from comparisons of the DAPI staining of the two female X chromosomes (see Alsop et al 2005). Line scans of intensities of both DAPI and H3K27me3 signals showed that indeed the X chromosome appearing to be slightly enriched in H3K27me3 showed also a slight increase in DAPI intensity (Fig.…”

Section: Histone H3 Trimethylation Of Lysine 27 (H3k27me3)mentioning

confidence: 67%

“…The X chromosome is the only small submetacentric chromosome, and is easily distinguished by its morphology and the prominent interstitial nucleolus organizer region (NOR) on its short arm (Alsop et al 2005). The C-band positive short arm of the X (Xp) consists of sequences shared with the Y chromosome, which were added relatively recently to both sex chromo- somes (Toder et al 1997).…”

Section: Resultsmentioning

confidence: 99%

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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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Section: Histone H3 Trimethylation Of Lysine 27 (H3k27me3)mentioning

confidence: 67%

Section: Resultsmentioning

confidence: 99%

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

et al. 2009

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“…Hybridization and detection were carried out following the procedure described by Alsop et al (2005). Images were captured and enhanced using IPLab software (Scanalytics Inc.).…”

Section: Fluorescence In Situ Hybridization (Fish)mentioning

confidence: 99%

Bird-like sex chromosomes of platypus imply recent origin of mammal sex chromosomes

Veyrunes¹,

Waters²,

Miethke³

et al. 2008

Genome Res.

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In therian mammals (placentals and marsupials), sex is determined by an XX female: XY male system, in which a gene (SRY) on the Y affects male determination. There is no equivalent in other amniotes, although some taxa (notably birds and snakes) have differentiated sex chromosomes. Birds have a ZW female: ZZ male system with no homology with mammal sex chromosomes, in which dosage of a Z-borne gene (possibly DMRT1) affects male determination. As the most basal mammal group, the egg-laying monotremes are ideal for determining how the therian XY system evolved. The platypus has an extraordinary sex chromosome complex, in which five X and five Y chromosomes pair in a translocation chain of alternating X and Y chromosomes. We used physical mapping to identify genes on the pairing regions between adjacent X and Y chromosomes. Most significantly, comparative mapping shows that, contrary to earlier reports, there is no homology between the platypus and therian X chromosomes. Orthologs of genes in the conserved region of the human X (including SOX3, the gene from which SRY evolved) all map to platypus chromosome 6, which therefore represents the ancestral autosome from which the therian X and Y pair derived. Rather, the platypus X chromosomes have substantial homology with the bird Z chromosome (including DMRT1) and to segments syntenic with this region in the human genome. Thus, platypus sex chromosomes have strong homology with bird, but not to therian sex chromosomes, implying that the therian X and Y chromosomes (and the SRY gene) evolved from an autosomal pair after the divergence of monotremes only 166 million years ago. Therefore, the therian X and Y are more than 145 million years younger than previously thought.

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“…Since we already had information about X-borne genes, a start was made with the tammar X and Chromosome 5 (Alsop et al 2005), but this was slow going.…”

Section: The Boden Conference and The Kangaroo Genome Centrementioning

confidence: 99%

Kangaroo gene mapping and sequencing: insights into mammalian genome evolution

Graves

2013

Aust. J. Zool.

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Abstract. The deep divergence of marsupials and eutherian mammals 160 million years ago provides genetic variation to explore the evolution of DNA sequence, gene arrangement and regulation of gene expression in mammals. Following the pioneering work of Professor Desmond W. Cooper, emerging techniques in cytogenetics and molecular biology have been adapted to characterise the genomes of kangaroos and other marsupials. In particular, genetic and genomic work over four decades has shown that marsupial sex chromosomes differ significantly from the eutherian XY chromosome pair in their size, gene content and activity. These differences can be exploited to deduce how mammalian sex chromosomes, sex determination and epigenetic silencing evolved.

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Characterizing the chromosomes of the Australian model marsupial Macropus eugenii (tammar wallaby)

Cited by 49 publications

References 22 publications

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

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

Bird-like sex chromosomes of platypus imply recent origin of mammal sex chromosomes

Kangaroo gene mapping and sequencing: insights into mammalian genome evolution

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