The monotreme genome: a patchwork of reptile, mammal and unique features?

Grützner, Frank; Deakin, Janine E.; Rens, Willem; El‐Mogharbel, Nisrine; Graves, Jennifer A. Marshall

doi:10.1016/j.cbpb.2003.09.014

Cited by 40 publications

(34 citation statements)

References 86 publications

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“…These findings reinforce the distinct phylogenetic positions of marsupials and monotremes within the vertebrate and mammalian radiations (12,13). In addition, the simultaneous examination of alignment and branch length properties of each species' sequence compared to human (Fig.…”

Section: Resultssupporting

confidence: 73%

“…The branch lengths (as substitutions per synonymous site) between human and each species are listed (with additional pair-wise branch lengths provided in the supporting information). The last common ancestor among the catarrhine primates (A) is estimated at 25 mya (36,37), between the rodents and primates (B) at 75 mya (5,6), between eutherians and metatherians (C) at 185 mya (14), between monotremes and other therians (D) at 200 mya (14), and between mammals and birds (E) at 310 mya (13).…”

Section: Resultsmentioning

confidence: 99%

“…Within this large phylogenetic gap between eutherian mammals and birds reside the marsupials and monotremes (12,13). These metatherian and prototherian mammals diverged before the eutherian radiation, estimated at 185 and 200 million years ago (mya), respectively (14).…”

mentioning

confidence: 99%

“…These metatherian and prototherian mammals diverged before the eutherian radiation, estimated at 185 and 200 million years ago (mya), respectively (14). Indeed, these divergence dates, as well as the origins of prototherian mammals relative to metatherian mammals, remain a source of scientific debate, in part because of insufficient molecular data (13,(15)(16)(17). Until recently, very little marsupial or monotreme DNA sequence was available in public databases.…”

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confidence: 99%

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Comparative sequencing provides insights about the structure and conservation of marsupial and monotreme genomes

Margulies

Maduro²,

Thomas³

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

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Sequencing and comparative analyses of genomes from multiple vertebrates are providing insights about the genetic basis for biological diversity. To date, these efforts largely have focused on eutherian mammals, chicken, and fish. In this article, we describe the generation and study of genomic sequences from noneutherian mammals, a group of species occupying unusual phylogenetic positions. A large sequence data set (totaling >5 Mb) was generated for the same orthologous region in three marsupial (North American opossum, South American opossum, and Australian tammar wallaby) and one monotreme (platypus) genomes. These ancient mammalian genomes are characterized by unusual architectural features with respect to G ؉ C and repeat content, as well as compression relative to human. Approximately 14% and 34% of the human sequence forms alignments with the orthologous sequence from platypus and the marsupials, respectively; these numbers are distinctly lower than that observed with nonprimate eutherian mammals (45-70%). The alignable sequences between human and each marsupial species are not completely overlapping (only 80% common to all three species) nor are the platypusalignable sequences completely contained within the marsupialalignable sequences. Phylogenetic analysis of synonymous coding positions reveals that platypus has a notably long branch length, with the human-platypus substitution rate being on average 55% greater than that seen with human-marsupial pairs. Finally, analyses of the major mammalian lineages reveal distinct patterns with respect to the common presence of evolutionarily conserved vertebrate sequences. Our results confirm that genomic sequence from noneutherian mammals can contribute uniquely to unraveling the functional and evolutionary histories of the mammalian genome.comparative genomics ͉ genome sequencing ͉ genome analysis ͉ phylogenetics ͉ mammalian evolution

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Section: Resultssupporting

confidence: 73%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Comparative sequencing provides insights about the structure and conservation of marsupial and monotreme genomes

Margulies

Maduro²,

Thomas³

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

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“…Its unique mixture of mammalian, avian, and reptilian features (2) has excited biologists for more than two centuries. For geneticists, the platypus undoubtedly provides a special outgroup species because it represents the earliest offshoots of the mammalian lineage.…”

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confidence: 99%

Resolution and evolution of the duck-billed platypus karyotype with an X ₁ Y ₁ X ₂ Y ₂ X ₃ Y ₃ X ₄ Y ₄ X ₅ Y ₅ male sex chromosome constitution

Rens

Grützner

O’Brien

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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137

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The platypus (2n ‫؍‬ 52) has a complex karyotype that has been controversial over the last three decades. The presence of unpaired chromosomes and an unknown sex-determining system especially has defied attempts at conventional analysis. This article reports on the preparation of chromosome-specific probes from flow-sorted chromosomes and their application in the identification and classification of all platypus chromosomes. This work reveals that the male karyotype has 21 pairs of chromosomes and 10 unpaired chromosomes (E1-E10), which are linked by short regions of homology to form a multivalent chain in meiosis. The female karyotype differs in that five of these unpaired elements (E1, E3, E5, E7, and E9) are each present in duplicate, whereas the remaining five unpaired elements (E2, E4, E6, E8, and E10) are absent. This finding indicates that sex is determined by the alternate segregation of the chain of 10 during spermatogenesis so that equal numbers of sperm bear either one of the two groups of five elements, i.e., five X and five Y chromosomes. Chromosome painting reveals that these X and Y chromosomes contain pairing (XY shared) and differential (X-or Y-specific) segments. Y differential regions must contain male-determining genes, and X differential regions should be dosage-compensated in the female. Two models for the evolution of the sex-determining system are presented. The resolution of the longstanding debate over the platypus karyotype is an important step toward the understanding of mechanisms of sex determination, dosage compensation, and karyotype evolution.monotremes ͉ multivalent chain ͉ X-inactivation ͉ sex determination

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Evolution of X‐chromosome Inactivation

Shevchenko

Zakian

2008

Encyclopedia of Life Sciences

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X‐chromosome inactivation is a transcriptional silencing of one of the two X chromosomes that occurs in females of marsupial and eutherian mammals. The process arose and developed as a mechanism of dosage compensation during differentiation of mammalian X and Y chromosomes. X inactivation started from being imprinted and unstable in marsupials and then was transformed to random and stabile in eutherians.

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The monotreme genome: a patchwork of reptile, mammal and unique features?

Cited by 40 publications

References 86 publications

Comparative sequencing provides insights about the structure and conservation of marsupial and monotreme genomes

Comparative sequencing provides insights about the structure and conservation of marsupial and monotreme genomes

Resolution and evolution of the duck-billed platypus karyotype with an X ₁ Y ₁ X ₂ Y ₂ X ₃ Y ₃ X ₄ Y ₄ X ₅ Y ₅ male sex chromosome constitution

Evolution of X‐chromosome Inactivation

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The monotreme genome: a patchwork of reptile, mammal and unique features?

Cited by 40 publications

References 86 publications

Comparative sequencing provides insights about the structure and conservation of marsupial and monotreme genomes

Comparative sequencing provides insights about the structure and conservation of marsupial and monotreme genomes

Resolution and evolution of the duck-billed platypus karyotype with an X 1 Y 1 X 2 Y 2 X 3 Y 3 X 4 Y 4 X 5 Y 5 male sex chromosome constitution

Evolution of X‐chromosome Inactivation

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Resolution and evolution of the duck-billed platypus karyotype with an X ₁ Y ₁ X ₂ Y ₂ X ₃ Y ₃ X ₄ Y ₄ X ₅ Y ₅ male sex chromosome constitution