The Status of Dosage Compensation in the Multiple X Chromosomes of the Platypus

Janine Deakin, Timothy Hore, Edda Koina, Jennifer Marshall Graves

    Research output: Contribution to journalArticle

    60 Citations (Scopus)

    Abstract

    Dosage compensation has been thought to be a ubiquitous property of sex chromosomes that are represented differently in males and females. The expression of most X-borne genes is equalized between XX females and XY males in therian mammals (marsupials and ‘‘placentals’’) by inactivating one X chromosome in female somatic cells. However, compensation seems not to be strictly required to equalize the expression of most Z-borne genes between ZZ male and ZW female birds. Whether dosage compensation operates in the third mammal lineage, the egg-laying monotremes, is of considerable interest, since the platypus has a complex sex chromosome system in which five X and five Y chromosomes share considerable genetic homology with the chicken ZW sex chromosome pair, but not with therian XY hromosomes. The assignment of genes to four platypus X chromosomes allowed us to examine X dosage compensation in this unique species. Quantitative PCR showed a range of compensation, but SNP analysis of several X-borne genes showed that both alleles are transcribed in a heterozygous female. Transcription of 14 BACs representing 19 X-borne genes was examined by RNA-FISH in female and male fibroblasts. An autosomal control gene was expressed from both alleles in nearly all nuclei, and four pseudoautosomal BACs were usually expressed from both alleles in male as well as female nuclei, showing that their Y loci are active. However, nine X-specific BACs were usually transcribed from only one allele. This suggests that while some genes on the platypus X are not dosage compensated, other genes do show some form of compensation via stochastic transcriptional inhibition, perhaps representing an ancestral system that evolved to be more tightly controlled in placental mammals such as human and mouse.
    Original languageEnglish
    Pages (from-to)1-13
    Number of pages13
    JournalPLoS Genetics
    Volume4
    DOIs
    Publication statusPublished - 2008

    Fingerprint

    Platypus
    X Chromosome
    X chromosome
    chromosome
    gene
    dosage
    Genes
    Sex Chromosomes
    allele
    sex chromosomes
    genes
    Alleles
    alleles
    Mammals
    mammal
    mammals
    monotreme
    Marsupialia
    marsupial
    Y Chromosome

    Cite this

    Deakin, Janine ; Hore, Timothy ; Koina, Edda ; Marshall Graves, Jennifer. / The Status of Dosage Compensation in the Multiple X Chromosomes of the Platypus. In: PLoS Genetics. 2008 ; Vol. 4. pp. 1-13.
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    The Status of Dosage Compensation in the Multiple X Chromosomes of the Platypus. / Deakin, Janine; Hore, Timothy; Koina, Edda; Marshall Graves, Jennifer.

    In: PLoS Genetics, Vol. 4, 2008, p. 1-13.

    Research output: Contribution to journalArticle

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