Reciprocal imprinting of human GRB10 in placental trophoblast and brain: Evolutionary conservation of reversed allelic expression

Clinical and Molecular Genetics Unit, Institute of Child Health, University College London, London WC1N 1EH, UK.
Human Molecular Genetics (Impact Factor: 6.39). 07/2009; 18(16):3066-74. DOI: 10.1093/hmg/ddp248
Source: PubMed


Genomic imprinting may have evolved not only to regulate fetal growth and development, but also behaviour. The mouse Grb10 gene provides a remarkable model to explore this idea because it shows paternal expression in brain, whereas in the placenta and most other embryonic tissues, expression is from the maternal allele. To assess the biological relevance of this reciprocal pattern of imprinting, we explored its conservation in humans. As in mice, we find the human GRB10 gene to be paternally expressed in brain. Maternal allele-specific expression is conserved only in the placental villous trophoblasts, an essential part of the placenta involved in nutrient transfer. All other fetal tissues tested showed equal expression from both alleles. These data suggest that the maternal GRB10 expression in placenta is evolutionarily important, presumably in the control of fetal growth. As in the mouse, the maternal transcripts originate from several kilobases upstream of the imprinting control region (ICR) of the domain, from a promoter region at which we find no allelic chromatin differences. The brain-specific paternal expression from the ICR shows mechanistic similarities with the mouse as well. This conserved CpG island is DNA-methylated on the maternal allele and is marked on the paternal allele by developmentally regulated bivalent chromatin, with the presence of both H3 lysine-4 and H3 lysine-27 methylation. The strong conservation of the opposite allelic expression in placenta versus brain supports the hypothesis that GRB10 imprinting evolved to mediate diverse roles in mammalian growth and behaviour.

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    • "Another gene with tissue differences in the expressed allele is GRB10, where imprinting is known to be transcript-and tissue-specific, with reported paternal expression in brain and maternal in placenta (Blagitko et al. 2000; Monk et al. 2009). We observe that muscle and blood display biallelic expression that is imbalanced towards the opposite allele than in brain, suggesting partial maternal expression, possibly driven by differences in transcript choice between tissues (Fig S16, S17). "
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    ABSTRACT: Genomic imprinting is an important regulatory mechanism that silences one of the parental copies of a gene. To systematically characterize this phenomenon, we analyze tissue-specificity of imprinting from allelic expression data in 1582 primary tissue samples from 178 individuals from the Genotype Tissue Expression (GTEx) project. We characterize imprinting in 42 genes, including both novel and previously identified genes. Tissue-specificity of imprinting is widespread, and gender-specific effects are revealed in a small number of genes in muscle with stronger imprinting in males. IGF2 shows maternal expression in the brain instead of the canonical paternal expression elsewhere. Imprinting appears to have only a subtle impact on tissue-specific expression levels, with genes lacking a systematic expression difference between tissues with imprinted and biallelic expression. In summary, our systematic characterization of imprinting in adult tissues highlights variation in imprinting between genes, individuals, and tissues. Published by Cold Spring Harbor Laboratory Press.
    Genome Research 05/2015; 25(7). DOI:10.1101/gr.192278.115 · 14.63 Impact Factor
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    • "In the mouse, Grb10 is maternally expressed from the major promoter in most tissues, whereas the brain-specific promoter is expressed from the paternally inherited allele within the diencephalon, the ventral midbrain, the medulla oblongata, and along the ventral spinal cord (Garfield et al. 2011). The human GRB10 major promoter is biallelically expressed in most tissues except in the placental villus trophoblast where it is maternally expressed, whereas the brain-specific promoter is paternally expressed in the fetal brain (Hikichi et al. 2003; Monk et al. 2009). "
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    ABSTRACT: GRB10 is an imprinted gene differently expressed from two promoters in mouse and human. Mouse Grb10 is maternally expressed from the major promoter in most tissues and paternally expressed from the brain-specific promoter within specific regions of the fetal and adult central nervous system. Human GRB10 is biallelically expressed from the major promoter in most tissues except in the placental villus trophoblast where it is maternally expressed, whereas the brain-specific promoter is paternally expressed in the fetal brain. This study characterized the ortholog of GRB10 in a marsupial, the tammar wallaby (Macropus eugenii) to investigate the origin and evolution of imprinting at this locus. The protein coding exons and predicted amino acid sequence of tammar GRB10 were highly conserved with eutherian GRB10. The putative first exon, which is located in the orthologous region to the eutherian major promoter, was found in the tammar, but no exon was found in the downstream region corresponding to the eutherian brain-specific promoter, suggesting that marsupials only have a single promoter. Tammar GRB10 was widely expressed in various tissues including the brain but was not imprinted in any of the tissues examined. Thus, it is likely that GRB10 imprinting evolved in eutherians after the eutherian-marsupial divergence approximately 160 million years ago, subsequent to the acquisition of a brain-specific promoter, which resides within the imprinting control region in eutherians.
    Molecular Biology and Evolution 07/2012; 29(12). DOI:10.1093/molbev/mss173 · 9.11 Impact Factor
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    • "Furthermore, GRB10 methylation is also correlated with expression of genes involved in reactive oxygen species (ROS) signaling, stress signaling and oxygen sensing. This is of interest because GRB10 is transcriptionally imprinted in human villous trophoblasts (and brain) and proliferation/differentiation of trophoblast cells is responsive to oxygen tension [62-64]. GRB10 has known major effects on placental growth. "
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    ABSTRACT: Infant birth weight is a complex quantitative trait associated with both neonatal and long-term health outcomes. Numerous studies have been published in which candidate genes (IGF1, IGF2, IGF2R, IGF binding proteins, PHLDA2 and PLAGL1) have been associated with birth weight, but these studies are difficult to reproduce in man and large cohort studies are needed due to the large inter individual variance in transcription levels. Also, very little of the trait variance is explained. We decided to identify additional candidates without regard for what is known about the genes. We hypothesize that DNA methylation differences between individuals can serve as markers of gene "expression potential" at growth related genes throughout development and that these differences may correlate with birth weight better than single time point measures of gene expression. We performed DNA methylation and transcript profiling on cord blood and placenta from newborns. We then used novel computational approaches to identify genes correlated with birth weight. We identified 23 genes whose methylation levels explain 70-87% of the variance in birth weight. Six of these (ANGPT4, APOE, CDK2, GRB10, OSBPL5 and REG1B) are associated with growth phenotypes in human or mouse models. Gene expression profiling explained a much smaller fraction of variance in birth weight than did DNA methylation. We further show that two genes, the transcriptional repressor MSX1 and the growth factor receptor adaptor protein GRB10, are correlated with transcriptional control of at least seven genes reported to be involved in fetal or placental growth, suggesting that we have identified important networks in growth control. GRB10 methylation is also correlated with genes involved in reactive oxygen species signaling, stress signaling and oxygen sensing and more recent data implicate GRB10 in insulin signaling. Single time point measurements of gene expression may reflect many factors unrelated to birth weight, while inter-individual differences in DNA methylation may represent a "molecular fossil record" of differences in birth weight-related gene expression. Finding these "unexpected" pathways may tell us something about the long-term association between low birth weight and adult disease, as well as which genes may be susceptible to environmental effects. These findings increase our understanding of the molecular mechanisms involved in human development and disease progression.
    BMC Medical Genomics 04/2012; 5(1):10. DOI:10.1186/1755-8794-5-10 · 2.87 Impact Factor
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