In organisms distantly related, regulation of gene expression involves the same epigenetic mechanisms acting on different biological processes. Molecular analysis of genomic imprinting, an epigenetic phenomenon observed in plant and animal species, highlights that not only this epigenetic mechanism but also their response pathways are functionally conserved, allowing, therefore, inter-kingdom comparisons.
In the study of the epigenetic mechanisms of gene regulation, genomic imprinting is probably the most interesting one. Genomic imprinting is a critical epigenetic process brought about through the allelic-specific epigenetic modification leading to the parent-of-origin specific gene expression (Cui 2007). Examination of genomic imprinting in organisms as diverse as mammals, insects, and plants suggests that it is accomplished through phylogenetically conserved mechanisms. Histone modifications are a common signature in genomic imprinting and these epigenetic marks are utilized in order to establish higher-order chromatin structures that contribute to the imprinting of whole chromosomes, single genes, or gene clusters (McEachern 2010, McEachern 2012). Plants and mammals utilize a homologous Polycomb complex, the Polycomb Repressive Complex 2 (PRC2), to catalyze repressive histone methylation at silenced imprinted alleles. Regulation of genomic imprinting in the plant Type I MADS-box gene pheres1 (phe1) from Arabidopsis requires histone methylation introduced by the activity of PRC2, in addition to methylation at repetitive DNA sequences by DECREASE IN DNA METHYLATION1 (DDM1), which belongs to the SWI/SNF protein remodeling complex (Schmidt et al. 2013). In animals, PRC2 contributes to chromatin compaction, by catalyzing the methylation of histone H3 at lysine 27, thus playing a key role in various biological processes such as differentiation and stem-cell plasticity (Margueron and Reinberg 2011).
- Cui H. 2007. Loss of imprinting of IGF2 as an epigenetic marker for the risk of human cancer. Dis Markers. 23:105-112.
- Margueron R, Reinberg D. 2011. The Polycomb complex PRC2 and its mark in life. Nature 469:343-349.
- McEachern LA. 2010. Inter-kingdom epigenetics: characterization of maize b1 tandem repeat-mediated silencing in Drosophila melanogaster. PhD dissertation. Dalhousie University (Canada).
- McEachern LA. 2012. Transgenic epigenetics: using transgenic organisms to examine epigenetic phenomena. Genetics research international. doi:10.1155/2012/689819.
- Schmidt A, et al. 2013. The Polycomb group protein MEDEA and the DNA methyltransferase MET1 interact to repress autonomous endosperm development in Arabidopsis. Plant J. 73:776-787.