Biased Expression of Parental Alleles in the Human Placenta

Abstract

The biased expression of parental alleles plays a fundamental role in the formation of the placenta as a multifunctional organ necessary for the development and survival of the fetus. First of all, this is expressed in the phenomenon of imprinting, when only the maternal or paternal allele is expressed in placental cells. The placenta uses an extended range of imprinting mechanisms compared to the embryo – histone modifications that suppress or, conversely, activate the expression of nearby genes, regulatory sequences and genes derived from retroviruses or retrotransposons, microRNAs that function as antisense RNAs and participate in transcriptional and post-transcriptional regulation of gene expression. In addition, incomplete suppression of the activity of one of the parental alleles is detected in the placenta, leading to a biased imprinted expression of some genes. This review shows the role of biased expression of parental alleles in the development of placental structures of an embryo, discusses the mechanisms of epigenetic control of parental alleles, mainly expressed in the placenta.