Monoallelic gene expression and mammalian evolution

Abstract

Monoallelic gene expression has played a significant role in the evolution of mammals enabling the expansion of a vast repertoire of olfactory receptor types and providing increased sensitivity and diversity. Monoallelic expression of immune receptor genes has also increased diversity for antigen recognition, while the same mechanism that marks a single allele for preferential rearrangement also provides a distinguishing feature for directing hypermutations. Random monoallelic expression of the X chromosome is necessary to balance gene dosage across sexes. In marsupials only the maternal X chromosome is expressed, while in eutherian mammals the paternal X genes are silenced in the developing placenta and early blastocyst. These examples of epigenetic gene regulation commonly employ asynchrony of replication, the binding of polycomb proteins and antisense RNA, and histone modifications to chromatin structure. The same is true for genomic imprinting which among vertebrates is unique to mammals and represents a special kind of epigenetic modification that is heritable according to parent of origin. Genomic imprinting pervades many aspects of mammalian growth and evolution but in particular has played a significant role in the co-adaptive evolution of the mother and foetus.

Coadaptation and conflict, misconception and muddle, in the evolution of genomic imprinting

“…In recent years, mother-offspring coadaptation has gained popularity as an explanation of the evolution of genomic imprinting that does not invoke evolutionary conflict and is considered by some to fit the empirical data better than the parental conflict hypothesis (Bourc'his and Proudhon, 2008). This coadaptation hypothesis is sometimes presented as an amalgam of the verbal arguments of Keverne and colleagues (Curley et al, 2004;Swaney et al, 2007;Keverne and Curley, 2008;Keverne, 2009) and an explicit model of Wolf and Hager (2006). What the former have to do with the latter is obscure, apart from use of the common term 'coadaptation,' and this paper will consider them separately.…”

Semele: A Killer-Male, Rescue-Female System for Suppression and Replacement of Insect Disease Vector Populations

“…Such a cellular counting system has not yet been engineered by humans; but it is a task that has been achieved by nature, in the context of sex determination in Drosophila (Sanchez 2008) and during X chromosome inactivation and allelic exclusion in mammals (Keverne 2009;Zakharova et al 2009). One possible method for achieving this takes advantage of pairing-sensitive silencing, a phenomenon in which the presence of specific sequences near genes located at the same site on homologous chromosomes results in strong silencing of these genes in homozygotes, but much weaker silencing in heterozygotes (Kassis 2002).…”

Behavioural Genetics in the Postgenomics Era

“…Mice null for the maternally imprinted/paternally expressed genes, Peg1 and Peg3, both of which are strongly expressed in the brain, exhibit a reduction in oxytocin neurons and reductions in quality of maternal care (Champagne et al, 2009). When Peg3 transcription is inactivated in the hypothalamus of the pregnant mother carrying wild-type offspring, the functional phenotypic outcomes are very similar to those that occur when the same gene is inactivated selectively in the developing placenta and fetal hypothalamus in a wildtype mother (Keverne, 2009).…”