How Imprinted Genes Shape Nurturing Behaviours and Neural Circuits.

Background: Genomic imprinting is an epigenetic phenomenon that, in animals, is found only in viviparous mammals, such as eutherians and marsupials. Differential epigenetic marking of the genomes during gametogenesis leads to parent-of-origin-specific expression of imprinted genes, with some solely expressed from the maternally inherited allele, and others solely expressed from the paternally inherited allele. From an evolutionary perspective, genomic imprinting is fascinating, as it appears to negate the benefits of diploidy and yet correct expression of imprinted genes essential for normal development and function.

Summary: Genomic imprinting influences some key mammalian physiologies, including brain and behaviour. Imprinted gene expression is enriched in the "parental hub" neurons of the hypothalamus and the wider defined parental care circuitry. Furthermore, manipulation of a number of these imprinted genes in mice leads to changes in parental care giving.

Key messages: We propose that imprinted genes are likely to influence parental behaviour at several levels. Given their over-representation, it is probable that the recognised "imprinted gene network" operates within the parental hub neurons of hypothalamus. In addition, expression of imprinted genes in the wider brain circuitry, and the pituitary, may modulate different aspects of parental care behaviour. Finally, the known functional consequences of altered imprinted gene expression most likely arise due to changes in the development and/or cellular composition of the parental care circuitry. However, it is clear there remains much to be discovered before we fully understand how and why genomic imprinting shapes nurturing and parental behaviours.