Chromosomal networks as mediators of epigenetic states: the maternal genome connection

Distant interactions among chromosomal loci are increasingly being seen as an important third dimension of genome biology. Thus, chromatin fibres can interact in cis and in trans to form chromatin loops and bridges, respectively. While it is generally assumed that regulatory elements from neighbouring domains or from other chromosomes interact in association to transcription or repression, this may be too simplistic. Here we propose that the evolution of genomic imprinting reflects the dissipation of epigenetic marks from a single locus, both in cis and trans, to recruit new imprinted domains. We also discuss the possibility that the genome is physically linked by means of maternal-specific epigenetic marks during development.