The genome is partitioned into topologically associated domains and genomic 
compartments with shared chromatin valence. This architecture is constrained by 
the DNA polymer, which precludes interactions between genes on different 
chromosomes. Here we report a marked divergence from this pattern of nuclear 
organization that occurs in mouse olfactory sensory neurons. Chromatin 
conformation capture using in situ Hi-C on fluorescence-activated cell-sorted 
olfactory sensory neurons and their progenitors shows that olfactory receptor 
gene clusters from 18 chromosomes make specific and robust interchromosomal 
contacts that increase with differentiation of the cells. These contacts are 
orchestrated by intergenic olfactory receptor enhancers, the 'Greek islands', 
which first contribute to the formation of olfactory receptor compartments and 
then form a multi-chromosomal super-enhancer that associates with the single 
active olfactory receptor gene. The Greek-island-bound transcription factor LHX2 
and adaptor protein LDB1 regulate the assembly and maintenance of olfactory 
receptor compartments, Greek island hubs and olfactory receptor transcription, 
providing mechanistic insights into and functional support for the role of trans 
interactions in gene expression.