The Evolution of the DLK1-DIO3 Imprinted Domain in Mammals
Figure 7
Evolution of the Dlk1-Dio3 Domain in Mammals.
Schematic illustration of the evolution of the Dlk1-Dio3 domain in mammals. RTL1 retrotransposed into the region before the divergence of the eutherians and metatherians. In the marsupial lineage, RTL1 did not gain a function (or lose it) and became degraded. The region expanded approximately 2-fold in the marsupials; this expansion is mainly due to the accumulation of LINE1 repeats. The snoRNA and miRNA clusters arose after eutherian diverged from marsupials but before the mammalian radiation which took place around 98 million years ago. The eutherian region has also evolved many genomic features associated with imprinted clusters. The entire domain has become increasingly GC-rich, whereas a decline in GC content is the general trend in eutherian genomes. There are fewer SINEs than expected in the region, and the introns of the DLK1 transcript have become shorter. Finally the region has a sub-telomeric position within the eutherian genome whereas in monotremes and marsupials it is in the middle of the chromosome arm. Not drawn to scale