Figure 5.

Intermittent Repeat Expansions Can Lead to Conserved, Lineage-Specific, and Species-Specific CTCF Binding in Mammals

A CTCF-binding site found within an ancient transposon shows conserved binding in placental and nonplacental mammals (left data inset) and must have been present in the mammalian ancestor (ur-Mammal). In contrast, a CTCF-binding site generated in the eutherian ancestor (ur-Placental) shows conserved binding across placental mammals but is absent in marsupials (right data inset). More recent CTCF-binding expansions lead to increasingly lineage- and species-specific CTCF binding. For example, the expansions of B2 repeats in the mouse and rat ancestor (ur-Rodent) created CTCF binding that is highly shared between mouse and rat, whereas the continued B2 expansions along both lineages also generated species-specific CTCF-binding sites (see Figure 4C). See also Table S3.