The implications of satellite DNA instability on cellular function and evolution

Abundant tandemly repeated satellite DNA is present in most eukaryotic genomes. Previous limitations including a pervasive view that it was uninteresting junk DNA, combined with challenges in studying it, are starting to dissolve - and recent studies have found important functions for satellite DNAs. The observed rapid evolution and implied instability of satellite DNA now has important significance for their functions and maintenance within the genome. In this review, we discuss the processes that lead to satellite DNA copy number instability, and the importance of mechanisms to manage the potential negative effects of instability. Satellite DNA is vulnerable to challenges during replication and repair, since it forms difficult-to-process secondary structures and its homology within tandem arrays can result in various types of recombination. Satellite DNA instability may be managed by DNA or chromatin-binding proteins ensuring proper nuclear localization and repair, or by proteins that process aberrant structures that satellite DNAs tend to form. We also discuss the pattern of satellite DNA mutations from recent mutation accumulation (MA) studies that have tracked changes in satellite DNA for up to 1000 generations with minimal selection. Finally, we highlight examples of satellite evolution from studies that have characterized satellites across millions of years of Drosophila fruit fly evolution, and discuss possible ways that selection might act on the satellite DNA composition.