From Exaptation to Adaptation: Stress, Transposons, and Functions of the Deep Genome

Adaptation to the environment is indispensable for organismal fitness. The brain is responsible for detection of and adaptation to stressful stimuli. Few molecular mechanisms facilitating this response have been described including neuronal plasticity, neurogenesis, and changes in gene expression. With the advent of next-generation sequencing technologies, large swathes of the noncoding genome have been identified and a role for the deep genome in governing the neural response to stress has been outlined. For instance, in the hippocampus heterochromatin remodeling is observed in gene deserts, here, marking repetitive retroelements selectively for transcriptional silencing. Aberrant retroelement expression is predicted to contribute to functional deficits in stress-sensitive brain regions. Though not yet fully realized, this “junk” represents a novel frontier in stress physiology relevant to many stress-related pathologies.