Transgenerational inheritance of gene silencing: a model of biological memory

A distinctive feature of living systems is their ability to record and maintain memories over long timescales. To understand how the functional properties of memory systems can be established by biological circuits, we focus on the transgenerational inheritance of gene silencing in C elegans worms. In response to a trigger, worms silence a target gene for multiple generations, resisting dilution due to growth and reproduction. Silencing may also be maintained indefinitely upon selection. We show that the hallmark properties of the system can be explained by a minimal model of biological memory in which competition for silencing machinery leads to self-organization around a critical state near the transition to bistability. We show that this mechanism is robust to noise and static variation, and offers insights into the design principles of other long-term memory systems.