Adaptation

Adaptation occurs when a stimulus that once elicited a particular response, now elicits the opposite reaction. In C. elegans, this behavior has been shown through chemotaxis studies where extended exposure to an odor in the absence of food will result in a suppression of the chemotaxis response. In addition, by coupling an attractive stimulus to a starvation environment, the once attractive chemical is responded to as a repellent. However, these adaptations can be restored by brief exposure to the stimulus in the presence of food.

Unfolded protein response

The unfolded protein response (UPR) is a stress response that is critical to maintaining protein homeostasis (proteostasis)- the functional concentration of properly folded protein concentration in an organism. The UPR in entirety involves stress signals in the endoplasmic reticulum the mitochondria and the cytoplasm that are activated by increases in misfolded proteins. The increase in misfolded proteins affect protein concentration and can result in the aggregation of protein species. To restore protein homeostasis, these stress signals up-regulate or down-regulate protein transcription as well as regulate protein translation. These systems also influence protein folding by increasing the concentration of chaperones to aid in the folding process. In addition, these systems can increase the activity of the endoplasmic reticulum-associated degradation (ERAD) pathway, to deal with the increase in misfolded proteins. Eventually, sustained activation of the UPR will lead to cellular apoptosis.