In our proposed model the levels of ER stress (UPR) are basal during regeneration in feeding conditions at 72hR and not essential for stem cell proliferation and regeneration. Planarians obtain energy and lipids from administered food, including exogenous fatty acids (exo FA). During starved conditions, ccts increase the levels of the UPR and this allows proper stem cell proliferation and regeneration when exogenous fatty acids are not available. 