To our delight, imaging with MitoRFAP-2 in the SHMT1/2 dKO cell model showed a robust decrease in the mitochondrial FA pool relative to wild-type congeners (Figure ), identifying that enzymatic serine cleavage is indeed an endogenous source of FA in mitochondria. Interestingly, MitoRFAP-2 imaging in the ADH5 KO cell line also showed depletion of mitochondrial FA relative to WT. This result is more difficult to interpret, but it suggests that mitochondria could be involved in responding to elevations in cytosolic FA fluxes by reciprocally lowering mitochondrial FA pools.