Overexpression of Sir2 (alias dSir2) extends lifespan by up to 57% and specifically median lifespan by 40-60%, whereas a decrease in Sir2 activity by mutation blocks the life-extending effect of caloric reduction or rpd3 mutations [15520384]. rpd3 mutants fed normal food and wild-type fed a low-calorie diet increase dSir2 expression two-fold [12459580]. Sir2 mutation does not reduce lifespan under AL. Ubiquitous Sir2 overexpression causes a 4-fold increase in Sir2 mRNA expression and an up to 57% increase in average lifespan (29% for females and 18% for males). A 10 - 20% increase in Sir2 mRNA levels causes no lifespan extension. High levels of Sir2 protein is found in nuclei of neurons and in nuclei and cytoplasm of fat body cells. Neuronal Sir2 overexpression extends average lifespan by 52% in females and 20% in males. Motor-neuronal specific expression fails to cause lifespan extension. Flies with no or with several decreased Sir2 gene function have no lifespan extension under DR. DR fails to cause further increase in lifespan or even reduces lifespan toward normal of Sir2 overexpression mutants. Mild Sir2 overexpression in the fat-body extends lifespan and reduces relative body fat content in both males and females [22661237].

Sir2 in the adult fat body regulates longevity in a diet-depending manner. A diet-dependent lifespan phenotype of Sir2 perturbations (both knockdown and overexpression) in the fat-body, but not in muscles, negates the effects of background genetic mutants. Sir2 knockdown abrogates fat-body dFoxo-dependent lifespan extension [23246004].

Decreased expression of Sir2 and Sir2-like genes in all cells causes lethality during development. Suppression of the Sir2 in neurons decreases the median lifespan by 10-30%, while ubiquitinous silinecing of the Sir2-like genes shortens lifespan. The effects are server at 28°C that at 25°C [17159295].

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