However, the DNA microarray only allows you to detect mRNA production, and not protein production directly, and there are examples in biology in which mRNA production and protein production are not tied together well. Some of the changes in mRNA levels may not lead to an increase or decrease in protein levels. But these changes probably represent a small fraction of the total changes observed. Our conclusions are based on a global view. Yes, a reviewer was concerned about the possibility that we were trying to compare immature mice to old mice.
Mice get sexually mature by eight weeks.
But I do not use ad libitum feeding for my control group. I decided long ago to control the calorie intake of my controls to increase our chances of studying healthy old controls. So they represent healthy aged mice. The data clearly suggest that even a modest amount of caloric restriction can have a major effect on aging, at least for muscle. Please realize that we're not measuring perhaps more informative distal end points like levels of protein carbonyls and lipid peroxides, but we're really looking at genes such as antioxidant enzymes that we think would be induced by the presence of reactive oxygen species and the like.