In order to elucidate mechanisms of aging, downstream effects of experimental manipulations that extend lifespan need to be fully characterized. For example, identification of a gene for a mutation that extends lifespan does not by itself explain how the gene achieves this. Here, physiological, biochemical, and cell biological studies become essential.
Biochemical and cell biological approaches in Drosophila are well developed and easy to utilize. A large number of protocols for procedures such as DNA and RNA extractions and purification of mitochondrial DNA can be found in the literature (see Recommended Resources section).
Usually most types of measurements that have been performed in other model species such as rodents can also be applied to Drosophila. Preparation of tissue homogenate is easy, and potential aging biomarkers such as protein, lipid and DNA oxidative damage can be measured, as well as various metabolites and enzyme activities. Mitochondria are easily prepared from the homogenates (Miwa et al., 2003), and respiration rate, reactive oxygen species production, membrane potentials and mitochondrial enzyme activities can be measured.
Physiological measures are important because they can provide insight into the nature of aging processes, which may not be apparent from the "age-at-death" measure that is used in demographic studies. A number of different types of behavioral assays such as learning and memory have been established (Connolly and Tully, 1998). Also there are other measures that are relevant to aging; number of eggs laid, negative geotaxis, immune function (DeVeale et al., 2004), heart function (Wessells et al., 2004), and circadian rhythm (Driver, 2000). Metabolic rate can be assayed by respirometry/ calorimetry (Hulbert et al., 2004), and stress resistance can be tested in various forms, including hydrogen peroxide, paraquat feeding, cold, starvation, and desiccation.
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