Influence of diet on chromatin organization in insect mid-gut cells, and its implications for the understanding of aging in this model system

Female Sarcophaga bullata were fed on three different dietary combinations: liver/water; sugar/water; and sugar/liver/water. These diets resulted in different survival patterns for the insect, with the longest lifespans being expressed on the last treatment. The Feulgen-DNA values for mid-gut cell nuclei were determined using a scanning and integrating microdensitometer. The cell nuclei of the mid-gut reacted to the presence of nutrients by an increase in the extinction values for Feulgen-DNA when compared to the unfed state. There were also significant differences between the various treatments in the extent of the activation shown by the mid-gut cells. The dietary regimes resulting in the longest lifespan showed a complete and uniform activation of the mid-gut epithelium, whereas other treatments did not. These observations suggest that changes in the chromatin organization occur with diet, and that maximum Feulgen-DNA extinctions occur (i.e. chromatin uncoiled and supporting transcription) on the sugar/liver/water diet. Nuclei showing maximum extinctions do not show an age-related change between 3 and 12 days of life. However, if the nuclear activation is partial, or incomplete, then age-related reversals in chromatin condensation take place.