Transcription Dynamics and DNA Methylation Responses to Growth Modification.

To better understand how gene transcription is controlled under different physiological and environmental conditions, we assessed transcription and methylation responses in a vertebrate system (salmon) where growth can be manipulated in response to growth hormone transgenesis or under satiated, feed-deprived, and re-fed experimental conditions. In both transgenic and non-transgenic liver tissue, methylation of gene promoters was negatively associated with transcription at all measured times. However, the changes in promoter methylation among time-points did not generally correlate with changes in gene transcription among treatments. The results from this study suggest that only a subset of genes are readily responsive to changes in promoter methylation for a given environmental shift such as feed-deprivation or a physiological shift such as growth hormone transgenesis (i.e., genotype-by-environment interactions). The present study also reveals the complexity of how one tissue responds to alterations in internal changes in physiology (growth modification by growth hormone transgenesis; genotype), external environmental conditions (food availability; environment), and their interactions (genotype-by-environment effects).