Identifying the epigenetic determinants of gene-by-environment interactions using Drosophila melanogaster diapause as a model
Authors: Abigail DiVito Evans; Paul Schmidt; Mia Levine
Affiliation: University of Pennsylvania, Philadelphia, PA
Keywords: o. genotype-by-environment interaction; j. epigenetics
Genes and the environment interact to pace developmental transitions. The initiation, cessation, and pausing of such transitions typically depend on genotype-specific responses to environmental cues, i.e. gene-by-environment interactions (GxE). Here we investigate the epigenetic determinants of GxE in the context of developmental pausing. We exploit a seasonally- and geographically- variable reproductive arrest phenotype (“diapause”) in Drosophila melanogaster. Diapausing females suspend reproduction in response to low temperatures and short days that signal the start of winter. When warm temperatures and long days return in the spring, the arrested ovaries re-initiate egg development. This arrest is accompanied by extensive and coordinated changes in gene expression in the ovary. We hypothesize that epigenetic factors control the diapause gene expression program in the ovary and that this epigenetic control depends on genotype. Consistent with epigenetic regulation, inbred lines that lack genetic variation exhibit incomplete penetrance—only a portion of individuals in the same environment with the same genetic background enter diapause. To identify epigenetic factors that mediate gene expression GxE in diapause, we exploit genetic variation between inbred lines with differing diapause penetrance (a “high penetrance” line with 90% diapause and a “low penetrance” line with 5% diapause). Using Western Blots, we screened histone mark abundance of H3K36me1, H3K27me3, H3K9me3, and H3K4me3 between diapause and age- and temperature- matched reproductive ovaries. We discovered that H3K4me3 is depleted in diapause ovaries, but only in the high penetrance line. We predict that experimentally depleting H3K4me3 in the ovary of the high penetrance line will increase diapause penetrance while experimentally elevating H3K4me3 will decrease diapause penetrance. We predict no such effects in the low penetrance line. We will present the consequences of H3K4me3-depletion and -enrichment in both lines and determine whether H3K4me3-dependent penetrance is genotype-specific. Analyzing RNA-seq reads from these same ovaries, we will delineate those H3K4me3-sensitive genes and pathways that are also differentially regulated by the diapause gene expression program. Together, these data may reveal genotype-dependent epigenetic regulation of GxE that mediate an important adaptive phenotype.