DNA methylation of Kr-h1 is involved in regulating ovary activation in worker honeybees (Apis mellifera)

Abstract

A fundamental feature of insect colonies is the presence of a sterile worker caste. In the presence of a queen, worker reproduction is suppressed, leading to degradation of the ovaries. However in the absence of the queen, some young workers activate their ovaries and lay eggs that can result in viable male offspring. The genetic and molecular mechanisms that underlie the regulation of worker sterility are only partially understood, but are of great interest since they are fundamental to the evolution of eusociality. Here, we determine whether DNA methylation of the transcription factor, Kruppel homolog 1 (Kr-h1), is associated with ovary activation in workers of honeybee. Workers were reared under queenless conditions and separated into control and CO2-treated cages (CO2 narcosis is known to suppress ovary activation in queenless workers). Patterns of DNA methylation of Kr-h1 in the ovaries of 7-day-old adult workers showed that non-active ovaries had significantly higher levels of methylation at 4 CpG sites compared to workers with active ovaries. CO2 narcosis inhibited ovary activation, but did not alter methylation levels in non-active ovaries. These findings suggest that methylation of Kr-h1 contributes to the regulation of worker sterility in the honeybee. In addition to the overall finding of differential methylation between ovary-activated and non-activated workers, we found evidence of allele-specific methylation at one site.