MicroRNAs are likely part of the molecular toolkit regulating adult reproductive diapause in the mosquito, Culex pipiens

For many arthropods, including insects, diapause is the primary mechanism for survival during unfavorable seasons. Although the exogenous signals and endogenous hormones that induce and regulate diapause are well-characterized, we still lack a mechanistic understanding of how environmental information is translated into molecular regulators of the diapause pathway. However, short, non-coding microRNAs (miRNAs) are likely involved in generating both the arrested egg follicle development and fat hypertrophy in diapausing females of the Northern house mosquito, Culex pipiens. To determine whether miRNAs might respond to changes in day length and/or regulate diapause pathways, we measured the abundance of candidate miRNAs in diapausing and nondiapausing females of Cx. pipiens across the adult lifespan. Of the selected miRNAs nearly all were more abundant in nondiapausing females relative to diapausing females, but at different times. Specifically, miR-13b-3p, miR-14-3p, miR-277-3p, and miR-305-5p were upregulated in nondiapausing females early in adulthood, while miR-309-3p and miR-375-3p were upregulated later in adult life, and miR-8-3p and miR-275-3p were upregulated both early and late in adult life. Taken together, our data demonstrate that miRNA expression is dynamic, changing across adult lifespan. Further, differential miRNA expression between diapausing and nondiapausing females of Cx. pipiens suggests that this epigenetic mechanism is part of the molecular toolkit regulating diapause.