Compared to the growing body of literature characterizing associations between DNA methylation patterns and maternal cigarette smoking during pregnancy, much less is known about associations between maternal cigarette smoking during pregnancy and microRNA (miRNA) expression. miRNA are small, ~22 nucleotide-long noncoding RNA molecules, previously shown to be highly ubiquitous and have conservation across many species (R. C. Lee, Feinbaum, & Ambros, 1993). miRNA control gene expression by base-pairing to the 3′-untranslated region of a target messenger RNA (mRNA). In some cases, there will be an imperfect match, or imperfect complementarity, between the miRNA and its mRNA target, which results in problems translating the mRNA into a protein molecule, through a mechanism called translational repression. In other cases of perfect complementarity between the miRNA and the target mRNA, the result is degradation of the target mRNA. Research has found that since partial or imperfect complementarity of a miRNA to a target mRNA can still result in translational repression, a single miRNA has the capability of regulating a number of genes (Du & Zamore, 2007). Through this mechanism of negative regulation, miRNA
