Comparative genomic analysis of upstream miRNA regulatory motifs in Caenorhabditis

Nucleotide divergence in miRNA upstream regions and in each miRNA motif. (A) Sliding window of nucleotide divergence between C. briggsae and C. nigoni in miRNA upstream regions showing increased selective constraints in the proximity of the miRNA hairpins. The dark line indicates mean nucleotide divergence and the gray area shows the 95% confidence interval. (B) Nucleotide divergence between C. briggsae and C. nigoni for each C. briggsae motif. Motifs m1, m2, and m3 show signatures of purifying selection when compared with the random distribution. Means are represented ±1 standard error. Wilcoxon rank sum tests: (*) P < 0.05, (**) P < 0.01, (***) P < 0.001. (ns) Not significant.