Expression levels of dpp transcripts in adult mantle edge tissue. Comparison of the levels of dpp transcripts between the left and right sides of the mantle tissue by quantitative reverse transcription (RT)-PCR analysis using EF-1α transcripts as reference. In the non-coiled shelled limpets, Patella vulgata and Nipponacmea fuscoviridis, dpp expression levels were not different between left and right sides of mantle tissues. By contrast, in the coiled-shell snail Lymnaea stagnalis (dextral and sinistral), dpp expression levels were significantly different (asymmetric) (Wilcoxon–Mann–Whitney test; P<0.05). Gene expression levels were standardized by dividing the values by those of the left side (P. vulgate, N. fuscoviridis, and the dextral strain of L. stagnalis), or by those of the right side (sinistral strain of L. stagnalis). Error bars represent standard deviations.