Localization of pmarg- pearlin and pmarg-aspein gene transcripts in P. margaritifera mantle tissue by in situ hybridization. Paraffin-embedded sections of oyster tissues were hybridized with antisense or sense single stranded cDNA probes labeled with digoxigenin and revealed using alkaline phosphatase-conjugated antibodies. Positive cells are stained in dark blue, sense probes showed no hybridization (data not shown). Stained cells enlargements are shown in A and B insets where scale bars are indicated. The expression partition limit is symbolized by a *. if: inner fold; mf: middle fold; of: outer fold; pg: periostracal groove; oe: outer epithelium; ie: inner epithelium; oec: outer epithelial cell.