Argyrophilic nucleolar organizer regions (AgNORs) in interphases and metaphases of normal and neoplastic gill cells of Macoma balthica (Bivalvia: Tellinidae) from the Gulf of Gdansk, Baltic Sea.

Chromosome analysis of gill cells of different populations of Macoma balthica (L.) from the Bay of Gdansk (Baltic Sea) revealed 2 clam categories, 1 with neoplastic features and 1 without. Silver-staining was performed on interphase and metaphase cells of both categories. The mean argyrophilic nucleolar organizer region (AgNOR) count per abnormal interphase cell was significantly higher than in normal interphase cells. Normal silver-stained metaphases had 3 nucleolar organizer region (NOR) chromosome phenotypes. The location of the NORs in the most frequent phenotype (55.6% in 54 metaphases scored) was interstitial on the largest metacentric chromosome pair, Pair No. 1. Abnormal silver-stained metaphases had a higher number of active NOR sites. Different phenotypes were observed (frequency greater than 10% for 67 metaphases scored); 2 were similar to those in normal metaphases and 5 were ectopic. The higher activity of AgNORs observed in abnormal cells confirmed the diagnosis of malignant neoplasia.