Paragonimus ohirai: identification of nucleolar organizer regions (NORs) and silver nitrate staining pattern in spermatogenesis.

The identification of nucleolus organizer regions (NORs) and the qualitative description of silver nitrate staining patterns in spermatogenesis of Paragonimus ohirai are herein reported. The NORs of P. ohirai are located on the short arm of chromosome 4 and are associated with a large amount of constitutive heterochromatin. Silver (Ag) staining was detected from the interphase stage until the prometaphase stage of mitosis in spermatogonial cells but was absent at metaphase. On the other hand, during meiosis Ag-staining of NORs occurred from prophase to the diplotene stage, then was absent from meiotic metaphase I to anaphase II and was again demonstrable in early spermatid nuclei. The appearance and disappearance of NOR during Paragonimus spermatogenesis is similar to that described for vertebrate species except during mitotic metaphase.