Prognostic significance of AgNOR Proliferative Index in gallbladder carcinoma - A potential alternative to frozen section analysis

The Nucleolar Organizer Regions (NORs) were first described by Heitz (1931) and McClintock (1934) as weakly stained chromatin regions around which, at the end of telophase, nucleoli are reformed after their disappearance during the mitotic phase of the cell cycle. NORs, located on short arm of acrocentric chromrsomes (Chromosome number 13,14,15,21 and 22) contain ribosomal genes which encode for ribosomal RNA and play an important role in protein synthesis [1,2]. NORs are considered to be a marker of both DNA transcriptional activity and DNA transcriptional potential [3]. Associated with these regions are certain acidic and argyrophilic, non-histonic proteins called NOR-Associated Proteins (NORAPs). NORs can be demonstrated in tissue sections by staining their associated proteins with colloidal silver and these reaction products represent the Argyrophilic Nucleolar Organizer Regions (AgNORs) which appear as black dots of various sizes in the nucleolus and nucleus [4].