Nonrandom distribution of metaphase AgNOR staining patterns on human acrocentric chromosomes

The metaphase nucleolar organizer regions (NORs) contain ribosomal genes as sociated with proteins such as upstream binding factor (UBF) and RNA polyme rase I (RPI). These genes are clustered in 10 loci of the human acrocentric chromosomes (13, 14, 15, 21, and 22). Some NOR-associated proteins, termed AgNOR proteins, can be specifically stained by silver. In this study we to ok advantage of technical advances in digital imaging, image restoration te chniques, and factorial correspondence analysis (FCA) to study the differen t AgNOR staining patterns of metaphase chromosomes in human lymphocytes. Th ree predominant patterns could be distinguished: pair (47%), slick-like (28 %), and unstained (18%) structures. By studying the frequency of occurrence of each pattern on different chromosomes, two groups could be defined. Chr omosomes 13, 14, and 21 carried predominantly pair or stick-like AgNOR stru ctures, whereas chromosomes 15 and 22 mainly carried pair AgNOR structures or remained unstained. We suggest that the different AgNOR shapes reflect b oth the number of ribosomal genes carried by each chromosome and the differ ential recruitment of active ribosomal genes in each NOR cluster. This is t he first study showing a nonrandom distribution of AgNOR shape among acroce ntric chromosomes.