[Incorporation of H3-uridine in vitro into normal lymphocytes and those in cases of aberration of acrocentric chromosomes]

Abstract

Literature data indicate that the formation of ribosomes is a basic function of the nucleolus. The formation of the nucleolus depends upon the function of the nucleolus organizing region (NOR). It was shown that in man the NOR locus is situated in secondary constrictions and adjacent segments of the short arms of acrocentric chromosomes of the D and G group. The presence of DNA sequences coding for 18 S and 28 S RNA i.e. ribosomal RNA (r-RNA), was demonstrated in the secondary constriction of acrocentric chromosomes using the RNA-DNA hybridization in situ method. The genes coding for 5 S RNA which is also a component of ribosomes, are located on other chromosomes. Therefore ribosome production should be considered a polygenic process, the genes situated in the NOR locus playing a basic role in its initiation. In cases of acrocentric chromosome aberration NOR "dosage" changes; in cases of regular trisomy there are 11 NOR "doses" instead of the normal 10, occurring in 5 pairs of group D and G chromosomes, in cases of translocation trisomy there are 9 such "doses" and in cases of balanced translocation carriers there are 8 "doses". Hence the following question: do changes in the NOR "dose" cause changes in ribosome production? Eventual changes should influence the intensity and/or the time course of r-RNA synthesis in cells stimulated to growth and differentiation . An approximate index for the study of this phenomenon is the 3H-uridine incorporation in an adequate experimental system. It seems that the most convenient model to study this phenomenon is the blastic transformation of lymphocytes induced by phytohaemagglutinin. This process has already been investigated in depth and is well known, the material being easily accessible. Venous blood was taken from 10 patients with 21 regular trisomy, 2 cases of 21 translocation trisomy and from 21 carriers of balanced translocations. Lymphocytes from 12 healthy persons with a normal karyotype served as controls. Lymphocytes in plasma were separated from whole blood and a routine macroculture was set up adding phaseoline of standardized mitogenic activity in the quantity 0.02 ml/ml of medium. The cells were incubated for 3, 6, 12, 24 and 48 hours. One hour before termination of the incubation period 1 microCi/ml 3H-uridine was added to the medium.(ABSTRACT TRUNCATED AT 400 WORDS)