Comportamento dell'acido desossiribonucleico e dell'istone nel nucleo delle cellule ossee

Abstract

1. A quantitative investigation of both DNA and histone has been performed in nuclei of the cells directly or indirectly involved in the ossification process, i.e. preosteoblasts, osteoblasts, osteocytes, as well as periosteal fibroblasts. 2. The histophotometric technique was applied on sections of cranial vaults of newborn rats. The sections were stained according to the Feulgen method for the DNA and the “fast green” method for the histone. 3. Preosteoblasts, osteoblasts and periosteal fibroblasts are characterized by a diploid content of DNA. The preosteoblasts only reveal some tetraploid nuclei according to their mitotic activity. These findings suggest that in spite of their different functional activity the three types of cells have the same content of DNA. 4. On the contrary the DNA content of the osteocyte nucleus only amounts to 87% as regards to that of the osteoblast nucleus. The exact meaning of such a finding is at present not easily interpretable. One might speculate that it is depending upon the peculiar biological reduced activity of the osteocyte. 5. Preosteoblasts and periosteal fibroblasts show the same nuclear affinity for the “fast green”. Consequently the DNA/histone ratio in the two cell types remains unchanged. On the contrary the nuclear affinity for the “fast green” increases in the osteoblast and decreases in the osteocyte. Probably the finding concerning the osteoblast is not to be considered as a true increase in histone content but as the result of the release by the trichloroacetic acid of some radicals previously linked to the RNA, the amount of which in the nucleus of this cell is considered quantitatively high. On the other hand the finding concerning the osteocyte might be considered the result either of a true decrease in the histone content or of a decreased release of radicals depending upon a seemingly lower content of RNA.