A cytological and histochemical study of bone and cartilage formation in the rat

JJ Pritchard - Journal of anatomy, 1952 - ncbi.nlm.nih.gov
JJ Pritchard
Journal of anatomy, 1952ncbi.nlm.nih.gov
Recent advances in histochemical and cytological techniques have given a fresh impetus to
the study of cell morphology in relation to functional activity. So far, however, comparatively
little attention has been given to the bone-forming cells in this respect, and it was therefore
decided to investigate certain aspects of the cytology of these cells in early centres of
ossification in the hope of throwing light on the significance of the morphological changes
which accompany the differentiation of osteoblasts from their mesenchymal precursors, and …
Recent advances in histochemical and cytological techniques have given a fresh impetus to the study of cell morphology in relation to functional activity. So far, however, comparatively little attention has been given to the bone-forming cells in this respect, and it was therefore decided to investigate certain aspects of the cytology of these cells in early centres of ossification in the hope of throwing light on the significance of the morphological changes which accompany the differentiation of osteoblasts from their mesenchymal precursors, and to attempt to correlate these changes with stages in the deposition of bone matrix. Similar, but less detailed, investigations were alsocarried out on the chondroblastic series of cells. The investigation has been made on material from rat foetuses, and special attention was given to the distribution of alkaline phosphatase, glycogen, nucleo-proteins, mucopolysaccharides, mitochondria and Golgi elements. The association of alkaline phosphatase with the process of calcification in bone, cartilage and tooth has been confirmed by numerous workers since Robison (1923) first suggested it. Since Gomori (1939) published his well-known histochemical method a number of investigators have studied phosphatase activity in these tissues at the cytological level, and it is now established that osteoblasts, hypertrophic cartilage cells and odontoblasts show a high degree of enzyme activity. Variations in phosphatase activity during the differentiation of osteoblasts, and at different stages in matrix deposition, however, do not appear to have been studied, so that it is an open question whether phosphatase activity is solely, or even principally, associated with calcification, or whether it is in some way related also to the processes of cell differentiation and the deposition of the organic matrix. The presence of glycogen in calcifying tissues has long been known, but received little attention until Harris (1932) first suggested that it might be the chemical precursor of the hexosephosphate esters postulated by Robison as the substrate for alkaline phosphatase in the calcification process. The discovery by Gutman & Gutman (1941) of a phosphorylase in calcifying cartilage which could convert glycogen into hexosephosphate, and other biochemical studies of recent years, have tended to support Harris's hypothesis. Our knowledge of the precise distribution of glycogen in bone and cartilage, however, is meagre, and as in the case of alkaline phosphatase, it isnot known whether glycogen storage in these tissues is solely related to the process of calcification, or whether it has other roles. The investigations of Brachet (1947, 1950), Caspersson (1947) and others in recent years have resulted in the identification of basophilic substances in many types of cell with nucleic acids, and the hypothesis that theseare concerned in the manu-facture of proteins is strongly supported. In view of this it seemed desirable to
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