Electron microscopic observations on the development and cytochemistry of the large granule complexes in chicken...

Large granule complexes are structures found in a small percentage of chicken erythrocyte nuclei when observed in ultra-thin sections in the electron microscope. They consist of an amorphous region associated with a number of large (approximately 30 min) granules. We have shown, by a novel use of phenylhydrazine to synchronize populations of chicken erythrocytes in vivo, that large granule complexes do not occur in the nuclei until the cells have reached one-third to one-half of their normal intravascular lifespan. The mature large granule complexes are formed by aggregation of pre-existing fibrillar, granular and amorphous material, and their presence is correlated with the presence of another ultrastructural feature of the nucleus, the so-called "filled cavities' in the chromatin. Digestion of ultra-thin sections of erythrocytes embedded in the hydrophilic resin glycol methacrylate (GMA) has shown that the major component of the amorphous region is a rather acidic protein that is not haemoglobin, the most abundant protein in the erythrocyte. The large granules also contain protein and, almost certainly, RNA. The problems encountered in reaching this conclusion have emphasized the lack of unambiguous cytochemical tests for use on ultra-thin sections. We have shown that the large granule complex differs in many respects from the nucleolus in the erythrocyte series, even though the two organelles have certain superficial similarities such as their overall dimensions and the presence of granular and fibrillar regions. The most likely function of the large granule complex is as a repository for material, including RNA, the processing of which has ceased in the inactivated erythrocyte nucleus.