Differentiation of the guinea pig eye: Nuclear ultrastructure,template activity and DNA content

Summary Nuclei of various cell types in the eye of embryonal and adult Guinea pigs were studied by means of electron microscopy, cytophotometry and autoradiography. Striking differences in condensation and arrangement of chromatin were found between the different tissues and cells. Several nuclear types were analyzed quantitatively with regard to their content of condensed and decondensed chromatin by means of electron microscopic morphometry. Structural differences in chromatin organization coincided with different nuclear DNA contents in various cell types of the retina, such as bipolar cells, Müller cells, rods and cones, and the pigmented epithelium.The differences between DNA-Feulgen means obtained by cytophotometric analysis were highly significant. Template activity as shown by³H-uridine incorporation made evident that the rate of RNA synthesis is positively correlated with the quantity of decondensed chromatin. It is speculated that differentiation of the Guinea pig eye involves differential DNA synthesis, and that the extra-DNA could have some trigger function for the pattern of chromatin condensation and thus the pattern of gene expression.