Concepts of function of peripheral non-chromatin and endosome in Entamoeba histolytica

The distribution of RNA (to a lesser extent DNA) in the nucleus of E. histolytica appeared to be the opposite of what one found in other eukaryotic cells (originally stated by Pan and Geiman in 1955). Autoradiographs of amebae labelled with 3H-thymidine revealed primarily randomly distributed DNA-3H (probably euchromatin) in interphase cells. This DNA was so low in amount in individual cells that it usually did not stain with the Feulgen procedure. A small amount of DNA-3H was also detected by autoradiography in the peripheral chromatin (= rDNA?; occasionally it was abundant) and endosome. Clumps of DNA-3H were also observed around the endosomal area in some amebae. This labelling pattern was not observed in 3H-uridine (for RNA) incorporation experiments. These data were consistent with the possibility that the endosome, which was sometimes Feulgen +, was a site of condensation of DNA prior to nuclear division. As detected by light and electron microscopy autoradiographic analysis of 3H-uridine incorporation, RNA was synthesized (or accumulated) primarily in the peripheral chromatin; lesser amounts were evenly distributed. Most of the peripherally located amebal nuclear RNA was probably rRNA and/or precursor rRNA. If this is the case, it is probable that the peripheral chromatin, although structurally unlike nucleoli, may be "functionally" comparable to nucleoli of eukaryotes.