mRNA is Synthesized Mainly at the Phase between the Euchromatin and Heterochromatin: Proposal of a Phase Theory

ABSTRACT

BACKGROUND: Malignant cell nuclei, in general, have increased amounts of heterochromatin and decreased electron densities of euchromatin, making the chromatin pattern coarser than that of benign cell nuclei. The chromatin pattern in benign and malignant cells, however, is barely explained in terms of molecular structure. In this study, the chromatin pattern of metaplastic and carcinomatous squamous cells of the uterine cervix was correlated with transcriptional activity by ultrastructural autoradiography. METHODS: Punch-biopsied tissues were cultured with 3H-uridine for 5 minutes and processed for electron microscopy. Thin sections of the tissues on nickel grids were covered with photosensitive emulsion and kept cold in a dark room for 10 to 16 weeks. After development and staining, the tissues were observed by electron microscopy. RESULTS: The nuclei of the metaplastic squamous cells consisted mostly of euchromatin. A few silver grains were observed, mainly at the periphery of the nuclei. The nuclei of the carcinomatous cells had increased amounts of heterochromatin along the nuclear membrane, and also in the euchromatin area. Silver grains were observed mainly at the boundary between the heterochromatin and euchromatin. CONCLUSION: These findings suggest that an increased amount of heterochromatin in carcinomatous cells results in an increase of the boundary area between the heterochromatin and euchromatin, an area which may be a transcriptionally active site.