Presented at the Ninth Annual Meeting of the American Society for Cell Biology, Detroit, Michigan, Nov. 6-8, 1969, and Published in: J. Cell Biol. vol. 43, pp. 39a-40a (1969):

"Ultrastructural Effects of Mercuric Chloride on Nuclear Heterochromatin within Human Lymphocytes".

John H. Frenster

Department of Medicine, Stanford University School of Medicine, Palo Alto, California


Abstract:

Mercuric chloride at low concentrations (10 -5 M) induces blastic transformation, DNA synthesis, and cell mitosis when added to otherwise quiescent interphase lymphocytes (1969. J. Cell Biol. 40, 847). HgCl2 is able to bind to both nuclear proteins  (1966. Biochem. J.  98: 888) and to DNA (1961. J. Am. Chem. Soc. 83: 2599), causing a complex structural change within DNA consisting of partial strand separation, microaggregation, and a loss of hyperchromicity, all of which are fully reversible. Viable cells from the buffy coat layer of normal human blood were incubated for up to 120 hr with 10-5 M HgCl2. Cells were then fixed with glutaraldehyde, postfixed with osmium tetroxide, embedded, sectioned, stained, and examined by electron microscopy and by microspectrofluorometry. A complex reaction product was observed within the interior of the consensed heterochromatin parts of lymphocyte nuclei. The reaction product was extremely electron opaque, and consisted of tubular structures 500 A in diameter and up to 1.0 m in length, which appeared to trace the course of individual chromatin fibrils within the condensed heterochromatin masses.

Fig. 1. Human peripheral blood lymphocyte, incubated with addition of HgCl2 (10-5 M) for 24 hours. X 25,000.


Significantly less reaction product was found within heterochromatin of granulocytes and monocytes, and still less within the cytoplasm of lymphocytes, and the euchromatin part of lymphocyte nuclei was almost totally devoid of reaction product. This preferential localization of HgCl2 reaction product within the condensed heterochromatin part of lymphocytes is similar to that of  3H-phytohemagglutinin (1968. J. Cell Biol. 39: part 2, 129a), another exogenous compound which induces  blastic transformation of lymphocytes via gene de-repression. Because HgCl2 binds preferentially to single-stranded rather than to double-stranded DNA (1961. J. Am. Chem. Soc. 83: 2599), it might be expected by this means to de-repress the synthesis of RNA on such Hg-bound DNA templates (1965. Nature 208: 1093).


1. Ord MG, and Stocken LA, "Metabolic Properties of Histones from Rat Liver and Thymus Gland", Biochem. J., vol. 98: 888-897 (1966).

2. Yamane T, and Davidson N, "On the Complexing of Desoxyribonucleic Acid (DNA) by Mercuric Ion", J. Am. Chem. Soc., vol. 83, 2599-2607 (1961).

3. Pauly JL, Caron GA, and Suskind RR, "Blast Transformation of Lymphocytes from Guinea Pigs, Rats, and Rabbits induced by Mercuric Chloride in vitro", J. Cell Biol. vol. 40, 847-850 (1969).

NIH grant CA-10174


Additional References:

1. Frenster JH, "Ultrastructural Continuity Beween Active and Repressed Chromatin", Nature vol. 205: no.
4978, pp. 1341-1342 (March 27, 1965).

2. Frenster JH, "Nuclear Polyanions as De-Repressors of Synthesis of Ribonucleic Acid", Nature vol. 206: no. 4985, pp. 680-683 (May 15, 1965).

3. Frenster JH, "Electron Microscope Localization of Acridine Orange Binding within Nuclei of Human Leukemic Bone Marrow Cells", J. Cell Biol. vol. 43, p. 39a (1969).

4. Frenster JH, "Electron Microscopic Localization of Acridine Orange Binding to DNA within Human Leukemic Bone marrow Cells", Cancer Res. vol. 32, pp. 1128-1133 (August, 1971).


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euchromatin:  "the most active portion of the genome within the cell nucleus".