Potential Difference Across the Nuclear Membrane: A Regulator of Gene Expression?

Detection of a large cation-selective channel in nuclear envelopes of avian erythrocytes

To determine whether the nuclear envelope of eukaryotic cells has the capability to regulate ion fluxes, we have used the patch-clamp technique to detect ion channels in this membrane system. Since possible sites for ion channels in the nuclear envelope include not only the nuclear pores, but also both the inner and outer nuclear membranes, we have patched giant liposomes composed of phosphatidylcholine and nuclear envelope fragments isolated from mature avian erythrocytes. A large, cation-selective channel with a maximum conductance of approximately 800 pS in symmetrical 100 mM KCl was detected. This channel is a possible candidate for a nuclear pore.

A 41-42 bp tandemly repeated sequence isolated from nuclear envelopes of chicken erythrocytes is located predominantly on microchromosomes

To study whether specific DNA sequences are associated with nuclear membranes, residual DNA was extracted from DNase-treated nuclear envelopes prepared from erythrocytes of adult chickens (Gallus domesticus). This DNA was then blunt-end ligated into a bacterial plasmid vector. DNA blot analysis and nucleotide sequence determination revealed that approximately 30% of the cloned fragments consisted of different multiples of a 41-42 bp tandemly repeated, partially symmetrical sequence. In situ hybridization to chicken chromosomes demonstrated that the sequence was located primarily on microchromosomes, although some hybridization was also observed to macrochromosomes 7 and 8. Digestion of chicken DNA with any of a number of restriction enzymes did not completely reduce the intensity of a high molecular weight band to which the repeated sequence hybridized. These results, along with those obtained from in situ hybridization, suggested that many copies of this sequence are organized into large tandem arrays, and are not dispersed in many shorter repetitive blocks throughout the chicken genome. Although the repetitive sequence constituted approximately 10% of the chicken genome, it did not hybridize to quail or turkey DNA.

Exposure of human cells to low-frequency electromagnetic fields results in quantitative changes in transcripts

The exposure of human cultured cells to electromagnetic signals with extremely low repetition rates resulted in an increased level of selected RNA transcripts. RNA with homology to beta-actin, histone H2B, and v-myc DNA was monitored by dot blot hybridization following 20 min exposures of HL60 cells to five different electromagnetic signals. The experiments used three asymmetric electromagnetic signals with different repetition rates, and two symmetric sinusoidal signals, delivered at 60 and 72 Hz. The degree of increase in homologous transcripts was dependent on the signal characteristics.