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Biomedical subjects

M W Berns

Publications and source records attributed to M W Berns.

At least 19 recordsLinked to original sources
PubMed1979

Genetic microsurgery by laser: establishment of a clonal population of rat kangaroo cells (PTK2) with a directed deficiency in a chromosomal nucleolar organizer.

An ultraviolet laser beam was focused to a submicron spot on one of the nucleolar organizer regions of mitotic chromosomes of rat kangaroo cells in tissue culture. The daughter cells were isolated and cloned into a viable population that maintained the directed nucleolar deficiency. It is concluded that the laser can be used to delete preselected genetic regions and the genetic deletion is maintained as a heritable deficiency in subsequent daughter cells.

Animals↗
PubMed1979

Fluorescence analysis of cells using a laser light source.

A quantitative microfluorometric instrument is described that employs a helium cadmium laser (442 nm) as the illumination source. The instrument consists of a double grating monochromator in front of a gallium arsenide photomultiplier that is interfaced with a desktop computer. The versatility of the instrument in making quantitative nucleic acid measurements on acridine orange and Feulgen-Schiff stained cells is demonstrated. The ploidy levels of several populations are easily determined, and the Feulgen fluorescent emissions are considerably greater than those obtained with a standard mercury lamp.

Animals↗
PubMed1979

Electrical activity of rat myocardial cells in culture: La3+-induced alterations.

Intracellular analysis of neonatal rat (1-2 day old) ventricular cells in culture shows that contracting myocardial cells exhibit an array of different patterns of spontaneous electrical activity. Resting membrane potentials varied between -40 mV and -98 mV. Our results indicate that some cultured cells show resting membrane potentials, overshoot, and total spike amplitude values comparable to those normally found in neonatal and adult rat heart. A low ratio of pacemaker (40%) to nonpacemaker cells (60%) and low incidence of hyperpolarizing after-potentials (35%) were found. La3+ application (0.1-4.0 mM) induced progressive cell depolarization, concomitant diminution in discharge frequency, and marked alteration of action potential configuration. A parallel decline in frequency and strength of rhythmic contractions was observed. Abolition of contractility occurred only in association with depolarization and complete disappearance of action potentials. Recovery of electrical and contractile activity followed medium replacement. Our results indicate that La3+ does not act as a specific excitation-contraction (E-C) uncoupler in the cultured cells but has multiple effects upon their normal electrical characteristics.

Action Potentials↗
PubMed1978

Chromatin influence on the function and formation of the nuclear envelope shown by laser-induced psoralen photoreaction.

Potorous tridactylis (PTK2) cells growing in culture were treated with psoralen derivatives and dividing cells were located by phase-contrast microscopy. Psoralens, light-sensitive DNA-photoadducting drugs, were reacted with mitotic chromosomes through exposure to 365-nm light from an argon laser microbeam system. It was found that following mitosis and photoreaction, cells without nuclear envelopes were produced when psoralen-treated cells received 60 light pulses over their entire chromosome complement. These 'non-nuclear membrane' cells were found to incorporate [3H]uridine and, to a lesser extent, [3H]thymidine by autoradiography. Reduction of the light exposure by half (30 near-u.v. pulses) over the entire chromosome complement in the presence of psoralen also produced non-nuclear-membrane cells as seen by light microscopy. Further examination of these cells (30 light pulses) by single-cell electron microscopy revealed that unlike the high light exposure (60 near-u.v. pulses), the low light dosage resulted in cells with membrane patches associated with their chromatin. Since neither actinomycin D nor cycloheximide impeded nuclear envelope reformation, the psoralen-DNA reaction is concluded to produce non-nuclear-membrane cells by a mechanism other than transcription or translation inhibition. The association of Golgi with areas of nuclear membrane patches gives indirect evidence of a possible Golgi contribution to the reformation of the nuclear envelope after mitosis. It is concluded that DNA plays a role in envelope reformation.

Animals↗
PubMed1978

Evidence for centriolar region RNA functioning in spindle formation in dividing PTK2 cells.

The light-activated, nucleic acid-binding drugs, psoralens, were used in conjunction with a 365-nm laser microbeam to selectively bind to any nucleic acids in the centriolar region. 4'-aminomethyl-4,5',8--trimethyl-psoralen (AMT) has a high affinity for both RNA and DNA and can be shown to cause mitotic abortion when centriolar regions of prophase PTK2 cells and reacted with AMT and 365-nm laser light. Other psoralen derivatives which have a high affinity for DNA and a low affinity for RNA are not effective in blocking mitosis in dividing PTK2 cells. Examination of psoralen-bound centriolar regions by single-cell electron microscopy shows that at various times after treatment, the number of microtubules associated with the irradiated poles is much lower than in normal, dividing cells. Light-activated psoralen binding of the centriolar regions does not seem to affect the condensation or structure of mitotic chromosomes. It is concluded that there is an RNA in the centriolar region that is responsible for the formation of the spindle in dividing cells.

Cells, Cultured↗
PubMed1977

Alteration of membrane electrical activity in rat myocardial cells following selective laser microbeam irradiation.

Laser microirradiation of neonatal rat (1 to 2-day-old) ventricular cells in tissue culture results in overt changes in contractility. The intracellular study of their ongoing electrical activity prior to, during, and after laser microirradiation demonstrates that definite membrane alteration occurs concomitantly with induced contractile responses. Although all ventricular cells are depolarized by laser microirradiation, the ultimate response elicited seems to differ according to the type of myocardial cell impaled. Typical fibrillation potentials were induced mainly in pacemaker cells.

Action Potentials↗
PubMed1977

The role of the centriolar region in animal cell mitosis. A laser microbeam study.

An argon ion laser microbeam (488 and 514 nm) was used to selectively irradiate one of the two centriolar regions of rat kangaroo Potorous tridactylis (PtK2) prophase cells in vitro. The cells were sensitized to the laser radiation by treatment with acridine orange (0.1-0.2 mug/ml). Ultrastructural examination of the irradiated centriolar regions demonstrated that the primary site of damage was the pericentriolar material. This result suggests that nucleic acid is present in the pericentriolar material. Behavioral and ultrastructural analysis demonstrated that cells with one damaged pericentriolar zone could undergo (a) nuclear membrane breakdown, (b) chromosome condensation, (c) metaphase plate formation, and (d) cytokinesis. However, the chromosomes neither separated nor exhibited any anaphase movements. Detailed ultrastructural analysis revealed the presence of kinetochore microtubules on both sides of chromosome mass and a lack of microtubules in the cytokinesis constriction. These results indicate that the pericentriolar material is important in spindle orgainization and essential for the formation of the interpolar microtubules.

Cell Line↗
PubMed1977

The absence of centrioles from spindle poles of rat kangaroo (PtK2) cells undergoing meiotic-like reduction division in vitro.

Light and electron microscopy were used to study somatic cell reduction division occurring spontaneously in tetraploid populations of rat kangaroo Potorous tridactylis (PtK2) cells in vitro. Light microscopy coupled with time-lapse photography documented the pattern of reduction division which includes an anaphase-like movement of double chromatid chromosomes to opposite spindle poles followed by the organization of two separate metaphase plates and synchronous anaphase division to form four poles and four daughter nuclei. The resulting daughter cells were isolated and cloned, showing their viability, and karyotyped to determine their ploidy. Ultrastructural analysis of cells undergoing reduction consistently revealed two duplexes of centrioles (one at each of two spindle poles) and two spindle poles in each cell that lacked centrioles but with microtubules terminating in a pericentriolar-like cloud of material. These results suggest that the centriole is not essential for spindle pole formation and division and implicate the could region as a necessary component of the spindle apparatus.

Cell Line↗
PubMed1976

Nucleoli and ploidy in Potorous cells (PTK2) in vitro.

Most cells of the male PTK2 cell line contain one nucleolus, and they are diploid. However, a proportion of cells have more than one nucleolus. Cells with two and three nucleoli were isolated and cloned into viable populations. Greater than 90% of the cells in these clonal populations maintained the abnormal nucleolar number of the originally isolated cell. Karyotype analysis of cells with two and three nucleoli demonstrated that the cells were respectively tetraploid and hexaploid. It was concluded that in PTK2 cells, nucleolarity is a good index of ploidy even if the ploidy level is abnormal. Furthermore, long term monitoring of the tetraploid cells demonstrated virtually no tendency towards reversion to the diploid condition as suggested by other studies in Potorous.

Animals↗