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.

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.

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.

Continuation of mitosis after selective laser microbeam destruction of the centriolar region

The centriole regions of prophase PTK2 cells were irradiated with a laser microbeam. Cells continued through mitosis normally. Ultrastructural analysis revealed either an absence of centrioles or severely damaged centrioles at the irradiated poles. Microtubules appeared to focus into pericentriolar cloud material.

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.

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.

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.

Argon laser microirradiation of mitochondria in rat myocardial cells in tissue culture. VII. fibrillation in ventricle and auricle cells

Rat myocardial cells in vitro were irradiated in individual mitochondria with an argon ion laser microbeam. The contractile respone termed fibrillation in single and multicellular groups of both ventricle and auricle cells were compared. Specific correlations were made between fibrillation duration, the number of cells in the group, and the number of times the cells had fibrillated. Correlations were also made for the number of laser shots needed to induce fibrillation and the number of cells in the group. Another set of correlations were made between the pre-irradiation beat frequency and the beat frequency following recovery. Several differences and similarities of the above parameters were detected between auricle and ventricle cells. A comparison of the morphology and ultrastructure of auricle and ventricle cells also revealed significant differences.

A possible two-photon effect in vitro using a focused laser beam

A probable two-photon effect is described as a result of focusing an intense pulsed laser beam onto chromosomes of living cells. The effect was suggested after the derivation of a two-photon action spectrum and the demonstration of a lack of reciprocity.

Laser microbeam irradiation of rat kangaroo cells (PTK2) following selective sensitization with bromodeoxyuridine and ethidium bromide

Ethidium bromide (10 mug/ml) and bromodeoxyuridine (25 mug/ml) were used to sensitize selective cell organelles to visible wavelengths of an argon ion laser (488 and 514 nanometers). Ethidium bromide was shown to be selective in sensitizing nucleoli, chromosomes, and the centriolar region of PTK2 cells to the laser microbeam. Similarly, BrDU sensitized chromosomes to the microbeam irradiation. The lesions produced on the chromosomes when either agent was used appeared as a phase paling of the irradiated segment. Nucleolar lesions also appeared as a phase paling, and the centriolar region alteration appeared either as a phase paling or a phase darkening.

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.

Centriole behavior in early mitosis of rat kangaroo cells (PTK2)

Behavior of the centriolar duplexes during early mitosis was investigated. In general, both duplexes are capable of migrating about the cell as a unit with little change in their center to center spacing prior to separation to form the spindle poles. This duplex separation may occur at any point within the mid-prophase-prometaphase period. If it is delayed to prometaphase, transitory monopolar spindles were observed.

Directed chromosome loss by laser microirradiation

In this article I have presented data that indicate the feasibility of attaining the five objectives outlined in the introduction. It should be possible to assign genes to specific chromosome regions by (i) selective DNA deletion of a 0.25- to 0.5-micro.m segment of one or both homologous chromosomes, (ii) deletion of one or both entire homologous chromosomes, or (iii) combining cell fusion with selective deletion of whole chromosomes and then deletion of chromosome segments. By laser microirradiation it should be possible to determine which chromosomes and chromosome regions are essential for immediate cell survival by removing from individual cells whole chromosomes, and chromosome segments from each of the chromosomes in the karyotype, and then assessing the cloning efficiency of each cell. For example, we have already determined that removal of one large chromosome No. 1 from PTK(2) cells does not prevent the cell from undergoing a subsequent mitosis. It should also be possible to generate new classes of mutants by damaging small selected areas of DNA with the laser beam and then cloning the irradiated cells-but this has yet to be demonstrated. This procedure might reveal recessive alleles on the nonirradiated homolog, or might result in the direct production of a genetic mutation. Irradiation of identical places on both homologous chromosomes could result in deletion of a genetic locus which ultimately might be detected as a deficiency in a metabolic pathway or some other cellular abnormality. Studies on chromosome stability and DNA constancy can be conducted with laser irradiated cells. For example, the karyotypic analysis of chromosome No. 1 suggests that a cellular mechanism exists to maintain the constancy of this chromosome in both the diploid and tetraploid cell lines. The same approach could be used with each of the chromosomes in the karyotype. Various cytochemical procedures could be used for making quantitative DNA studies of the cells, and chromosome and DNA analyses could be performed at varying times following laser microirradiation. It might also be possible to study the repair of chromosomal damage caused by laser irradiation. The cells could be examined by autoradiographic, cytochemical, and electron microscopy procedures at varying times after irradiation, and because the precise location, time, and nature of the mutational event would be known, subsequent analysis of repair and alteration would be facilitated.