A pulse BrdU method for SCE

The effect of X-irradiation on cell cycle progression and chromatid aberrations in stimulated human lymphocytes using cohort analysis studies

Stage sensitivity for the production of chromatid-type aberrations and mitotic delay has been investigated in a stimulated human lymphocyte population, following an absorbed dose of 1.5 Gy 250 kVp X-rays. BrdU replication banding was used to obtain a fine analysis of the cell cycle and to permit cohort analysis. Fluctuations in yield with sample time were found for all aberration categories, but these could not be related simply to either the developmental stage of the cells at time of exposure, or to the time-to-run to metaphase. In general G2 and late S cells had higher aberration yields than early S and pre S cell populations. Mitotic delay and perturbation at this dose extends to all sub-phases of S and is as great, if not greater, in the earliest S cells as it is in G2.

A BrdU pulse double-labelling method for studying adaptive response

We describe a pulse BrdU double-labelling method which we have used for a cohort-analysis study of a conventional adaptive response experiment in stimulated human lymphocytes. This method allows us to identify the cycle position occupied by each scored metaphase at the time of primer and at the time of challenge. Responses in cells at defined developmental stages can then be compared irrespective of mitotic perturbation. Using a primer X-ray dose of 1.0 cGy, and a challenge dose of 1.5 Gy 6 h later, we found a transitory depression in frequency of total aberrations present in cells sampled at 6 h but not at 9 h after challenge. When defined cohorts were summed for both sample times, no significant adaptive response was observed. A repeat experiment where terminal BrdU labelling was used after the challenge failed to provide any positive response at either 6 or 9 h. The technique presented not only ensures that similar cell mixtures from a heterogeneous, asynchronous population can be scored and compared, but it serves also to demonstrate the kinetic complexity of stimulated lymphocyte cultures.

BrdU pulse/reverse staining protocols for investigating chromosome replication

By using a reverse Giemsa staining procedure (TT chromatin pale, TB chromatin dark) it is possible to detect replication in metaphase chromosomes with short (approximately 10 min) 5-bromodeoxyuridine (BrdU) pulses. A pulse protocol allows us to consider the question "What is replicating at this point in time?" and we have investigated replication patterns during cycle transit in stimulated human female lymphocytes. A clear-cut demarcation between R-zone early and G-zone late was not found. Instead, whilst replication commences (with a very staggered start) in R-zones, activity soon appears to transgress band boundaries and gives rise to cells with unclassifiable patterns where chromosomes take on a mottled or reticulate appearance. Replication in R-zones dies out leaving a clear G-zone pattern persisting for the remainder of S which terminates with a very staggered finish. When pulse duration is increased (approximately 1 h) the frequency of unclassifiable cells falls and occasional "mixed-pattern" cells appear which have, within the same cell, typical R- and G-zone regions. The existence of such cells indicates that if a mid-S replication pause exists (and the absence of any mid-S wave of pale stained cells suggests that it does not) it does not make exclusive separation between dark R- and G-band zones.