We have optimised an indirect immunoperoxidase technique demonstrating bromodeoxyuridine (BrdU) incorporation into dividing cells for cerebellar tissue sections of four-day-old rats injected with this marker. This permits confident identification of granule-cell precursors engaged in DNA synthesis in the external granular layer of the developing cerebellum. Preservation of BrdU immunoreactivity is attained using methanol/acetic acid fixation and different pretreatments before immunostaining, while unlabeled nuclei can be recognized clearly after Feulgen or hematoxylin counterstaining. We established conditions to ensure satisfactory BrdU uptake without affecting cell-cycle progression during the postlabeling time period. The dose of BrdU employed provides saturation S-phase labeling from at least 1 h after BrdU delivery. Various kinetic parameters and phase durations have been determined in experiments involving a single injection or cumulative labeling sequences, and the cycle time was calculated based on two models of generative behavior: steady-state and exponential growth. The working hypothesis of steady-state kinetics can be adopted successfully if the existence of neuroblasts with different proliferation rates is taken into account.

The use of bromodeoxyuridine (BrdU) and subsequent immunocytochemical visualization for studying cell proliferation in plant meristems was investigated in Allium cepa L. root-tips. We describe the optimization of an indirect immunoperoxidase method for detecting incorporation of this DNA precursor in pulse-labeled cells. The basic object of this study is to quantify the extent to which the fraction of S-phase cells can reliably be estimated in asynchronous populations. A matrix of parallel labeling schedules with tritiated-thymidine or BrdU was developed, and the labeling indices provided by autoradiography or immunocytochemistry were compared. Thus, 0.5 mM BrdU assured saturation S-phase labeling after an exposure time of 30 min, and the mean length of the S-phase determined under such conditions was similar to that previously reported for this plant system. Interestingly, Feulgen staining did not interfere with subsequent detection of the BrdU probe. This allowed comparative evaluations of the nuclear DNA content by Feulgen-microdensitometry and the position of a given cell in G1, S or G2 compartments. We also explored the possibility of quantifying BrdU-incorporation in single nuclei by densitometry measurement of the peroxidase label.

We have optimised an indirect immunoperoxidase technique demonstrating bromodeoxyuridine (BrdU) incorporation into dividing cells for cerebellar tissue sections of four-day-old rats injected with this marker. This permits confident identification of granule-cell precursors engaged in DNA synthesis in the external granular layer of the developing cerebellum. Preservation of BrdU immunoreactivity is attained using methanol/acetic acid fixation and different pretreatments before immunostaining, while unlabeled nuclei can be recognized clearly after Feulgen or hematoxylin counterstaining. We established conditions to ensure satisfactory BrdU uptake without affecting cell-cycle progression during the postlabeling time period. The dose of BrdU employed provides saturation S-phase labeling from at least 1 h after BrdU delivery. Various kinetic parameters and phase durations have been determined in experiments involving a single injection or cumulative labeling sequences, and the cycle time was calculated based on two models of generative behavior: steady-state and exponential growth. The working hypothesis of steady-state kinetics can be adopted successfully if the existence of neuroblasts with different proliferation rates is taken into account.