Nuclear elimination accompanies differentiation in such specialized cell types 
such as erthyrocytes and lens fibre cells. It also accompanies apoptosis which 
has suggested that similar processes could operate in both. Denucleation occurs 
in the lens in order to reduce light scatter and this process is often disrupted 
in cataract. Using the adult bovine lens as a model system, nuclear changes 
accompanying denucleation are described with particular emphasis on the lamina, 
nucleolar and coiled body compartments in lens nuclei. Nuclear shape, chromatin 
reorganization and chromatin breakdown were also monitored to correlate the 
timing of events. Rearrangement of both A- and B-type nuclear lamins occurred in 
parallel with chromatin condensation and preceded changes in nuclear shape. The 
earliest changes detected in this study occurred in the coiled body and 
nucleolar compartments using coilin and fibrillarin antibodies respectively, 
suggesting that a shutdown in transcription is an early event in denucleation. 
Fibrillarin redistributed from an open floret pattern to several condensed spots 
which gradually decreased in intensity and eventually disappeared. Coilin, 
however, was localized in several microfoci prior to being reorganized into 
fewer larger foci. Prior to chromatin condensation, coilin redistributed to the 
nucleolar compartment and was absent from nuclei where chromatin had begun to 
condense. Such nuclei were positive by TUNEL staining. In contrast to the 
nucleus, mitochondrial degradation in lens fibre cells was a rapid process and 
involved a relatively sharp transition between positive and negative fibre cells 
for two mitochondrial specific markers, BAP 37 and prohibitin. A link between 
the changes in the nuclear lamina and chromatin with the initiation of 
mitochondrial fragmentation was also observed. Therefore, it is possible that 
the signal for the initiation of denucleation could originate from the 
mitochondria as proposed for apoptosis. Differences between apoptosis and lens 
fibre cell denucleation were noted and included the timescale of nuclear changes 
as well as the persistence of a nuclear remnant. These studies suggest that 
transcriptional shutdown precedes lamina reorganization and chromatin breakdown 
during lens fibre cell denucleation.