ANALYSIS OF NUCLEAR DEGRADATION DURING LENS CELL-DIFFERENTIATION

Lens cells demonstrate a terminal differentiation process with loss of their organelles including nuclei. Chromatin disappearance is charact erised by the same changes as most apoptotic cells, i.e. condensation of chromatin and cleavage into high molecular weight fragments and oli gonucleosomes. The endo-deoxyribonucleases (bicationic (Ca2+, Mg2+), m ono-cationic (Ca2+ or Mg2+) and acidic non-cationic dependent nuclease s) are present in lens fibre cells. Our results suggest that the acidi c non-cationic nuclease (DNase II) plays a major role in chromatin cle avage. This nuclease, known to be lysosomal, is found in lens fibre nu clei and only an antibody directed against DNase II inhibits the acidi c DNA cleavage of lens fibre nuclei, In addition, there must be anothe r DNase implicated in the process which is not DNase I but appears to be a Ca2+, Mg2+ dependent molecule. Regulation of these DNase activiti es may be accomplished by the effect of post-translational modificatio ns, acidic pH, mitochondrial release molecules, growth factors or onco genes. Finally, fibre cells lose organelles without cytoplasmic elimin ation, The survival of these differentiated cells might be due to the action of survival factors such as FGF 1.