A note on the decreased number and loss of fibrillar centres in nucleoli of apoptotic HL-60 leukaemic granulocytic precursors produced by 5-aminolaevulinic acid-based photodynamic treatment.

The nuclear and nucleolar ultrastructure was studied by means of conventional transmission electron microscopy to provide more and complementary information on nucleolar changes accompanying the apoptotic process in leukaemic granulocytic precursors (HL-60 cells) produced by PDT without previous terminal differentiation. PDT induced the apoptotic process using BL irradiation and ALA as a precursor of the photosensitizer protoporphyrin IX. PDT produced marked changes of the nucleolar ultrastructure in apoptotic cells, such as reduction of the number and loss of fibrillar centres surrounding dense fibrillar components. Such nucleolar changes are known to reflect an alteration of nucleolar biosynthetic activities, which are believed to be located at the periphery of fibrillar centres. Some electron micrographs also indicated that fibrillar centres apparently migrated out from nucleolar bodies.