DOUBLE-STRANDED INTERNUCLEOSOMAL CLEAVAGE OF APOPTOTIC DNA IS DEPENDENT ON THE DEGREE OF DIFFERENTIATION IN MUSCLE-CELLS

Apoptotic cell death has been correlated to DNA fragmentation into dis crete segments corresponding to the length of nucleosomal protected fr agments of 180-200 base pairs or multiples of it, This DNA degradation has been ascribed to endonuclease activity that cleaves internucleoso mally, thus giving rise to a ladder distribution upon electrophoretic migration. This strict correlation was, however, shown to have notable exceptions, since in some cases only single strand cleavage in the in ternucleosomal DNA regions has been observed (Tomei, D. L,, Shapiro, P , J,, and Cope, O. F. (1993) Proc, Natl. Acad. Sci, U. S. A. 90, 853-8 57), In the present work we show that mouse muscle cells, able to diff erentiate in vitro, if subjected to apoptosis present no DNA degradati on into ladder form unless differentiation is previously induced. Furt hermore, C3H/10T1/2 fibroblast cells, known to undergo apoptosis witho ut DNA ladder formation, if converted to a myogenic program by MyoD ex pression, display internucleosomal DNA degradation upon induction of d ifferentiation.