'Magentosis' in human lactating breast: a mode of cell death accumulating single-stranded DNA stretches or breaks

Pale and homogeneous-looking nuclei of degenerative acinar cells selectively seen in an early regression stage of the human lactating breast were periodic acid-Schiff (PAS)-reactive. In our preceding paper, this peculiar morphologic feature was designated as 'magentosis'. The present paper was aimed at histochemically clarifying the nature of the 'magentotic' nuclei. The diffuse PAS reactivity was not influenced by pretreatments with alpha-amylase, DNase, RNase, proteinase K, nor by hydrochloric acid or heating. The nuclei were negative for acid mucosubstances and secretory glycoproteins, and were unreactive with a variety of lectins. In contrast, the presence of single-stranded DNA stretches or breaks was proven. The 'magentotic' nuclei in non-heated paraffin sections were hybridized with a heat-denatured DNA probe for human DNA consensus sequences and were focally immunoreactive with an antibody to single-stranded DNA. The terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) method turned to be positive after digestion by mung bean nuclease, a single-stranded DNA-specific enzyme. The 'magentotic' nuclei were further clearly labeled by the in situ nick translation method. The nucleoli were devoid of reactivity for both the PAS and single-stranded DNA signals. We propose that 'magentosis' represents a unique mode of cell death, distinct from apoptosis and necrosis or oncosis. The PAS reactivity in the 'magentotic' nuclei may be correlated with the occurrence of single-stranded stretches or breaks in the DNA chain.