CHROMOSOME DIMINUTION IN ASCARIS-SUUM - 2-FOLD INCREASE OF NUCLEOSOMAL HISTONE TO DNA RATIOS DURING DEVELOPMENT

The swine intestinal nematode A. suum eliminates chromatin material from its primordial somatic cells during early embryogenesis. A technique for isolation of nuclei from pre- and post-diminution stage embryos was developed and these isolated nuclei were used in investigations of nuclear events during diminution. The amount of DNA per nucleus determined by diphenylamine assays and isotope dilutions was 0.66 pg and 0.29 pg in pre- and post-diminution nuclei, respectively. A. suum loses 56% of its nuclear DNA during diminution. The loss of nuclear DNA enabled in vivo examination of histone/DNA ratios as a function of changes in DNA quantities. A. suum histones were identified by acid exrtactability and tryptic fingerprint comparison with rat liver histones. Measurement of histone quantities was accomplished using linearity of Coomassie blue binding to histones separated in dodecyl sulfate gels. A. suum nucleosomal histones levels were relatively constant in pre- and post-diminution nuclei. Nucleosomal histone/DNA ratios approximately doubled during diminution.