STRUCTURE OF CHROMATIN IN SEA-URCHIN EMBRYOS, SPERM, AND ADULT SOMATIC-CELLS

Electrophoretic analyses of DNA extracted from micrococcal nuclease partial digests of sea urchin embryo chromatin revealed a DNA repeat length of 222 base pairs for chromatin from morula, mesenchyme blastula, and pluteus stage embryos. No significant differences were observed in the electrophoretic patterns of DNA extracted from micrococcal nuclease limit digests of chromatin from sea urchin embryos at different stages of development; a core fragment containing 140 base pairs of DNA was seen at all stages of embryogenesis examined. Limit digest DNA patterns obtained with sea urchin embryo chromatin were virtually indistinguishable from those obtained with mouse liver chromatin. Furthermore, micrococcal nuclease partial and limit digest DNA patterns of adult sea urchin gut chromatin were identical with those obtained with sea urchin embryo and mouse liver chromatin. These findings suggest that the amount and arrangement of DNA in nucleosomes of sea urchin chromatin remain the same throughout the development of the sea urchin, from embryo to adult. Electrophoretic analyses of DNA extracted from micrococcal nuclease partial digests of sea urchin sperm chromatin revealed a DNA repeat length of 250 base pairs. Limit digest DNA patterns of sea urchin sperm chromatin differed somewhat from patterns obtained with sea urchin embryo and mouse liver chromatin in that they exhibited a major peak at 160 base pairs of DNA, with only a shoulder corresponding to the 140 base pair core fragment. Electrophoretic patterns of DNA extracted from DNase I digests of sea urchin sperm chromatin exhibited the same 10 base interval between DNA fragments as that seen with mouse liver chromatin on denaturing gels. However, while the DNA patterns of DNase I digests of liver chromatin displayed a prominent band at 80 nucleotides, sperm chromatin displayed prominent bands at 70 and 80 nucleotides. Similarly, a comparison of the electrophoretic patterns of DNA extracted from DNase II digests of sea urchin sperm chromatin with those from mouse liver chromatin revealed several significant differences on denaturing gels. These results suggest that the unique histones found in sea urchin sperm chromatin affect both the amount and arrangement of DNA in the nucleosomes of sperm chromatin. © 1979, American Chemical Society. All rights reserved.