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Related Experiment Videos

Changes in DNA topology during spermatogenesis.

M S Risley, S Einheber, D A Bumcrot

    Chromosoma
    |January 1, 1986
    PubMed
    Summary
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    Sperm DNA topology changes during development. Histone replacement in some species leads to DNA unfolding and loss of negative supercoils, mediated by nonbasic nuclear proteins.

    Area of Science:

    • Molecular Biology
    • Genetics
    • Cell Biology

    Background:

    • DNA in eukaryotic cells is organized into topologically constrained domains.
    • During spermatogenesis, histones are replaced by protamines, altering DNA packaging.
    • The role of these changes in DNA topology during spermiogenesis is not fully understood.

    Purpose of the Study:

    • To investigate alterations in DNA topology during spermatogenesis.
    • To determine if DNA supercoiling changes as histones are replaced by protamines.
    • To explore the role of nonbasic nuclear proteins in sperm DNA organization.

    Main Methods:

    • Studied DNA topology in histone- and protamine-depleted nuclei (nucleoids) from various cell types.
    • Measured DNA expansion/contraction using fluorescence microscopy with increasing ethidium bromide concentrations.

    Related Experiment Videos

  • Assessed DNA relaxation using UV light, DNase I, proteinase K, urea, RNase A, and dithiothreitol.

    • Main Results:

    • Nucleoids from somatic cells, spermatocytes, and spermatids showed negatively supercoiled DNA.
    • Xenopus and Bufo sperm nucleoids displayed relaxed DNA at low ethidium bromide concentrations, condensing at higher concentrations.
    • Sperm nucleoid DNA condensation was reversed by UV light, DNase I, proteinase K, or urea, indicating protein involvement.

    Conclusions:

    • Histone replacement by protamines in Xenopus and Bufo sperm is linked to DNA unfolding and loss of negative supercoils.
    • Nonbasic nuclear proteins in sperm constrain DNA into supercoiled domains.
    • These proteins play a role in nuclear morphogenesis and DNA arrangement during spermiogenesis.