Atomic force microscopy: A new way to look at chromatin

High-resolution physical techniques such as x-ray crystallography have revealed the nucleosome's structure on the nm scale. However, much less is known about the dynamic nature of nucleosomes and assembled structures in the cell-particularly chromatin structural changes influenced by ionic strength, histone chemical modifications, cell cycle proteins, transcription events, and DNA-binding drugs. Regarding mammalian sperm chromatin, the elemental subunit and higher order packaging structures are not known. Determining the structure of the chromatin in sperm is important to our understanding of the mechanisms involved in DNA condensation, infertility, genomic imprinting, and early events in the egg following fertilization. AFM is a research tool that provides a new way to image and measure uncoated chromatin structures at nanometer-level resolution in ambient air and fluid environments. As shown here, AFM has been successfully applied to studying reconstituted and native chromatin fibers, chromosomes, and sperm chromatin. More clinical and biomedical applications of AFM, such as chromosome karyotyping, chromosome mapping, and human sperm head shape classification and abnormalities have met preliminary success. Therefore, although it is new, AFM has already proved useful in chromatin research. In the future it is anticipated that AFM images acquired under aqueous fluid will become more common and provide exciting new applications and information regarding chromatin structure and function.; High-resolution physical techniques such as x-ray crystallography have revealed the nucleosome's structure on the nm scale. However, much less is known about the dynamic nature of nucleosomes and assembled structures in the cell. AFM is a research tool that provides a new way to image and measure uncoated chromatin structures at nanometer-level resolution in ambient air and fluid environments. Although it is new, AFM has already proved useful in chromatin research.