The appearance of the chromosomes is very different from what you imagine. New 3D images clarify their structure

Whether you’ve studied biology or not, chances are you’ve come across the artistic / theoretical representation of a chromosome a few times. You know, this X shape (for the X chromosome), now anchored in the memory of most university and high school students following a scientific course. Although researchers have long known that this representation is far from accurate most of the time, imaging technologies to investigate the internal composition of these microstructures have so far been limited. Recently, researchers were able to detail the structure of chromatin (making up chromosomes) using a new very high-resolution 3D imaging technique they have developed.

This popular representation (in X or in Y) is actually that of a chromosome during mitosis (cell division). This is therefore the image given to two joined chromatids after DNA replication, before mitosis is terminated. A moment during which they separated to become their own individual chromosomes.

Unfortunately, this representation poses a problem according to scientists, because this lack of precision would prevent, among other things, the understanding of certain molecular mechanisms. ” In 90% of cases, chromosomes do not exist this way », Explains doctor-scientist Jun-Han Su, formerly of Harvard University.

In a study published this year, Su and her team developed a new way to image the 3D organization of chromatin (within which DNA is packaged and compacted) in human cells, which makes it possible to understand the chemistry of chromosomes in a much more careful way. The results were published in the journal Cell.

« It is very important to determine the 3D organization to understand the molecular mechanisms underlying organization, and also to define how this organization regulates the function of the genome », Explains principal researcher Xiaowei Zhuang.

Colorized 3D view of chromatin, obtained using hybridization in situ by multiplexed fluorescence and very high resolution microscopy. Credit: Xiaowei Zhuang lab

Thanks to a new high-resolution 3D imaging system – which involves bringing together multiple snapshots of genomic loci along DNA chains – researchers were able to visualize chromosomes up close like never before, and even glimpse certain aspects of the transcription activity.

The team has already shared their data online so that other researchers can deepen their analysis, and further explore this (almost) invisible part of the human body. ” We envision wide application of this high throughput, multi-scale, multimodal imaging technology, which provides an integrated view of the organization of chromatin in its native structural and functional context. », Explains the team. Researchers will already be able to characterize so-called “chromatin domains”, compartments and trans-chromosomal interactions and their relationship to transcription in individual cells.

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