Original story from the European Molecular Biology Laboratory (EMBL; Heidelberg, Germany). Scientists used 3D images of the human nucleolus to visualize ribosome assembly pathways inside cells for the…
Original story from the European Molecular Biology Laboratory (EMBL; Heidelberg, Germany). Scientists used 3D images of the human nucleolus to visualize ribosome assembly pathways inside cells for the first time. For decades, ribosomes have been, quite literally, under the lens of many scientists. Ribosomes are highly sophisticated and complex molecular machines that allow cells to synthesize proteins. However, putting ribosomes together requires intricate assembly processes.
While many underlying mechanisms for building ribosomes have been discovered ex situ (outside their native cellular context), our understanding of how ribosomes are assembled in situ has so far remained limited. Through a collaboration between the research groups of Christoph Müller, Sara Cuylen-Häring and Julia Mahamid at EMBL Heidelberg, researchers have now pushed these limits.
By combining cryo-electron tomography (cryo-ET) with correlative light and electron microscopy (CLEM), they were able to image the nucleolus – the site of ribosome assembly inside cells – at sufficiently high resolution to visualize the ribosome assembly pathway inside intact human cells for the first time. The results – a mesmerizing collection of molecular snapshots – yielded subnanometer-resolution in-cell structures of tens of intermediates along the ribosome assembly pathways, complementing and expanding previous insights into ribosome assembly obtained from ex situ structures.
Similar methods, new approach EMBL researchers could not rely on traditional structural biology approaches to get a closer look at this complex cellular assembly line. Past studies on pre-ribosome – structural ribosome precursors – employed approaches that required the researchers to take the ribosome components out of the cell. This, in some cases, caused components that only bound each other temporarily to separate.
The difficulty with visualizing this process inside the cell, however, lies in where ribosomes are made: the nucleolus, an extremely dense, low-contrast compartment inside the cell nucleus, which is technically challenging to visualize with cryo-ET. The scientists therefore combined cryo-ET with cryo-CLEM to shed light on these gloomy cellular factories. “Using this combined approach helped us immensely in identifying where this process actually happens,” explained Xiaohan Zhao, first author and Predoctoral Fellow in Müller's group.
This is a source-linked briefing. Read the original report from Biotechniques .