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An essential component of living cells, the nucleolus underwent a major evolutionary shift around 300m years ago.
Scientists have solved an age-old mystery in biology by discovering a protein found in our cells that can explain how a part of the nucleolus – an integral component of cells – evolved.
Loosely formed assemblies known as biomolecular condensates are found in all living cells. While they perform many critical functions, scientists have. until now, not fully understood how proteins and other biomolecules come together to form these assemblies within cells.
In a study published in Cell Reports today (15 August), biologists from Massachusetts Institute of Technology (MIT) say they have discovered a single scaffolding protein that is responsible for the formation of one of these condensates inside the nucleolus.
Known as TCOF1, the protein is essential to the formation of this condensate. Lead authors Nima Jaberi-Lashkari and Byron Lee, both recent MIT PhDs, say the findings could explain a major evolutionary shift in the nucleolus that took place around 300m years ago.
“If you look across the tree of life, the basic structure and function of the ribosome has remained quite static; however, the process of making it keeps evolving,” said Eliezer Calo, an associate professor of biology at MIT and the senior author of the study.
“Our hypothesis for why this process keeps evolving is that it might make it easier to assemble ribosomes by compartmentalising the different biochemical reactions.”
Before the evolutionary shift, the nucleolus – whose role is to help build ribosomes – was divided into two compartments. However, in amniotes such as reptiles, birds and mammals, the nucleolus developed a condensate that acts as a third compartment.
With the latest discovery around the condensate, known as the fibrillar centre, scientists believe they may be able to study its function more easily. The findings also offer insight into how other condensates may have originally evolved in cells.
“Almost every cellular process that is essential for the functioning of the cell has been associated somehow with condensate formation and activity. However, it’s not very well sorted out how these condensates form,” Calo explained.
“More than just creating that condensate, TCOF1 reorganised the nucleolus to acquire tripartite properties, which indicates that whatever chemistry that condensate was bringing to the nucleolus was enough to change the composition of the organelle.”
According to Jaberi-Lashkari, who completed her PhD form MIT this year, what’s most exciting about their work is that it “gives us a molecular handle to control a condensate, introduce it into a species that doesn’t have it and also get rid of it in a species that does have it”.
“That could really help us unlock the structure-to-function relationship and figure out what is the role of the third compartment.”
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