Living organisms are composed of cells, and on the inside of them is cytoplasm, which is about 80 percent water. The cytoplasm is full of a molecular mixture of organelles, proteins, compounds, and other stuff. It was once thought that things moved though cells mostly at random, even though researchers observed the separation of so-called 'colloidal bodies' from the rest of the cytoplasm - then called protoplasm - nearly one hundred years ago. In recent years scientists have begun to learn more about how there is actually organization inside the cell, and that different things can be separated into different areas.
Membrane-less organelles (MLOs) are now known to form inside of cells; these liquid drops lack defined walls but keep certain molecules clumped together. The droplets, which separate from the rest of the cytoplasm like oil in water, help store molecules or collect chemicals together to help trigger chemical reactions that are essential for the cell. Researchers at the University at Buffalo (UB) set out to learn more about how MLOs function.
Priya R. Banerjee, Ph.D., an assistant professor of physics in the UB College of Arts and Sciences and Ashok Deniz, Ph.D., associate professor of integrative structural and computational biology at Scripps Research led the work, which has been outlined in Scientific Reports. They discovered that MLOs seem to be very sensitive to divalent cation levels in cells. Divalent calcium and magnesium ions play crucial roles in cellular signaling. (They are abbreviated Ca2+ and Mg2+ because they are ions with a plus 2 valence or affinity for bonding).
The scientists found that if divalent cations are present in low concentrations, MLOs that harbor proteins and RNA will form. If divalent levels are high, MLOs that only contain RNA will generate.
"It's interesting because you haven't changed the basic ingredients," Banerjee said. "But when you alter the ionic environment, you find that these organelles are highly tunable. They 'switch' from one type to the other, with each type having a distinct internal design." The properties of MLOs are dramatically influenced by divalent cation levels, which may change the function of the MLOs.
In previous work, Banjeree and colleagues investigated a shift in MLOs that makes them less fluid and more like a gel.
"The concept that protein and nucleic acid droplets can function as organelles in a cell has started shifting the paradigm of cell biology that is written in a textbook," Banerjee noted. "Reports started emerging from several different laboratories across the world that MLOs are relevant in gene regulation, protection of cells during stress, immune response and many other biological functions, as well as diseases such as neurological disorders and cancer. Therefore, understanding how MLOs are formed, tuned and altered in diseases are of key importance in the field now."