It has always been a puzzle how cells can so efficiently manage the fusion of intracellular vesicles, such as an (almost) instantaneous release of neurotransmitters from nerve endings or fertilization itself. Now Brown University biologist Gary Wessel and his team made a discovery that lasts less than a millisecond:
Researchers in the Wessel lab are experts in fertilization; they used sea urchin eggs to study membrane fusion. In urchin eggs, thousands of membrane-bound vesicles are attached to the plasma membrane. Within seconds after fertilization, the contents of these vesicles are rapidly released. Previous research has shown that special proteins kept these vesicles tethered to the egg’s membrane. What about the membranes? What do they look like before vesicle cargo is released?
Wessel and his collaborators discovered that the membranes of the egg and the vesicles are hemifused — a state where the membranes are shared but the contents remain separate. Using fluorescent dyes and a high-resolution microscope, the researchers show that hemifusion is surprisingly stable in live cells.
“The novelty of these results is that a live cell can maintain a hemifused state for hours, days, even months,” said Julian Wong, a postdoctoral research associate in the Wessel lab and the first author of the journal article in Developmental Cell. “When using the right cell – the sea urchin egg – the phenomenon is observable.”
“What we’ve found here with membrane fusion is that everything is set and ready for it to occur, to the point of sharing membranes,” Wessel said. “So all that is needed is a puff of calcium from within the cell and fusion is complete. The process is quick because of hemifusion — the vesicles are right there and ready to go.”
Press release: Biologists Prove Critical Step in Membrane Fusion …