Researchers at the University of Chicago have new evidence to support a controversial theory about tiny intracellular structures called organelles. Their findings support the theory that certain organelles form an interconnected system where one organelle gives rise to another through outgrowths of its own membrane.
Their discoveries will also shed light on disorders such as Menkes disease and polycystic kidney disease, which are caused by defects in Golgi function.
The researchers studied a particular region of the cell where an organelle called the endoplasmic reticulum (ER) seems to give rise to another organelle called the Golgi apparatus. This process occurs at specific places along the ER called transitional ER (tER) sites.
"Our work strongly suggests that the Golgi apparatus grows directly out of the tER," says Benjamin Glick, assistant professor at the University of Chicago and lead author of the paper in the April 5 issue of the Journal of Cell Biology.
The Golgi apparatus, which consists of a stack of pancake-shaped membranes called cisternae, is responsible for modifying and packaging proteins for export to the cell surface. According to the membrane outgrowth theory, Golgi cisternae are transient structures, with new cisternae constantly being generated at tER sites.
Glick realized he had a unique opportunity to test this hypothesis when he noticed very different-looking Golgi formations in two yeast species: Pichia pastoris, which has the typical coherent stacked Golgi cisternae, and Saccharomyces cerevisiae, or brewer's yeast, which has dispersed individual cisternae scattered throughout the cell.
"We used these two yeasts because they are closely related, yet they
have completely different Golgi structures. Saccharomyces is definitely an
oddity because almost every other kind of cell has well-organized Golgi stacks.
We reasoned that the dispersed Golgi in Saccharomy
Contact: Sharon Parmet
University of Chicago Medical Center