Scientists may have to update drawings of the cell’s largest organelle after taking a closer look using higher resolution microscopes.

In a report in the Oct. 28 issue of Science, scientists believe new views of the endoplasmic reticulum using single-molecule super-resolution techniques show tightly packed tubes instead of the plain flat sheets that were previously thought of when viewed under a lower resolution microscope.

Study co-author Jennifer Lippincott-Schwartz, a cell biologist at the Howard Hughes Medical Institute’s Janelia Research Campus told ScienceNews that the findings should help explain how the endoplasmic reticulum reshapes itself in response to changing conditions.

The endoplasmic reticulum is a continuous, membrane-bound organelle, spanning from the nuclear envelope to the outer cell periphery, that contacts and influences nearly every other cellular organelle and is involved in many cellular processes including protein synthesis, calcium storage, mitochondrial division and lipid synthesis and transfer.  

However, determining the dynamic rearrangements and fine ultrastructure of the peripheral ER has proven difficult due to the limitations in imaging technologies.

The closer look at the ER show densely packed tubular arrays instead of the previously proposed flat membrane sheets.

The tubular arrays—being dubbed an ER matrix—can become extremely compact, with spaces between the tubules.

The research team observed the dynamic oscillations of the ER tubules and junctions, with matrices rapidly interconverting from tight to loose arrays, giving rise to different apparent morphologies depending upon how closely their three-way junctions are clustered.

The scientists concluded that the tight clusters of junctions may function as sites for sequestering excess membrane proteins and lipids or for contacting other organelles and that better imagining will continue to shed more light on these functions and processes.

Characterizing ER morphology is particularly important in understanding its roles in basic biology of cells in both health and disease, because mutations in these proteins and resultant ER irregularities coincide with various neurologic disorders, including Alzheimer’s and Parkinson’s diseases.

Study co-author Craig Blackstone, a cell biologist at the National Institute of Neurological Disorders and Stroke, said the discovery will allow doctors to better understand and compare the difference between normal genes and mutations in genes that make ER-shaping proteins cause the symptoms in some patients.

The study can be viewed here.