Superresolution methods reveal new picture of the endoplasmic reticulum

With emerging superresolution microscopy techniques, biologists can get more detailed pictures of structures they thought they already understood. The most recent biological structure to yield its secrets is the endoplasmic reticulum. The ER, which stretches from the nuclear envelope to the edges of a cell, is home to many biological processes, including protein and lipid synthesis. In conventional microscopy images, the peripheral portions of the ER appear to include flat membrane sheets. But that picture is wrong, according to a new study led by Jennifer Lippincott-Schwartz of Howard Huges Medical Institute’s Janelia Research Campus and Craig Blackstone of NIH (Science 2016, DOI: 10.1126/science.aaf3928). To probe the ER in multiple types of cells, the team used four superresolution optical microscopy methods, which provide images at a resolution that exceeds conventional microscopy limits, as well as focused ion beam scanning electron microscopy. With these methods, the researchers observed that the peripheral ER is actually made of a dense matrix of tubes instead of flat membrane sheets. They acquired images fast enough to observe the tiny tubes undergoing rapid movement and interconversion between tight and loose arrays. The tube organization may allow the ER to rapidly change its conformation as necessary to perform its many functions, the researchers speculate.