Objective: UPlanSApo 100x oil/1.40	Exposure: 500 ms
Microscope: Olympus DSU/IX81	Gain: 3
Camera: Hamamatsu ImagEM	Interval: 2 s

The rough endoplasmic reticulum is directly continuous with the nuclear envelope and is also studded with ribosomes. In fact, the two organelles are thought to have evolved simultaneously in ancient cells. Due to their physical membranous connection, the lumen of the endoplasmic reticulum and the space between the layers of the nuclear envelope comprise a single compartment. Accordingly, the nucleus has direct access to proteins (many of which are produced by the ribosomes upon its surface) and other materials present in the endoplasmic reticulum lumen, so that transport vesicles are not needed to obtain them. The close association between the endoplasmic reticulum and the nucleus also enables the organelles to share information in a very efficient manner. For instance, if the endoplasmic reticulum begins to undergo functional problems and unfolded proteins accumulate within the organelle, which can be extremely hazardous to the cell, the organelle quickly sends a signal to the nucleus (as well as to the cytoplasm). The nucleus responds by slowing ribosomal translation through a several-step process, thereby giving the endoplasmic reticulum extra time to catch up on its protein folding, thus maintaining cellular health. In the digital video presented in this section, human osteosarcoma cells (U2OS line) expressing enhanced yellow fluorescent protein (EYFP) targeted to the endoplasmic reticulum were imaged with a Hamamatsu ImagEM camera system on a spinning disk confocal microscope.