The immune system is responsible for fighting infection and disease. It is comprised of many specialized cell types, all which work together to keep people healthy. In this short video, Dr. Brittany Anderton introduces the cells of the immune system. She compares and contrasts innate and adaptive immunity, and lays out the molecular interactions required to activate each type of response.

Brangwynne tells us about recent work in which his lab has used light to control phase separation behavior in cells. By linking IDRs from proteins that are known to phase separate to protein domains that weakly oligomerize in response to light, his lab has generated tools that are allowing them to investigate the role of phase separation in different cell processes in many cell types.  

Brangwynne focuses on the formation of the nucleolus; one of several membrane-less bodies found in the nucleus. Brangwynne’s lab was able to show that assembly of the nucleolus also can be described by the physics of phase separation.

How do the tiny, crowded, constantly moving molecules inside of cells come together to form functional structures such as organelles? Dr. Cliff Brangwynne explains that many of the organelles we are familiar with, such as the nucleus and the Golgi apparatus, are membrane bound. However, some organelles, such as P granules and nuclear bodies, are not surrounded by a membrane. 

Förster Resonance Energy Transfer (FRET) microscopy is a technique that allows monitoring of interactions between dyes that occur on the nanometer scale. This sensitivity to small changes in distance and orientation make it a popular technique for building biosensors. Here, Philippe Bastiaens describes the physics behind FRET and how FRET can be measured with a microscope.

Sabatini explains that mTORC1 responds to many different upstream signals including a variety of growth factors, nutrients, and types of stress. 

Sabatini focuses on a lysosomal membrane protein that his lab had found to interact with mTORC1 and to sense arginine levels inside the lysosome. In some cell types, the amino acids needed to build new proteins are not taken up as free amino acids but instead come from the breakdown of proteins in the lysosome. This led the lab to ask which arginine-rich proteins are being degraded in the lysosome, which led to the realization that ribosomal proteins are amongst the most arginine-rich proteins in mammalian cells. After many more experiments, they showed that mTORC1 regulates a balance between the biogenesis of ribosomes, and the breakdown of ribosomes (known as ribophagy), dependent on the nutritional state of the cell.  Ribophagy seems to be particularly important for supplying the cell with nucleosides during nutrient starvation.