iBiology Videos

Witkin provides a historical perspective on how working at Cold Spring Harbor (CSH) shaped her scientific career and led to the discovery of the SOS DNA damage response in bacteria. At CSH she worked with the pioneers of bacterial genetics, at a time when there was a major discovery every other week. As a PhD student Witkin observed that some bacteria were able to survive high doses of UV radiation. She speculated that these bacteria may have a mechanism to repair DNA making them UV resistant. These revolutionary ideas gave birth to the discovery that cells have a mechanism to repair DNA damage, the SOS response.

In the past decade there has been an amazing change in the efficiency of DNA sequencing. Using traditional Sanger sequencing, the human genome project took 20 years and cost $3 billion. Current next generation sequencing methods allow a human genome to be sequenced for $1000, in 48 hours!  In this talk, Eric Chow explains the chemistry behind next generation sequencing, and describes how the next gen sequencers detect and display results. The most commonly used Illumina sequencers are image based and detect the addition of fluorescently labelled nucleotides. Chow also describes two different next generation sequencing technologies which provide benefits such as much longer reads but with downsides such as higher error rates. Chow finishes the talk with some insights into medical applications of next gen sequencing such as much less invasive prenatal testing or cancer detection.

Dr. Spudich begins his talks with a clear overview of muscle biology. Muscles are made of many cells and each cell contains many contractile units called sarcomeres. Sarcomeres are made of parallel filaments of two different proteins, actin and myosin. The filaments slide relative to each other and cause the sarcomere, and in turn the muscle, to contract. Spudich recounts the breakthroughs that led muscle biologists to propose this sliding filament model (~1950). By 1969, experiments using electron microscopy, a relatively new technology at the time, and X-ray diffraction, had advanced the model to explain how the “swing” of individual myosin molecules along actin filaments could power muscle contraction.

When he was a graduate student, Dr. Ruslan Medzhitov read a theory written by Dr. Charles Janeway that foresaw the existence of a set of receptors that would directly detect pathogens and signal to T- and B-cells to generate an immune response (adaptive immunity). Medzhitov was determined to find such receptors! In this discovery talk, Dr. Ruslan Medzhitov provides a historical perspective that frames his involvement in the discovery of Toll-Like Receptors. By following the clue that NF-kB was involved in the immune response, he searched for receptors, like Toll, that had the capacity to activate NF-kB.

Apicomplexa are evolutionarily distinct eukaryotes that play an important role in human diseases such as toxoplasmosis and malaria. So how do scientists study their unique biology? Dr. Sebastian Lourido explains that his lab uses Toxoplasma gondii as a model to study the phylum Apicomplexa. In part one of his talk, he explains the complex life cycle of T. gondii and he describes the unique organelles found in apicomplexa and used to facilitate invasion, survival and replication inside host cells. He highlights research from his lab demonstrating the importance of calcium signaling for T. gondii invasion.

Ostrander explains that canine genetics can be used to understand disease susceptibility and cancer risk. By analyzing the pedigree of dogs, her laboratory identified a series of genes involved in the elevated cancer risk of particular dog breeds. Specifically, her laboratory studied invasive transitional cell carcinoma of the bladder, a disease for which breeds like Scottish Terriers have a high susceptibility.  In human cases of this disease, the cause is unknown in 50% of patients. Ostrander’s laboratory identified genetic mutations that explain the elevated cancer risk in these dogs. This information may improve diagnosis and targeted therapy in dogs and humans.

Although all domestic dogs belong to the same species, different breeds display unique morphological traits and different disease susceptibility. Dr. Elaine Ostrander provides an overview of canine genetics, and explains how scientists are using genetics to decipher the molecular basis of different traits such as height and cancer risk.

Hegde explains that although the protein localization system usually operates accurately, it does sometimes fail.  This can be due to genetic mutations, stress within an organelle, or just intrinsic inefficiencies that accompany any complex process. As a graduate student, Hegde used a cell-free in vitro system to study the translocation of prion protein into the ER. He found that a small amount of prion protein did not completely cross the ER membrane as expected, but remained in a transmembrane form. Worried that this was an artifact of the in vitro system, he designed experiments in mice to see what the effect of an increase in mislocalized, transmembrane prion protein would be. He found a striking result - even a small increase in the amount of transmembrane prion protein caused increased neurodegeneration in mice. It turns out that incomplete translocation is not unique to prion protein. Hegde tells us how, as an independent investigator, his lab went on to investigate why this happens and how the cell monitors and degrades proteins that are not properly localized.

Proteins that are secreted from the cell or localized to the plasma membrane need first to be translocated into the lumen of the ER or inserted into the ER membrane. Thousands of proteins, each with a unique signal sequence, move through this pathway. How does the protein translocation machinery recognize these diverse signals and correctly localize the protein?  In his third talk, Hegde describes studies from his lab using cryo-electron microscopy to visualize the translocation machinery at different stages in the recognition and engagement of a secreted or membrane inserted protein. The structural information gleaned from these experiments helps to explain how the protein translocation machinery works with high fidelity even when it needs to recognize diverse signal sequences.

Cells are organized into many different compartments such as the cytosol, nucleus, endoplasmic reticulum (ER), and mitochondria. Almost all proteins are made in the cytosol, yet each cellular compartment requires a specific set of proteins.  How does the cell regulate protein localization to be sure that proteins end up where they should? In his first lecture, Manu Hegde reviews the history of this field and highlights key experiments that have led to our current understanding of how protein localization occurs.