As Sykes explains, the Holy grail of transplantation is tolerance, the long-term graft acceptance without the long-term use of immunosuppressants. Sykes and collaborators developed a hematopoietic cell transplantation and mixed chimerism technique that proved to induce true tolerance in humans. They showed that transient mixed chimerism, the co-existence of donor and recipient hematopoietic elements, was detected in patients where tolerance was observed. Sykes reviews the clinical trial results and explains the experimental techniques used to study the molecular features that predict tolerance and low rates of organ rejection in patients.

Spudich describes the technological and experimental advances of the last ~50 years that have allowed researchers to understand muscle contraction in molecular detail. The development of an in vitro assay let Spudich and his colleagues determine which domain of the myosin molecule (which is very large) is necessary for movement. A laser trap assay allowed them to measure the size of the “step” taken by a myosin molecule moving along actin, as well as the force generated by a single myosin molecule. The solution of a crystal structure for myosin also provided key information about its mechanism of action. These results, together with early enzymatic analysis, have led to a detailed molecular model for the chemo-mechanical cycle of myosin.

Spudich recounts his first foray into muscle research as a postdoc in Hugh Huxley’s lab. He wanted to understand how Ca2+ regulated muscle contraction via the troponin/tropomyosin complex. Using electron micrographs and diffraction analysis to investigate where tropomyosin filaments lie along actin filaments, Spudich showed that tropomyosin filaments block the myosin-binding sites on actin. When muscle is stimulated, Ca2+ is released from intracellular stores and binds to troponin causing tropomyosin to move. This allows myosin to bind to actin and the muscle to contract. These finding led Spudich and Huxley to propose a steric blocking mechanism for regulation of muscle contraction. Recent technological improvements have confirmed this model and filled in important details.

Spudich focuses on current studies in his lab to understand how mutations in cardiac myosin cause human hypertrophic cardiomyopathy (HCM). This is a disease characterized by a hyper-contractile heart and is the most common cause of sudden cardiac arrest in people under 35 years old. Based on insight from a dream, Spudich realized that many of the mutations associated with HCM are in a region of the myosin molecule (the myosin mesa) that may regulate the availability of myosin heads to bind to actin and thus, regulate muscle contraction. Spudich’s lab is now working to determine the importance of the myosin mesa in regulating cardiac contractility and, in particular, its role in HCM.

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.

 Seydoux explains how the PAR domains reorganize other proteins in the cytoplasm of the one-cell embryo and creates a body axis. MEX-5 is an RNA-binding protein that localizes to the anterior side of the embryo, forming a concentration gradient in the cytoplasm. Excitingly, her lab discovered that the MEX-5 gradient is caused entirely by the difference in diffusion rates between two MEX-5 species! The shift between the two species is controlled by PAR-1-mediated phosphorylation. This simple mechanism explains how a protein can become localized to a particular area of the cell without directed transport.

During development, how do embryos distinguish their posterior (tail) versus anterior (head)? Dr. Geraldine Seydoux’s lab uses the small worm C.elegans as a simple model to study this question. In her first video, she introduces how the sperm divides the egg into distinct anterior and posterior domains shortly after fertilization to create the body axis. Her lab discovered that the sperm introduces microtubules that reorganizes the distribution of a network of polarity regulators, called PAR proteins. The PAR proteins segregate into two non-overlapping domains that define the anterior and posterior axis of the worm.

Schekman outlines exosome biogenesis. Exosomes are extracellular vesicles released by the cell, and in contrast to intracellular vesicles, exosomes contain small molecules of RNA. Schekman’s laboratory characterized the RNAs contained in exosomes and showed the importance of Ybx1 protein for the recruitment of certain miRNAs into exosomes.

Schiller discusses the high efficacy of HPV vaccine, which is exceptionally good at producing neutralizing antibodies and also benefits from the low mutation rate of HPV. Coming to a better understanding of the efficacy of the HPV vaccine will provide evidence to support single-dose vaccination and aids in the development of new vaccines.

Human Papillomavirus (HPV) causes 5% of all cancers worldwide, and the first vaccine against HPV was approved in 2006. In this seminar, Dr. John Schiller provides an overview of HPV virus and infection, compares the three FDA approved vaccines against HPV, and explains the endpoints used in the clinical trials to prove vaccine efficacy. After a decade of using the vaccine, retrospective studies now allow us to evaluate the possibility of using single-dose vaccination, which could lead to an increase in the general use of the vaccine (implementation), and improve HPV-related cancer prevention.