Current strategies for embryo assessment in the assisted reproductive technology laboratories rely primarily on morphologic parameters that have limited accuracy for determining embryo viability. Even with the addition of invasive diagnostic interventions such as preimplantation genetic testing for aneuploidy alone or in combination with mitochondrial DNA copy number assessment, at least one third of embryos fail to implant. Therefore, at a time when the clinical benefits of single ET are widely accepted, improving viability assessment of embryos is ever more important. Building on the previous work demonstrating the importance of metabolic state in oocytes and embryos, metabolic imaging via fluorescence lifetime imaging microscopy offers new and potentially useful diagnostic method by detecting natural fluorescence of FAD and NADH, the two electron transporters that play a central role in oxidative phosphorylation. Recent studies demonstrate that fluorescence lifetime imaging microscopy can detect oocyte and embryo metabolic function and dysfunction in a multitude of experimental models and provide encouraging evidence for use in scientific investigation and possibly for clinical application.
The outer membrane of Gram-negative bacteria is composed of lipopolysaccharide, a large glycolipid that prevents drugs from entering the cells. Disrupting lipopolysaccharide assembly hypersensitizes bacteria to antibiotics. Sherman et al. used biochemical tools to observe lipopolysaccharide transport. Seven proteins, which are conserved in all Gram-negative bacteria, appear to form a protein bridge that uses adenosine triphosphate to power transport of lipopolysaccharide from one membrane to another. The ability to monitor intermembrane transport of lipopolysaccharide will help in efforts to develop and characterize inhibitors.Science, this issue p. 798Gram-negative bacteria have an outer membrane that serves as a barrier to noxious agents in the environment. This protective function is dependent on lipopolysaccharide, a large glycolipid located in the outer leaflet of the outer membrane. Lipopolysaccharide is synthesized at the cytoplasmic membrane and must be transported to the cell surface. To understand this transport process, we reconstituted membrane-to-membrane movement of lipopolysaccharide by incorporating purified inner and outer membrane transport complexes into separate proteoliposomes. Transport involved stable association between the inner and outer membrane proteoliposomes. Our results support a model in which lipopolysaccharide molecules are pushed one after the other in a PEZ dispenser–like manner across a protein bridge that connects the inner and outer membranes.