The Cell Biology and Metabolism Branch (CBMB) conducts studies in various areas of molecular cell biology, including the mechanisms of intracellular protein trafficking and organelle biogenesis (Juan Bonifacino, Catherine Jackson, Ramanujan Hegde, and Jennifer Lippincott-Schwartz), the regulation of the cell cycle during oogenesis (Mary Lilly), the biology of metal metabolism (Tracey Rouault), and adaptive responses to environmental stresses (Gisela Storz). The CBMB has outstanding microscopy facilities with particular capabilities in light and fluorescence microscopy. Three powerful confocal microscope systems enhance its ability to study cell structure and dynamics by using techniques such as fluorescence imaging in real time, photobleaching, fluorescence resonance energy transfer, fluorescence correlation spectroscopy, and image analysis. In addition, the CBMB has facilities for cell microinjection and micromanipulation, for automated DNA sequencing, and for work with bacteria, yeast, Drosophila melanogaster, and mammalian cells. Members of the CBMB apply knowledge gained from the study of basic cell-biological problems to the elucidation of the causes of human diseases, including disorders of lysosome-related organelles and iron overload.

Over the past year, scientists at CBMB have developed novel fluorescence imaging tools that promise to revolutionize the analysis of protein dynamics within cells. One of these tools is a variant of the green fluorescent protein (GFP) that shows greatly increased fluorescence after activation by light and functions under physiological conditions. Use of this photoactivatable GFP permits the tagging of proteins in a small area of the cell for selective marking by light activation so that a protein’s movement through the cell can be followed against a dark background by fluorescence microscopy. CBMB also developed a novel system, based on fluorescence resonance energy transfer microscopy, to detect changes in the structure and organization of multi-protein complexes of integral membrane proteins in situ. This advance is now being used to visualize directly the spatial organization of protein transport into and out of the endoplasmic reticulum in vivo.

In other studies, CBMB scientists have discovered critical components and interactions of the molecular machinery involved in protein secretion and sorting to different intracellular compartments. The research includes the elucidation of signal-adaptor protein interactions involved in protein sorting to lysosomes and the identification of interaction partners for guanine nucleotide exchange factors for the Arf family of small GTPases. A genomic screen resulted in the identification of many new genes involved in the biogenesis of the yeast vacuole and mammalian lysosomes. The scientists also discovered a new protein complex that is defective in mutant mouse models of the pigmentation and bleeding disorder Hermansly-Pudlak syndrome.

Another CBMB group found that ablation of genes encoding iron-regulatory proteins in mice cause accumulation of iron in certain regions of the brain, with progressive development of a neurodegenerative disorder. This finding suggests a possible connection between iron overload and other neurodegenerative disorders of unknown etiology. Other studies identified important cellular regulators of oocyte development in the ovary and of the response to oxidative stress mediated by the small RNA OxyS.