Nanoscale architecture of integrin-based cell adhesions.

Cell adhesions to the extracellular matrix (ECM) are necessary for morphogenesis, immunity and wound healing. Focal adhesions are multifunctional organelles that mediate cell-ECM adhesion, force transmission, cytoskeletal regulation and signalling. Focal adhesions consist of a complex network of trans-plasma-membrane integrins and cytoplasmic proteins that form a <200-nm plaque linking the ECM to the actin cytoskeleton. The complexity of focal adhesion composition and dynamics implicate an intricate molecular machine. However, focal adhesion molecular architecture remains unknown. Here we used three-dimensional super-resolution fluorescence microscopy (interferometric photoactivated localization microscopy) to map nanoscale protein organization in focal adhesions. Our results reveal that integrins and actin are vertically separated by a ∼40-nm focal adhesion core region consisting of multiple protein-specific strata: a membrane-apposed integrin signalling layer containing integrin cytoplasmic tails, focal adhesion kinase and paxillin; an intermediate force-transduction layer containing talin and vinculin; and an uppermost actin-regulatory layer containing zyxin, vasodilator-stimulated phosphoprotein and α-actinin. By localizing amino- and carboxy-terminally tagged talins, we reveal talin's polarized orientation, indicative of a role in organizing the focal adhesion strata. The composite multilaminar protein architecture provides a molecular blueprint for understanding focal adhesion functions.

A genetically encoded tag for correlated light and electron microscopy of intact cells, tissues, and organisms.

Electron microscopy (EM) achieves the highest spatial resolution in protein localization, but specific protein EM labeling has lacked generally applicable genetically encoded tags for in situ visualization in cells and tissues. Here we introduce "miniSOG" (for mini Singlet Oxygen Generator), a fluorescent flavoprotein engineered from Arabidopsis phototropin 2. MiniSOG contains 106 amino acids, less than half the size of Green Fluorescent Protein. Illumination of miniSOG generates sufficient singlet oxygen to locally catalyze the polymerization of diaminobenzidine into an osmiophilic reaction product resolvable by EM. MiniSOG fusions to many well-characterized proteins localize correctly in mammalian cells, intact nematodes, and rodents, enabling correlated fluorescence and EM from large volumes of tissue after strong aldehyde fixation, without the need for exogenous ligands, probes, or destructive permeabilizing detergents. MiniSOG permits high quality ultrastructural preservation and 3-dimensional protein localization via electron tomography or serial section block face scanning electron microscopy. EM shows that miniSOG-tagged SynCAM1 is presynaptic in cultured cortical neurons, whereas miniSOG-tagged SynCAM2 is postsynaptic in culture and in intact mice. Thus SynCAM1 and SynCAM2 could be heterophilic partners. MiniSOG may do for EM what Green Fluorescent Protein did for fluorescence microscopy.

Confocal microscopy on the Internet.

In a few short years, the Internet (in terms of the World Wide Web) has become a powerful informational resource for the original scientific literature pertaining to biological investigations using the laser scanning confocal microscope. However, there still remains an obvious void in the development of educational Web sites targeted at beginning students and novices in the field. Furthermore, many of the commercial aftermarket manufacturers (for example, those offering live-cell imaging chambers) have Web sites that are not adequately represented in published compilations, and are therefore somewhat difficult to locate. In order to address this issue, several educational sites dedicated to optical microscopy and digital imaging that are being constructed and hosted at The Florida State University are currently turning their attention to the increasing application of confocal microscopy in the biological and materials sciences. The primary focus of this effort is to create new sections on the existing sites that address the important educational issues in confocal microscopy, as well as creating indices of links to both the confocal scientific literature and the Web sites of manufacturers who supply useful accessories.