Single cell analysis

Why is it important to study single cells? Scientists have long pondered the purpose of increasingly smaller biological entities within various organisms, with the cell acknowledged to be one of the fundamental building blocks of life. Furthermore, individual cells have discrete molecular, metabolic, and proteomic identities. Analogous to the pieces of a jigsaw puzzle, these distinct cells are interconnected to each other, their biochemical constituents, and their heterogeneous environment. If we are to understand how an organism functions, it follows that we can benefit from knowing how the pieces of the puzzle—the cells—fit together. Efforts to understand the role of a given cell in an organism often require a reductionist approach, either by defining the boundaries of the cell in order to investigate its properties within those borders, or alternatively, by isolating a cell from its environment in preparation for further study. Then, using the information gleaned from the study of the cell, we seek to define its role in the organism as a whole, and to predict the normal function of the whole organism, its developmental changes, and/or its pathological conditions. Single cell analysis is a key to the success of biological reductionism. Despite the major investigative challenges that these studies can present, researchers continue to define innovative analytical strategies and emerging technologies that are allowing us to examine, on an ever more diminutive scale, entire organs, cellular clusters, single cells, and even subcellular compartments. This Special Issue celebrates those who have undertaken the analytical challenge inherent in studying cells at the single and subcellular level. Contributions include Trends articles, which describe new advances in measurement technology and new application areas related to single cell analysis, several timely Reviews, and a collection of Original Papers presenting a range of studies in the area of single cell and subcellular analysis. Highlighting state-of-the-art microfluidics, microfabrication, and cell sorting are the Trends articles on sampling and cellular manipulations, including the works of Chiu, Allbritton, Culbertson, and Palcic. Once the cell is sampled, how can its contents be analyzed? Ewing and coworkers have written a Review on the application of capillary electrophoresis to cellular analysis, and Hua Zhang discusses the emergence of highly selective/sensitive immunocapillary electrophoretic methods. Mass spectrometric-based approaches are also represented by the exciting work of Ka Wan Li on the proteomics of the synapse, and by the use of MS for peptide discovery in arthropods by Lingjun Li. Due to the importance of monitoring intracellular dynamic processes, innovative microscopic developments and applications are also included in this issue. Eberwine and his group describe their exciting research on RNA transport and localization in the dendrites of neurons using molecular approaches, while individual studies by Kubitscheck and Knemeyer describe innovative techniques for tracking and measuring single molecules within cells. Interestingly, even though most think of single cell measurements primarily in relationship Anal Bioanal Chem (2007) 387:1–2 DOI 10.1007/s00216-006-0921-4