Mitochondrial outer membrane tail-anchored proteins are a unique class of membrane proteins with unknown targeting mechanism. Using two high-throughput microscopy screens, we demonstrate that the inherent differences in membrane composition between organelle membranes is enough to determine membrane integration specificity in a living cell.

The endoplasmic reticulum (ER) is a large, multifunctional and essential organelle. Despite intense research, the function of more than a third of ER proteins remains unknown even in the well-studied model organism Saccharomyces cerevisiae. One such protein is Spf1, which is a highly conserved, ER localized, putative P-type ATPase. Deletion of SPF1 causes a wide variety of phenotypes including severe ER stress suggesting that this protein is essential for the normal function of the ER. The closest homologue of Spf1 is the vacuolar P-type ATPase Ypk9 that influences Mn2+ homeostasis. However in vitro reconstitution assays with Spf1 have not yielded insight into its transport specificity. Here we took an in vivo approach to detect the direct and indirect effects of deleting SPF1. We found a specific reduction in the luminal concentration of Mn2+ in ∆spf1 cells and an increase following it’s overexpression. In agreement with the observed loss of luminal Mn2+ we could observe concurrent reduction in many Mn2+-related process in the ER lumen. Conversely, cytosolic Mn2+-dependent processes were increased. Together, these data support a role for Spf1p in Mn2+ transport in the cell. We also demonstrate that the human sequence homologue, ATP13A1, is a functionally conserved orthologue. Since ATP13A1 is highly expressed in developing neuronal tissues and in the brain, this should help in the study of Mn2+-dependent neurological disorders.

Commentary 3743Introduction Technological developments in the past years have led to the emergence of high-throughput methods in cell biology (Box 1), where multiple perturbations of a system are automatically repeated in a controlled and identical fashion. These capabilities allow the acquisition of vast amounts of data on a biological system. Evaluating all aspects of such data using computational and mathematical tools can then lead to an unbiased systematic representation of the process studied (Ahn et al., 2006). Technical breakthroughs, often driven by the pharmaceutical industry, have pushed this field forwards and have led to major advances in drug screening (reviewed by Zanella et al., 2010) and numerous discoveries in basic biology.The need for systematic and unbiased approaches has always been at the core of scientific efforts. However, the technology that is required for such efforts often displays an inverse relationship between throughput (speed) and content (biological information). Sydney Brenner referred to this phenomenon by saying that highthroughput experiments are in danger of creating "low-input, high-throughput, no-output biology" (Brenner, 2008). Therefore, it remains a major goal to develop high-throughput science that will give all the advantages of being systematic, accurate, fast and unbiased without giving up the requirement to provide profound and highly informative data.Among the variety of high-throughput approaches available to date (Box 1), one of the methods that holds the promise to bridge the gap between these expectations is high-throughput microscopy, often also referred to as high-content screening (HCS). This is mainly owing to the ability of microscopy methods to focus on single cells at a subcellular resolution, in a time-dependent manner and to measure a large number of parameters in each frame. In this Commentary, we focus on the current frontiers of HCS by presenting the wide range of tools that are utilized and the biological questions that can be tackled using such approaches. We also discuss possible ways to increase content while maintaining throughput at all levels of the screen -from sample design and preparation through to the acquisition and analysis capabilities of the high-content imager system. The power of high-throughput microscopyHigh-throughput microscopy can be employed to address a wide spectrum of biological questions. At the basis of this capability lies the ever-growing variety of labeling methods (discussed below) that allow visualization of cellular architecture and function, as well as developmental or behavioral processes (Fig. 1). In addition, the technological advance of biological tools and microscopic platforms now enables screens to be performed in an array of genetic backgrounds, under different growth conditions and at various time points, as well as allowing the comparison of multiple tissues, cell lines or organisms. Combining the richness of visualization approaches with various experimental strategies creates nearly endless options ...