Autophagy is a tightly regulated intracellular bulk degradation/recycling system that has fundamental roles in cellular homeostasis. Autophagy is initiated by isolation membranes, which form and elongate as they engulf portions of the cytoplasm and organelles. Eventually isolation membranes close to form double membrane-bound autophagosomes and fuse with lysosomes to degrade their contents. The physiological role of autophagy has been determined since its discovery, but the origin of autophagosomal membranes has remained unclear. At present, there is much controversy about the organelle from which the membranes originate--the endoplasmic reticulum (ER), mitochondria and plasma membrane. Here we show that autophagosomes form at the ER-mitochondria contact site in mammalian cells. Imaging data reveal that the pre-autophagosome/autophagosome marker ATG14 (also known as ATG14L) relocalizes to the ER-mitochondria contact site after starvation, and the autophagosome-formation marker ATG5 also localizes at the site until formation is complete. Subcellular fractionation showed that ATG14 co-fractionates in the mitochondria-associated ER membrane fraction under starvation conditions. Disruption of the ER-mitochondria contact site prevents the formation of ATG14 puncta. The ER-resident SNARE protein syntaxin 17 (STX17) binds ATG14 and recruits it to the ER-mitochondria contact site. These results provide new insight into organelle biogenesis by demonstrating that the ER-mitochondria contact site is important in autophagosome formation.

Degenerative disorders of motor neurons include a range of progressive fatal diseases such as amyotrophic lateral sclerosis (ALS), spinal-bulbar muscular atrophy (SBMA), and spinal muscular atrophy (SMA). Although the causative genetic alterations are known for some cases, the molecular basis of many SMA and SBMA-like syndromes and most ALS cases is unknown. Here we show that missense point mutations in the cytoplasmic dynein heavy chain result in progressive motor neuron degeneration in heterozygous mice, and in homozygotes this is accompanied by the formation of Lewy-like inclusion bodies, thus resembling key features of human pathology. These mutations exclusively perturb neuron-specific functions of dynein.

Cloning of the entire set of an organism's protein-coding open reading frames (ORFs), or 'ORFeome', is a means of connecting the genome to downstream 'omics' applications. Here we report a proteome-scale study of the fission yeast Schizosaccharomyces pombe based on cloning of the ORFeome. Taking advantage of a recombination-based cloning system, we obtained 4,910 ORFs in a form that is readily usable in various analyses. First, we evaluated ORF prediction in the fission yeast genome project by expressing each ORF tagged at the 3' terminus. Next, we determined the localization of 4,431 proteins, corresponding to approximately 90% of the fission yeast proteome, by tagging each ORF with the yellow fluorescent protein. Furthermore, using leptomycin B, an inhibitor of the nuclear export protein Crm1, we identified 285 proteins whose localization is regulated by Crm1.

Much remains unknown about the molecular regulation of meiosis. Here we show that meiosis-specific transcripts are selectively removed if expressed during vegetative growth in fission yeast. These messenger RNAs contain a cis-acting region--which we call the DSR--that confers this removal via binding to a YTH-family protein Mmi1. Loss of Mmi1 function severely impairs cell growth owing to the untimely expression of meiotic transcripts. Microarray analysis reveals that at least a dozen such meiosis-specific transcripts are eliminated by the DSR-Mmi1 system. Mmi1 remains in the form of multiple nuclear foci during vegetative growth. At meiotic prophase these foci precipitate to a single focus, which coincides with the dot formed by the master meiosis-regulator Mei2. A meiotic arrest due to the loss of the Mei2 dot is released by a reduction in Mmi1 activity. We propose that Mei2 turns off the DSR-Mmi1 system by sequestering Mmi1 to the dot and thereby secures stable expression of meiosis-specific transcripts.

The movement of chromosomes that precedes meiosis was observed in living cells of fission yeast by fluorescence microscopy. Further analysis by in situ hybridization revealed that the telomeres remain clustered at the leading end of premeiotic chromosome movement, unlike mitotic chromosome movement in which the centromere leads. Once meiotic chromosome segregation starts, however, centromeres resume the leading position in chromosome movement, as they do in mitosis. Although the movement of the telomere first has not been observed before, the clustering of telomeres is reminiscent of the bouquet structure of meiotic-prophase chromosomes observed in higher eukaryotes, which suggests that telomeres perform specific functions required for premeiotic chromosomal events generally in eukaryotes.

The mouse Nedd5 gene encodes a 41.5-kD GTPase similar to the Saccharomyces and Drosophila septins essential for cytokinesis. Nedd5 accumulates near the contractile ring from anaphase through telophase, and finally condenses into the midbody. Microinjection of anti-Nedd5 antibody interferes with cytokinesis, giving rise to binucleated cells. In interphase and postmitotic cells, Nedd5 localizes to fibrous or granular structures depending on the growth state of the cell. The Nedd5-containing fibers are disrupted by microinjection of GTP~,S and by Nedd5 mutants lacking GTP-binding activity, implying that GTP hydrolysis is required for its assembly. The Nedd5-containing fibers also appear to physically contact actin bundles and focal adhesion complexes and are disrupted by cytochalasin D, C3 exoenzyme, and serum starvation, suggesting a functional interaction with the actin-based cytoskeletal systems in interphase cells.

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In many organisms, meiotic chromosomes are bundled at their telomeres to form a "bouquet" arrangement. The bouquet formation plays an important role in homologous chromosome pairing and therefore progression of meiosis. As meiotic telomere clustering occurs in response to mating pheromone signaling in fission yeast, we looked for factors essential for bouquet formation among genes induced under mating pheromone signaling. This genome-wide search identified two proteins, Bqt1 and Bqt2, that connect telomeres to the spindle-pole body (SPB; the centrosome equivalent in fungi). Neither Bqt1 nor Bqt2 alone functions as a connector, but together the two proteins form a bridge between Rap1 (a telomere protein) and Sad1 (an SPB protein). Significantly, when both Bqt1 and Bqt2 are ectopically expressed in mitotic cells, they also form a bridge between Rap1 and Sad1. Thus, a complex including Bqt1 and Bqt2 is essential for connecting telomeres to the SPB.