Genome-wide analysis of gene function is essential for the post-genome era, and development of efficient and economical technology suitable for it has been in demand. Here we report a large-scale inactivation of the expressed genes in the nematode Caenorhabditis elegans. For this purpose, we have established a high-throughput "RNAi-by-soaking" methodology by modifying the conventional RNAi method [1, 2]. A set of tag-sequenced, nonredundant cDNAs corresponding to approximately 10,000 genes [3] (representing half of the predicted genes [4]) was used for the systematic RNAi analysis. We have processed approximately 2500 genes to date. In development, 27% of them showed detectable phenotypes, such as embryonic lethality, post-embryonic lethality, sterility, and morphological abnormality. Of these, we analyzed the phenotypes of F1 sterility in detail, and we have identified 24 genes that might play important roles in germline development. Combined with the ongoing analysis of expression patterns of these cDNAs [3, 5], the functional information obtained in this work will provide a starting point for the further analysis of each gene. Another finding from this screening is that the incidence of essential genes is significantly lower in the X chromosome than in the autosomes.

Schizosaccharomyces pombe stell encodes a member of the family of HMG-box proteins. Its transcript is induced in response to nitrogen starvation and a concomitant decrease of the intracellular cAMP level. Expression of stell is essential for induction of sexual development, and its ectopic expression stimulates uncontrolled mating and sporulation. Stel 1 protein regulates positively transcription of the following genes required for sexual development: the mating type genes, matP and matM, and the mei2 gene, which is essential for commitment to meiosis. Stel 1 protein synthesized in vitro binds specifically to a DNA fragment carrying a 10-base motif TTCTTTGTTY that is an essential c/s-acting element for the induction of mei2 and is commonly seen in the upstream regions of the genes inducible by nitrogen starvation. These observations strongly suggest that Stel 1 serves as a key transcription factor for sexual development.

Chromosome segregation requires stable bipolar attachments of spindle microtubules to kinetochores. The dynein/dynactin motor complex localizes transiently to kinetochores and is implicated in chromosome segregation, but its role remains poorly understood. Here, we use the Caenorhabditis elegans embryo to investigate the function of kinetochore dynein by analyzing the Rod/Zwilch/Zw10 (RZZ) complex and the associated coiled-coil protein SPDL-1. Both components are essential for Mad2 targeting to kinetochores and spindle checkpoint activation. RZZ complex inhibition, which abolishes both SPDL-1 and dynein/dynactin targeting to kinetochores, slows but does not prevent the formation of load-bearing kinetochore-microtubule attachments and reduces the fidelity of chromosome segregation. Surprisingly, inhibition of SPDL-1, which abolishes dynein/dynactin targeting to kinetochores without perturbing RZZ complex localization, prevents the formation of load-bearing attachments during most of prometaphase and results in extensive chromosome missegregation. Coinhibition of SPDL-1 along with the RZZ complex reduces the phenotypic severity to that observed following RZZ complex inhibition alone. We propose that the RZZ complex can inhibit the formation of load-bearing attachments and that this activity of the RZZ complex is normally controlled by dynein/dynactin localized via SPDL-1. This mechanism could coordinate the hand-off from initial weak dynein-mediated lateral attachments, which help orient kinetochores and enhance their ability to capture microtubules, to strong end-coupled attachments that drive chromosome segregation.[Keywords: Centromere; aneuploidy; mitosis; kinetochore; microtubule; spindle; chromosome] Supplemental material is available at http://www.genesdev.org. In higher eukaryotes, kinetochores are built on the centromere region of chromosomes to connect to the microtubules of the nascent mitotic spindle after nuclear envelope breakdown (NEBD). To avoid chromosome loss, kinetochores must be efficient at capturing microtubules emanating from the two spindle poles and at converting initial transient contacts into stable end-coupled attachments capable of resisting the forces that drive chromosome alignment (Nicklas 1988). A safeguard is provided by the mitotic spindle checkpoint, which delays cell cycle progression by producing a diffusible inhibitor at kinetochores that have not yet captured microtubules (Musacchio and Salmon 2007). Stable end-on attachments shut off production of the inhibitory signal, allowing the cell to exit mitosis.The core microtubule attachment site at the kinetochores is formed by a set of conserved interacting proteins, collectively named the KMN network after its