CRISPR-Cas systems have been used with single-guide RNAs for accurate gene disruption and conversion in multiple biological systems. Here we report the use of the endonuclease Cas9 to target genomic sequences in the C. elegans germline, utilizing single-guide RNAs that are expressed from a U6 small nuclear RNA promoter. Our results demonstrate that targeted, heritable genetic alterations can be achieved in C. elegans, providing a convenient and effective approach for generating loss-of-function mutants.

The novel SUN-domain family of nuclear envelope proteins interacts with various KASH-domain partners to form SUN-domain-dependent 'bridges' across the inner and outer nuclear membranes. These bridges physically connect the nucleus to every major component of the cytoskeleton. SUN-domain proteins have diverse roles in nuclear positioning, centrosome localization, germ-cell development, telomere positioning and apoptosis. By serving both as mechanical adaptors and nuclear envelope receptors, we propose that SUN-domain proteins connect cytoplasmic and nucleoplasmic activities.

We adapted the CRISPR-Cas9 system for template-mediated repair of targeted double-strand breaks via homologous recombination in Caenorhabditis elegans, enabling customized and efficient genome editing. This system can be used to create specific insertions, deletions, and base pair changes in the germline of C. elegans.

At the onset of the first meiotic division, the protein LAB-1 recruits the PP1 phosphatase to cohesion complexes, preventing Aurora B kinase from targeting cohesins for degradation prematurely and thereby ensuring proper progression of meiotic events in C. elegans.

Developmental programs are executed by tightly controlled gene regulatory pathways. Here, we combined the unique sample retrieval capacity afforded by laser capture microscopy with analysis of mRNA abundance by CEL-Seq (cell expression by linear amplification and sequencing) to generate a spatiotemporal gene expression map of the Caenorhabditis elegans syncytial germline from adult hermaphrodites and males. We found that over 6000 genes exhibit spatiotemporally dynamic expression patterns throughout the hermaphrodite germline, with two dominant groups of genes exhibiting reciprocal shifts in expression at late pachytene during meiotic prophase I. We found a strong correlation between restricted spatiotemporal expression and known developmental and cellular processes, indicating that these gene expression changes may be an important driver of germ cell progression. Analysis of the male gonad revealed a shift in gene expression at early pachytene and upregulation of subsets of genes following the meiotic divisions, specifically in early and late spermatids, mostly transcribed from the X chromosome. We observed that while the X chromosome is silenced throughout the first half of the gonad, some genes escape this control and are highly expressed throughout the germline. Although we found a strong correlation between the expression of genes corresponding to CSR-1-interacting 22G-RNAs during germ cell progression, we also found that a large fraction of genes may bypass the need for CSR-1-mediated germline licensing. Taken together, these findings suggest the existence of mechanisms that enable a shift in gene expression during prophase I to promote germ cell progression.

The intimate association between nuclear lamins and chromatin is thought to regulate higher order chromatin organization. Previous studies have mapped a region between the rod domain and the Ig fold in the tail domain of Drosophila melanogaster lamin Dm0, which binds chromatin in vitro via the histone H2A/H2B dimer. This region contains an evolutionarily conserved nuclear localization signal (NLS) KRKR, and a sequence composed of the amino acids TRAT. Here we show that binding of lamin Dm0 to chromatin requires both NLS and TRAT sequences. Substituting either of the threonine residues in the TRAT sequence with negatively charged residues decreases the binding of lamin Dm0 to chromatin, indicating that this binding could be regulated by phosphorylation. Both lamin Dm0 and C. elegans Ce-lamin bind directly to histone H2A in vitro and this binding requires the NLS. The amino and carboxyl tail domains of histone H2A are each essential, but not sufficient, for binding to lamin Dm0; only a polypeptide containing both histone H2A tail domains binds efficiently to lamin Dm0. Taken together, these results suggest that specific residues in lamin Dm0 and histone H2A mediate the attachment of the nuclear lamina to chromosomes in vivo, which could have implications on the understanding of laminopathic diseases.

Asymmetric disassembly of the synaptonemal complex (SC) is crucial for proper meiotic chromosome segregation. However, the signaling mechanisms that directly regulate this process are poorly understood. Here we show that the mammalian Rho GEF homolog, ECT-2, functions through the conserved RAS/ERK MAP kinase signaling pathway in the C. elegans germline to regulate the disassembly of SC proteins. We find that SYP-2, a SC central region component, is a potential target for MPK-1-mediated phosphorylation and that constitutively phosphorylated SYP-2 impairs the disassembly of SC proteins from chromosomal domains referred to as the long arms of the bivalents. Inactivation of MAP kinase at late pachytene is critical for timely disassembly of the SC proteins from the long arms, and is dependent on the crossover (CO) promoting factors ZHP-3/RNF212/Zip3 and COSA-1/CNTD1. We propose that the conserved MAP kinase pathway coordinates CO designation with the disassembly of SC proteins to ensure accurate chromosome segregation.DOI: http://dx.doi.org/10.7554/eLife.12039.001

In Caenorhabditis elegans, the antiapoptotic protein CED-9 is localized at the mitochondria, where it binds the proapoptotic protein CED-4. Induction of apoptosis begins when the proapoptotic protein EGL-1 is expressed and binds CED-9. The binding of EGL-1 to CED-9 releases CED-4 from CED-9 and causes the activation of the caspase CED-3. Upon its release from CED-9, CED-4 rapidly translocates to the nuclear envelope (NE) in a CED-3-independent manner. However, the identity of the NE receptor for CED-4 and its possible role in the execution of apoptosis has remained unknown. Here, we show that the inner nuclear membrane SUN-domain protein matefin͞SUN-1 is the NE receptor for CED-4. Our data demonstrate that matefin͞SUN-1 binds CED-4 and is specifically required for CED-4 translocation and maintenance at the NE. The role of matefin͞SUN-1 in the execution of apoptosis is further suggested by the significant reduction in the number of apoptotic cells in the organism after matefin͞SUN-1 down-regulation by RNAi. The finding that matefin͞SUN-1 is required for the execution of apoptosis adds an important link between cytoplasmic and nuclear apoptotic events.inner nuclear membrane ͉ nuclear lamina ͉ SUN-domain 1 lamin ͉ programmed cell death P rogrammed cell death (apoptosis) is essential for normal development and homeostasis in metazoans (1-3). In the nematode Caenorhabditis elegans, the mitochondria-associated Bcl-2 homologue CED-9 binds the Apaf-1 homologue CED-4. Upon apoptosis initiation, the Bcl-2 homology domain 3-only (BH3-only) protein EGL-1 is expressed and binds CED-9, releasing CED-4, which activates the caspase CED-3 (4). This core apoptotic pathway is conserved in higher eukaryotes (4). Once released, CED-4 translocates from the mitochondria to the nuclear envelope (NE) (5). The NE is composed of inner and outer nuclear membranes that join at the nuclear pore complexes. Underneath the inner nuclear membrane (INM), there is a meshwork of proteins, termed the nuclear lamina, which is composed of lamins and lamin-associated proteins, most of which are integral proteins of the INM (6, 7). The C. elegans INM harbors two LEM-domain proteins (Ce-emerin and Ce-MAN1) (8) and two SUN-domain proteins (UNC-84 and matefin͞ SUN-1) (9, 10). Matefin͞SUN-1 colocalizes with Ce-lamin in vivo and binds Ce-lamin in vitro but does not require Ce-lamin for its NE localization. Matefin͞SUN-1 is present in all embryonic cells until mid͞late embryogenesis and thereafter in germline cells. Matefin͞SUN-1 is essential for embryogenesis and germ-line proliferation and maintenance (10). Matefin͞SUN-1 is also required for centrosome attachment to the nuclear periphery via an interaction with ZYG-12 (11). It was suggested that CED-4 translocation from the mitochondria to the NE plays an important role in apoptosis (5). We report that matefin͞ SUN-1 is specifically required for CED-4 localization at the NE. Furthermore, we show that this localization is probably required for executing apoptosis. Results CED-4 Binds Matefin͞SUN-1 in Vitro.B...