A complex containing the Sm protein CAR-1 and the RNA helicase CGH-1 is required for embryonic cytokinesis in Caenorhabditis elegans

Abstract

Cytokinesis completes cell division and partitions the contents of one cell to the two daughter cells. Here we characterize CAR-1, a predicted RNA binding protein that is implicated in cytokinesis. CAR-1 localizes to germline-specific RNA-containing particles and copurifies with the essential RNA helicase, CGH-1, in an RNA-dependent fashion. The atypical Sm domain of CAR-1, which directly binds RNA, is dispensable for CAR-1 localization, but is critical for its function. Inhibition of CAR-1 by RNA-mediated depletion or mutation results in a specific defect in embryonic cytokinesis. This cytokinesis failure likely results from an anaphase spindle defect in which interzonal microtubule bundles that recruit Aurora B kinase and the kinesin, ZEN-4, fail to form between the separating chromosomes. Depletion of CGH-1 results in sterility, but partially depleted worms produce embryos that exhibit the CAR-1–depletion phenotype. Cumulatively, our results suggest that CAR-1 functions with CGH-1 to regulate a specific set of maternally loaded RNAs that is required for anaphase spindle structure and cytokinesis.

RAP55, a Cytoplasmic mRNP Component, Represses Translation in Xenopus Oocytes

“…In Drosophila oocytes and nurse cells, Tral is associated with a subset of endoplasmic reticulum exit sites and is required for the proper secretion of proteins such as Gurken and Yolkless (58). Importantly, interactions between the RAP55 homologues, the Xp54 homologues, and the Y-box proteins are conserved in these organisms, indicating that RAP55 and its homologues constitute core components of mRNPs together with the Xp54 homologues and the Y-box proteins and execute various functions (49,50,56,58). In previous studies with somatic cells such as rabbit reticulocytes or mouse L cells, core components of cytoplasmic mRNPs consisted of the Y-box proteins and the poly(A)-binding protein (59,60).…”

“…Recently, diverse functions have been reported for C. elegans and Drosophila homologues of RAP55, CAR-1, and Trailer hitch (Tral), respectively (56). In C. elegans CAR-1 is required for embryonic cytokinesis, regulation of physiological germ line apoptosis, and organization of the endoplasmic reticulum (49,50,57). Depletion of CAR-1 leads to a defect in cytokinesis during early embryogenesis resulting from an anaphase spindle defect (57).…”

“…In C. elegans during embryonic division, CAR-1 localizes to P granules, which are cytoplasmic particles enriched in the germ line precursors and contain poly(A) ϩ RNAs (49,50). In Xenopus, germ granules, which are also cytoplasmic granules in oocytes and eggs, are essential for germ line development (61).…”

Manipulation of Karyotype inCaenorhabditis elegansReveals Multiple Inputs Driving Pairwise Chromosome Synapsis During Meiosis

“…These include a strain expressing GFP::COSA-1, which marks the sites of crossover recombination events in late pachytene and diplotene meiocytes (Yokoo et al 2012) (Figure 3E), in combination with mCherry::histone H2B and a plasma membrane marker (Audhya et al 2005;McNally et al 2006); a strain carrying the mnT12(IV:X) fusion chromosome in combination with the GFP::COSA-1-expressing transgene (Yokoo et al 2012) ( Figure 3F); and a strain heterozygous for the mIn1 chromosomal inversion and recessive morphological markers (see below). Thus, our strategy provides a reliable and generalizable means to generate tetraploid strains with complex genotypes that would have been nearly impossible to construct by other methods.…”

Germ Cell Apoptosis and DNA Damage Responses

“…However, inactivation of these and other genes by mutation or RNAi leads to additional germline defects, such as an extended pachytene zone, reduced progeny, full or partial sterility, or a generally misshapen germline (Audhya et al 2005 ;Green et al 2011 ;Squirrell et al 2006 ) . Thus excessive apoptosis might be a secondary consequence of pleiotropic germ cell defects.…”