Zhang, Liangyu et al. (2017) International Worm Meeting "A compartmentalized signaling network mediates crossover assurance and crossover interference in meiosis."

Kohler, Simone, Bohn, Regina, Dernburg, Abby, Zhang, Liangyu

[International Worm Meeting, 2017]

Meiotic crossover control is a central mystery of sexual reproduction. During meiosis, crossover between homologous chromosomes is tightly regulated to ensure proper segregation. Each chromosome pair typically undergoes at least one crossover (crossover assurance) but these exchanges are also strictly limited in number and widely spaced along chromosomes (crossover interference). This has implied the existence of chromosome-wide signals that regulate crossovers, but their molecular basis remains mysterious. Early this year, we reported that the synaptonemal complex, a polymer that assembles between homologous chromosomes during meiosis, forms a phase-separated, liquid crystalline compartment. We suggested that this could explain how the synaptonemal complex might act as a conduit for signals that mediate crossover control along paired chromosomes. We recently characterized a family of four RING finger E3 ligases in C. elegans. We found that these proteins act as two heterodimers within the synaptonemal complex, creating a self-extinguishing circuit that controls crossover designation and maturation. These proteins also act at the top of a hierarchical chromosome remodeling process that enables crossovers to direct stepwise segregation. Work in the other organisms indicates that analogous mechanisms mediate crossover control in most eukaryotes.

Martin, Olivier et al. (2021) International Worm Meeting "A faster and more efficient RNASeq protocol supports new approaches for studying gene regulation and tissue composition in C. elegans"

Stroustrup, Nicholas, Martin, Olivier, Eder, Matthias

[International Worm Meeting, 2021]

Individuals with identical genotypes often show high phenotypic variability. To better characterize inter-individual differences in aging, we further optimized the low-input Smart-seq2 RNASeq strategy (Picelli et al., 2014; Serra et al., 2018) to support routine collection of high-quality C. elegans transcriptomes. Compared to conventional techniques that require thousands of individuals as input material, we have validated our method to show that it can produce robust results from single individuals, and scales up to pools of thirty worms at which point it replaces existing bulk methods. This combination of single and pooled RNASeq provides a quantitative means for studying variation in gene regulation and tissue composition between individuals and across populations. Looking to increase throughput and reduce cost over existing approaches, we identified an eccentricity of the Smart-seq2 template-switching polymerase that in C. elegans leads to an aberrant amplification of specific ribosomal RNAs independent of the poly-dT primers used during reverse transcription. More generally, we find that Smart-seq2 template-switching oligomers bind non-specifically to multiple non-coding RNAs. We solve this problem by combining biotin-labeled primers with an additional bead purification step after reverse transcription. This procedure excludes all non-coding RNAs and increases our effective sequencing depth by 4.5 fold, providing pooled or single-worm transcriptomes at dramatically lower cost. We demonstrate the usefulness of this new method to identify novel downstream targets of the daf-2 insulin/IGF receptor. References Picelli, Simone, et al. "Full-length RNA-seq from single cells using Smart-seq2." Nature protocols 9.1 (2014): 171-181. Serra, Lorrayne, et al. "Adapting the Smart-seq2 protocol for robust single worm RNA-seq." Bio-protocol 8.4 (2018).

Brunschwig K et al. (1998) European Worm Meeting "The labial-like Hox gene ceh-13 controls anterior morphogenesis in the C. elegans embryo"

Brunschwig K, Tobler H, Mueller F, Schnabel R, Wittmann C

[European Worm Meeting, 1998]

lin-39, ceh-13, mab-5 and egl-5 belong to the C. elegans Hox cluster. Mutational analyses of three of these genes, namely lin-39, mab-5 and egl-5 have demonstrated that they specify cell fate along the antero-posterior axis of the nematode during post-embryonic development (1). To study the function of the labial-like Hox gene ceh-13, we isolated a ceh-13 loss-of-function allele, sw1, by transposon-mediated mutagenesis (2) that lacks the homeobox which encodes a DNA-binding domain (3). The deletion of the homeobox as well as the absence of a shorter transcript on Northern blot from total RNA of heterozygous ceh-13 (sw1) animals suggest that ceh-13 (sw1) is a null allele. Homozygous ceh-13 (sw1) animals exhibit a Vab (variable abnormal morphology) phenotype characterized by a recessive, incompletely penetrant, zygotic lethal phenotype. Homozygotes arrest during embryogenesis or at early larval stages. ceh-13 mutants fail to elongate properly, resulting in most cases in very short animals with anterior protuberances and in addition show strong defects in movement. To gain further insight into the role of ceh-13 during embryonic development, we lineaged ceh-13 mutants using a 4D microscope and analysis software. We did not detect any lineage transformation up to the bean stage, but observed that anterior hypodermal and mesodermal cells were mispositioned and that a few different ectodermal (neuronal and hypodermal) cells lost contact with the rest of the embryo. To confirm our lineage analyses, we made use of a variety of tissue-specific markers. All markers assayed in ceh-13 embryos revealed that cells, including muscle, neuronal and hypodermal cells, fully differentiate. However, anterior hypodermal and mesodermal cells are mispatterned at the elongation stage. Interestingly, at this stage, CEH-13 is present in the anterior hypodermal cells as well as in anterior dorsal muscle cells and in cells of the prospective ventral nerve cord (for further details see the abstract of Reto Kohler et al.). Similarly to the activity of vab-7 (4) and nob-1 (5) in the posterior, ceh-13 seems to acts in the anterior part of the C. elegans elongating embryo as a patterning gene. (1) Salser and Kenyon, 1994, TIG 10: 159-164. (2) Zwaal et al.,PNAS, 1993, PNAS 90: 7431-7435. (3) Gehring et al., 1990, TIG 6: 323-329. (4) Ahringer, 1996, Genes & Development 10: 1120-1130. (5) Van Auken et al, 1998, WBG 15(2): 28.