Hunt, Vicky L. et al. (2019) International Worm Meeting "Loss of the ERGO-1 small RNA pathway in Caenorhabditis inopinata."

Hunt, Vicky L., Murase, Kazunori, Yoshida, Akemi, Kikuchi, Taisei, Tanaka, Ryusei

[International Worm Meeting, 2019]

The ERGO-1 small RNA (sRNA) pathway is best characterised in C. elegans where it is involved in regulating the expression of tandemly duplicated genes and pseudogenes. We are investigating sRNAs in C. inopinata, the closest known relative of C. elegans. Many of the sRNA pathways and their associated sRNAs are conserved between these two species. However, orthologues of the genes coding for the ERGO-1 Argonaute protein and other genes involved in the ERGO-1 pathway have been lost from C. inopinata. This loss is likely to be the result of high levels of transposase activity in the C. inopinata genome. The 26G small interfering RNAs associated with the ERGO-1 pathway are also absent in C. inopinata and the sRNA profiles in these nematodes are similar to C. elegans ergo-1 mutants. To understand the conservation and diversification of the ERGO-1 pathway in nematodes more widely we have identified ERGO-1 pathway orthologues across diverse nematode species. We find that although the ergo-1 Argonaute gene is well conserved amongst nematodes, other genes involved in this pathway are absent from nematodes outside of the Caenorhabiditis clade. We hypothesise that the ERGO-1 pathway found in C. elegans is unique to this clade of nematodes but has been lost in C. inopinata.

Kounosu, Asuka et al. (2021) International Worm Meeting "Chromosome dynamics in sex determination of the parthenogenetic nematode Strongyloides ratti"

Sugimoto, Asako, Maruyama, Haruhiko, Murase, Kazunori, Yoshida, Akemi, Hunt, Vicky, Sun, Simo, Kikuchi, Taisei, Kounosu, Asuka

[International Worm Meeting, 2021]

The genus Strongyloides is unique among nematodes in having alternate free-living and parasitic generations. The parasitic female (PF) inhabits the small intestine of its mammal host and produces clonal offspring by mitotic parthenogenesis. Eggs produced by PF are excreted with the feaces and develop into either infective larvae (iL3) directly or free-living males and females. The free-living adults mate and produce eggs which develop into iL3. It was reported that Strongyloides ratti, a rat parasite, has three chromosomes and one of them is a sex chromosome, which determines their sex by XX/XO system. However, it remains unclear how mitotic parthenogenetic PF produces XX and XO eggs though it is presumed that the male karyotype (XO) is generated by missegregation of the sex chromosome like the C. elegans male generation. In this study we investigated details of the chromosome structure of each developmental stages of S. ratti using the single-worm sequencing technique and the multiplex colored FISH observation. In the single-worm analysis, we expected a half depth of mapping coverage in sex chromosome compared to autosomes in free-living males (XO). However, the sex-chromosome of the male exhibited ~1/3 depth of the autosomes. Furthermore PF and free-living female (XX) showed lower coverage depth of the sex-chromosome and the auto:sex ration varied from 1:0.8 to 1:0.5. Additionally, in germline depleted PF, sex-chromosome showed almost equal coverages as autosomes. These results indicate that chromosome manipulations occurs in the PF germline to produce free-living males and the S. ratti sex determination system is not a simple XX/XO. Multiplex colored FISH analyses, recently developed for C. elegans in-detail chromosome observation, provided visual clues to understanding the dynamics of S. ratti chromosomal structure and the puzzling sex-determination system of Strongyloides.