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.