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    Nearly Complete Genome Assembly of the Pinewood Nematode Bursaphelenchus xylophilus Strain Ka4C1
    (Amer Soc Microbiology, 2020) Dayi, Mehmet; Sun, Simo; Maeda, Yasunobu; Tanaka, Ryusei; Yoshida, Akemi; Tsai, Isheng Jason; Kikuchi, Taisei
    Bursaphelenchus xylophilus has been destroying pine forests in East Asia and western Europe. Here, we report its nearly complete genomic sequence containing five similar to 12-Mb scaffolds and one similar to 15-Mb scaffold representing six chromosomes. Large repeat regions that were previously unidentified are now reasonably integrated, particularly in the similar to 15-Mb scaffold.
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    Possible stochastic sex determination in Bursaphelenchus nematodes
    (Nature Portfolio, 2022) Shinya, Ryoji; Sun, Simo; Dayı, Mehmet; Tsai, Isheng Jason; Miyama, Atsushi; Chen, Anthony Fu; Hasegawa, Koichi
    Sex determination mechanisms evolve surprisingly rapidly, yet little is known in the large nematode phylum other than for Caenorhabditis elegans, which relies on chromosomal XX-XO sex determination and a dosage compensation mechanism. Here we analyze by sex-specific genome sequencing and genetic analysis sex determination in two fungal feeding/plant-parasitic Bursaphelenchus nematodes and find that their sex differentiation is more likely triggered by random, epigenetic regulation than by more well-known mechanisms of chromosomal or environmental sex determination. There is no detectable difference in male and female chromosomes, nor any linkage to sexual phenotype. Moreover, the protein sets of these nematodes lack genes involved in X chromosome dosage counting or compensation. By contrast, our genetic screen for sex differentiation mutants identifies a Bursaphelenchus ortholog of tra-1, the major output of the C. elegans sex determination cascade. Nematode sex determination pathways might have evolved by bottom-up accretion from the most downstream regulator, tra-1. In most species, sex is determined by genetic or environmental factors. Here, the authors present evidence that sex determination in Bursaphelenchus nematodes is instead likely to be regulated by a random, epigenetic mechanism.