A comprehensive comparison of sex-inducing activity in asexual worms of the planarian Dugesia ryukyuensis: The crucial sex-inducing substance appears to be present in yolk glands in Tricladida

Haruka Nakagawa, Kiyono Sekii, Takanobu Maezawa, Makoto Kitamura, Soichiro Miyashita, Marina Abukawa, Midori Matsumoto, Kazuya Kobayashi

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2 Citations (Scopus)


Background: Turbellarian species can post-embryonically produce germ line cells from pluripotent stem cells called neoblasts, which enables some of them to switch between an asexual and a sexual state in response to environmental changes. Certain low-molecular-weight compounds contained in sexually mature animals act as sex-inducing substances that trigger post-embryonic germ cell development in asexual worms of the freshwater planarian Dugesia ryukyuensis (Tricladida). These sex-inducing substances may provide clues to the molecular mechanism of this reproductive switch. However, limited information about these sex-inducing substances is available. Results: Our assay system based on feeding sex-inducing substances to asexual worms of D. ryukyuensis is useful for evaluating sex-inducing activity. We used the freshwater planarians D. ryukyuensis and Bdellocephala brunnea (Tricladida), land planarian Bipalium nobile (Tricladida), and marine flatworm Thysanozoon brocchii (Polycladida) as sources of the sex-inducing substances. Using an assay system, we showed that the three Tricladida species had sufficient sex-inducing activity to fully induce hermaphroditic reproductive organs in asexual worms of D. ryukyuensis. However, the sex-inducing activity of T. brocchii was sufficient only to induce a pair of ovaries. We found that yolk glands, which are found in Tricladida but not Polycladida, may contain the sex-inducing substance that can fully sexualize asexual worms of D. ryukyuensis. Conclusions: Our results suggest that within Tricladida, there are one or more common compounds or functional analogs capable of fully sexualizing asexual worms of D. ryukyuensis; namely, the crucial sex-inducing substance (hydrophilic and heat-stable, but not a peptide) produced in yolk glands.

Original languageEnglish
Article number14
JournalZoological Letters
Issue number1
Publication statusPublished - 2018 Jun 12



  • Asexual reproduction
  • Dugesia ryukyuensis
  • Planarian
  • Polyclad
  • Sex-inducing substance
  • Sexual induction
  • Sexual reproduction
  • Triclad
  • Turbellaria

ASJC Scopus subject areas

  • Animal Science and Zoology

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