Maezawa Takanobu, Ishikawa Masaki, Sekii Kiyono, Nagamatsu Go, Furukawa Ryohei, Kobayashi Kazuya
Advanced Science Course, Department of Integrated Science and Technology, National Institute of Technology, Tsuyama College, 624-1 Numa, Tsuyama, Okayama, 708-8509, Japan.
Faculty of Agriculture and Life Science, Hirosaki University, 3 Bunkyo-cho, Hirosaki, Aomori, 036-8561, Japan.
Zoological Lett. 2021 Mar 20;7(1):4. doi: 10.1186/s40851-021-00173-z.
Many animals switch between asexual and sexual reproduction in nature. We previously established a system for the sexual induction of planarian Dugesia ryukyuensis by feeding asexual planarians with minced sexual planarians. We identified DL-tryptophan (Trp) as one of the sex-inducing substances. DL-Trp can induce ovarian development, the first and essential step of sexual induction. D-Trp must act as a principal bioactive compound in terms of ovarian development, because the ovary-inducing activity of D-Trp was 500 times more potent than that of L-Trp. However, how Trp controls sexual induction is still unknown.
In this study, qRT-PCR analyses suggested that the putative amino acid transporter gene Dr-SLC38A9 is highly expressed in sexual worms, especially in the yolk glands. In situ hybridization analyses showed that Dr-SLC38A9 is expressed in the ovarian primordia of asexual worms and in the mature ovaries, testes, and yolk glands of sexual worms. In addition, Dr-SLC38A9 RNA interference during sexual induction resulted in the suppression of the development of reproductive organs. These results suggest that Dr-SLC38A9 is involved in the development of these organs. Moreover, we demonstrated that the reproductive organ-specific expression of Dr-SLC38A9 is enhanced by the addition of D-Trp.
We propose that D-Trp activates the expression of Dr-SLC38A9 to promote sexual induction in the planarian D. ryukyuensis.
自然界中许多动物会在无性繁殖和有性繁殖之间切换。我们之前建立了一个通过给无性生殖的真涡虫（Dugesia ryukyuensis）喂食切碎的有性生殖真涡虫来诱导其有性生殖的系统。我们鉴定出DL-色氨酸（Trp）是其中一种诱导有性生殖的物质。DL-Trp可诱导卵巢发育，这是有性生殖诱导的第一步且至关重要。就卵巢发育而言，D-Trp必定作为主要的生物活性化合物发挥作用，因为D-Trp诱导卵巢的活性比L-Trp强500倍。然而，Trp如何控制有性生殖诱导仍不清楚。
在本研究中，定量逆转录聚合酶链反应（qRT-PCR）分析表明，推测的氨基酸转运蛋白基因Dr-SLC38A9在有性生殖的蠕虫中高度表达，尤其是在卵黄腺中。原位杂交分析显示，Dr-SLC38A9在无性生殖蠕虫的卵巢原基以及有性生殖蠕虫的成熟卵巢、睾丸和卵黄腺中表达。此外，在有性生殖诱导过程中对Dr-SLC38A9进行RNA干扰导致生殖器官发育受到抑制。这些结果表明Dr-SLC38A9参与了这些器官的发育。而且，我们证明添加D-Trp可增强Dr-SLC38A9在生殖器官中的特异性表达。
我们提出D-Trp激活Dr-SLC38A9的表达以促进真涡虫D. ryukyuensis的有性生殖诱导。
