Mechanism of Self-Sterility in a Hermaphroditic Chordate

Yoshito Harada,^1* Yuhei Takagaki,¹ Masahiko Sunagawa,¹ Takako Saito,¹ Lixy Yamada,² Hisaaki Taniguchi,² Eiichi Shoguchi,³ Hitoshi Sawada^1*

Abstract: Hermaphroditic organisms avoid inbreeding by a system of self-incompatibility (SI). A primitive chordate (ascidian) Ciona intestinalis is an example of such an organism, but the molecular mechanism underlying its SI system is not known. Here, we show that the SI system is governed by two gene loci that act cooperatively. Each locus contains a tightly linked pair of polycystin 1–related receptor (s-Themis) and fibrinogen-like ligand (v-Themis) genes, the latter of which is located in the first intron of s-Themis but transcribed in the opposite direction. These genes may encode male- and female-side self-recognition molecules. The SI system of C. intestinalis has a similar framework to that of flowering plants but utilizing different molecules.

¹ Sugashima Marine Biological Laboratory, Graduate School of Science, Nagoya University, Sugashima, Toba 517-0004, Japan.
² Division of Disease Proteomics, Institute for Enzyme Research, the University of Tokushima, 3-15-18 Kuramotocho, Tokushima 770-8503, Japan.
³ Department of Zoology, Graduate School of Science, Kyoto University, Oiwake-cho Kitashirakawa Sakyo-ku, Kyoto 606-8502, Japan.

^* To whom correspondence should be addressed. E-mail: yharada{at}bio.nagoya-u.ac.jp (Y.H.); hsawada{at}bio.nagoya-u.ac.jp (H.S.)

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