Maternal factor-mediated epigenetic gene silencing in the ascidian Ciona intestinalis
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Epigenetic regulation of genes plays a critical role in achieving proper gene expression during development, and it has been reported that epigenetic modifications are associated with transposon silencing in many organisms. Here, we report a type of epigenetic gene silencing, maternal gfp/gene silencing (MGS), in the basal chordate Ciona intestinalis. A transgenic line of Ciona, Tg[MiTFr3dTPOG]45 (abbreviated as Tg45), which was created with the Minos transposon, has a tandemly arrayed insertion of gfp in the promoter region of Ci-CesA. Progeny of Tg45 showed a reduced level of GFP expression when eggs of Tg45 were fertilized with sperm of other gfp transgenic lines. Although the genotype is the same, animals developed from Tg45 sperm and the eggs of other transgenic lines did not exhibit this phenomenon, suggesting the involvement of a maternal cytoplasmic factor that influences GFP expression. The silencing starts during oogenesis and continues after fertilization without any tissue specificity. We found that post-transcriptional degradation of the gfp mRNA is involved in MGS.
KeywordsEpigenetics Minos Ci-CesA Transcription
The authors would like to thank Kazuko Hirayama, Yasuo Kasuga, Yasutaka Tsuchiya, Toshihiko Sato, Hideo Shinagawa, Yoshiko Harada and Hiromi Takahashi for their kind cooperation in our study. We thank all members of the Maizuru Fishery Research Station of Kyoto University, the International Coast Research Center of the Ocean Research Institute of the University of Tokyo and the Education and Research Center of Marine Bioresources of Tohoku University for the collection of Ciona adults. We also thank Shigeki Fujiwara and his laboratory members for useful discussion and for providing wild-type Ciona. We are grateful to William Smith, Charalambos Savakis, Brad Davidson, Maki Shirae-Kurabayashi, Hiroki Takahashi, Takahito Nishikata, Naohito Takatori and Hiroki Nishida for kindly providing Cs-CesA cDNA, Minos, pMiCiTnIG, pMiCiEf1aG, pCi-Bra promoter/pEGFP-N1/CMV(−), pCi-Nut promoter/pEGFP-N1/CMV(−) and pBS-HTB. We are also grateful to Adrian Bird for his helpful discussions and for generously allowing the use of his faculty. This study was supported by Grants-in-Aid for Scientific Research from JSPS and MEXT to Nori Satoh (17207013) and Yasunori Sasakura (18770193 and 20681019). Yasunori Sasakura was also supported by the NIG Cooperative Research Program (2007-B01, 2008-B02 and 2009-A18) and by a Narishige Zoological Science Award. This study was further supported by grants from the National Bioresource Project.
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