Paper on Pathogenesis of Cardiomyopathy Caused by RBM20 Mutations Published/論文発表

Our paper on pathogenic mechanisms of cardiomyopathy caused by RBM20 mutations analyzed in genome-edited iPS cell-derived cardiomyocytes is finally published. This is literately "finally" published, as this project started when I joined the Conklin lab as a postdoc. At that time, the lab has just started genome editing in human iPS cells. We had a list of mutations that cause cardiomyopathy. I chose RBM20 and a few other genes to start editing them.

The first mutation in RBM20 was reported in 2009, so RBM20 was a relatively new gene back then. RBM20 is a splicing factor, so my thought was that we should be able to analyze global splicing patterns by RNAseq as long as I could introduce the RBM20 mutations. It turned out that I was partially correct and partially wrong. In this paper, we do describe global splicing patterns, which is affected by the RBM20 R636S mutation. However, we also found that the RBM20 mutations are far more harmful than simple splicing dysregulations. The mutant RBM20 forms granules involving various mRNAs in the cytosol, which partially overlaps with P-bodies. More surprisingly, many of the mRNAs associating with the mutant RBM20 are also found to interact with the mutant FUS that causes ALS. Therefore, our study unveils a link between cardiomyopathy and neurodegenerative diseases. Recently, Jay Schneider's group has found the liquid-like material properties of the mutant RBM20, so our findings are consistent with their observations.

Obviously, it took too long to publish this, but I am so happy to see the data are available to anybody. When I started this project almost 10 years ago, introducing single nucleotide substitutions itself was not easy. Therefore, I developed a digital-PCR-based method to substitute nucleotides without selection markers. Then, I was able to find my current position, which was one reason why it took too long.

First, we collected RNAseq data with Nathan Salomonis's group. Then, eCLIP was performed in collaboration with Gene Yeo. Finally, we needed physiological data of our iPS-CMs, and ended up in collaboration with Chuck Murry's group. I remember I met Alessandro at ISSCR (our collaboration started there). I guess that is the power of in-person academic meetings. Then Aidan performed fantastic experiments. I am so lucky to have such excellent collaborators. When I was a postdoc, Amanda and Steven worked so hard to edit the RBM20 in iPS cells and differentiate them into cardiomyocytes. I really thank everybody. Finally, my postdoc is officially over 5 years after physically leaving the lab. Bruce said "not yet" though (really?).


 RBM20の最初の心筋症の原因としての報告は2009年でしたので、当時まだ比較的新しい原因遺伝子でした。RBM20がスプライシング因子であることはわかっていましたので、私がうまく変異の導入さえできれば、RNAseqで少なくともスプライシング様式全体を明らかにすることはできるはずだ、と思って選びました。その予想は半分は正しく、半分は間違っていたと言えます。この論文でも記述している通り、確かにRBM20 R636S変異は心筋細胞のスプライシング様式を、全体的により未熟な状態に変化させていました。しかし、同時に私達は、変異RBM20が多様なmRNAを含む集合体を形成して、その一部が細胞質中のP-bodyと共局在することを見出しました。さらに驚いたことに、その集合体に含まれるmRNAの多くが、ALSの原因となる変異FUSと結合するmRNAと共通だったのです。したがって、私達の発見は心筋症と神経変性疾患の共通点を明らかにするものとなりました。最近、Jay Schneider博士のグループが、変異RBM20が液体様の挙動を示すことを明らかにしており、私達の発見も彼らの発見と整合性のあるものだと思います。


 最初、Nathan Salomonis博士のグループと、RNAseqデータの解析を進めました。続いて、Gene Yeo博士のグループとeCLIPを実施しました。最後に、iPS細胞由来心筋細胞の、より生理的な解析が必要ということになり、Chuck Murry博士のグループと共同研究を行うことができました。AlessandroとISSCRのポスター発表で会ったのを覚えています。それがきっかけでした。こういうのが対面学会の力なんだと思います。で、Aidanが精力的に実験を進めてくれました。素晴らしい共同研究者に恵まれて、非常に幸運でした。私がポスドクをしている間は、AmandaとStevenがゲノム編集とiPS細胞の心筋細胞への分化を強力に推進してくれました。本当にみなさんに感謝です。物理的にConklin研究室を去ってから5年が経って、やっと公式に私のポスドクが終わりました。でもBruceは「まだ」と言ってましたが(ウソでしょ?)。

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