細胞内カルシウムと睡眠 Intracellular calcium and sleep

細胞内カルシウム濃度を制御するチャネルやポンプが睡眠の長さを決めるということ（睡眠制御遺伝子であること）を提唱した論文が出ました。睡眠の本質があぶり出されつつあると感じます。

Tatsuki F, Sunagawa GA, Shi S, Susaki EA, Yukinaga H, Perrin D, Sumiyama K, Ukai-Tadenuma M, Fujishima H, Ohno R, Tone D, Ode KL, Matsumoto K, Ueda HR. 

Involvement of Ca2+-dependent hyperpolarization in sleep duration in mammals. 

Neuron 2016 AOP  doi: 10.1016/j.neuron.2016.02.032.

プレスリリースはこちら

This paper proposed the idea that intracellular calcium is involved in animal's sleep time, which may be the essential of this biological function.

Press release in English

「平均的ニューロンモデル」を作成し、睡眠時・覚醒時の神経活動の状態をシミュレーションしました。シミュレーターに組み込まれた分子群を仮想ノックアウトしていくと、上記の分子群が睡眠制御遺伝子候補として引っかかってきました。

だいたいこういう遺伝子は「似た者」がいくつかあるのが通常です。そこで、最近話題のCRISPR技術を使って片っ端からファミリー分子のノックアウトマウスを作製し、表現型解析を行いました。

さらに、胎生致死になってしまう遺伝子については、阻害剤の投与で薬理学的に検証。細胞内カルシウムの流入を抑えると、脳全体で神経活動がupregulateされる（つまり寝にくくなってしまう）ことを示しています。

このような大規模な解析を実現するため、近年開発された「個体レベルのシステム生物学」のための技術が活用されました。一世代でノックアウトマウスの作製が可能なTriple-CRISPRシステム [Sunagawa et al. Cell Reports 2016]、マウスを測定チャンバーに入れるだけで睡眠測定が可能なSSS [同上]、全脳スケールで神経細胞の活動をイメージングし解析するCUBIC [Susaki et al. Cell 2014] などです。これらの技術は既存法のスループットを1オーダー以上改善できるものばかりです。

The idea was examined by simulations of an averaged neuron model and following animal sleep analysis of KO mice of 21 genes (!) and a high throughput and non-invasive sleep analysis system. Upregulated neural activities by inhibiton of Ca channel were observed by whole-brain imaging. These technologies has been developed for 'organism-level systems biology' in mammal.

このような規模の研究は、これらの技術がより普及するにつれ、長期的には一般的なものになっていく可能性があります。

ちなみに、「カルシウムを摂れば不眠に効く！？」みたいな感想がちらほらありますが、これはちょっと違う話です ^^;

Reference :

Susaki EA et al. 

Whole-Brain Imaging with Single-Cell Resolution Using Chemical Cocktails and Computational Analysis. 

Cell 157, 726–739, 2014. 

Sunagawa GA et al.

Mammalian Reverse Genetics without Crossing Reveals Nr3a as a Short-Sleeper Gene.

Cell reports 14, 662-677, 2016.

関連記事/related article

PLoS ONE 4(12): e8295, 2010

A Conceptual Mathematical Model of the Dynamic Self-Organisation of Distinct Cellular Organelles

Formation, degradation and renewal of cellular organelles is a dynamic process based on permanent budding, fusion and inter-organelle traffic of vesicles. These processes include many regulatory proteins such as SNAREs, Rabs and coats. Given this complex machinery, a controversially debated issue is the definition of a minimal set of generic mechanisms necessary to enable the self-organization of organelles differing in number, size and chemical composition. We present a conceptual mathematical model of dynamic organelle formation based on interacting vesicles which carry different types of fusogenic proteins (FP) playing the role of characteristic marker proteins. Our simulations (ODEs) show that a de novo formation of non-identical organelles, each accumulating a different type of FP, requires a certain degree of disproportionation of FPs during budding. More importantly however, the fusion kinetics must indispensably exhibit positive cooperativity among these FPs, particularly for the formation of larger organelles. We compared different types of cooperativity: sequential alignment of corresponding FPs on opposite vesicle/organelles during fusion and pre-formation of FP-aggregates (equivalent, e.g., to SNARE clusters) prior to fusion described by Hill kinetics. This showed that the average organelle size in the system is much more sensitive to the disproportionation strength of FPs during budding if the vesicular transport system gets along with a fusion mechanism based on sequential alignments of FPs. Therefore, pre-formation of FP aggregates within the membranes prior to fusion introduce robustness with respect to organelle size. Our findings provide a plausible explanation for the evolution of a relatively large number of molecules to confer specificity on the fusion machinery compared to the relatively small number involved in the budding process. Moreover, we could speculate that a specific cooperativity which may be described by Hill kinetics (aggregates or Rab/SNARE complex formation) is suitable if maturation/identity switching of organelles play a role (bistability).

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Menbrane fusionとbuddingのモデリングの話。