New research has found that the speed at which the calcium concentration in the cell changes controls the swimming behavior of sperm.
精子進(jìn)入體內(nèi)，只有一個(gè)目的,，就是尋找到卵細(xì)胞,，然而與此同時(shí)，卵細(xì)胞可以釋放誘導(dǎo)劑來(lái)吸引精子靠近,，鈣離子濃度可以決定精子尾巴的移動(dòng)方式,，近日，來(lái)自哥廷根大學(xué)等處的研究人員發(fā)現(xiàn),，當(dāng)鈣離子濃度發(fā)生改變以后,，精子可以立即作出反應(yīng)，而精子對(duì)鈣離子的濃度本身并沒(méi)有反應(yīng),，有可能是精子可以進(jìn)行精準(zhǔn)的計(jì)算,，計(jì)算出鈣離子濃度的變化，以便在高濃度鈣離子的時(shí)候進(jìn)行活動(dòng),。這項(xiàng)研究成果刊登在了國(guó)際著名雜志Journal of Cell Biology上,。
精子游動(dòng)的路徑是根據(jù)卵子釋放引誘劑的方式來(lái)進(jìn)行的，尤其是海生動(dòng)物精子的游動(dòng)途徑是依據(jù)化學(xué)物質(zhì)濃度梯度來(lái)進(jìn)行的,，游動(dòng)的模式受到精子尾部的鈣離子濃度的控制,，在高濃度鈣離子的條件下，精子可以以一種非對(duì)稱的,，像鞭子一樣扭動(dòng)的方式來(lái)移動(dòng),，這種運(yùn)動(dòng)途徑是扭曲的；而在低鈣離子濃度條件下,，精子的尾巴將會(huì)進(jìn)行有規(guī)律的拍打,，并且游動(dòng)的路徑呈直線，這種鈣離子濃度高低更替的方式可以使得精子以螺旋形的方式前進(jìn),，然后通過(guò)在實(shí)驗(yàn)室研究自由游動(dòng)的精子發(fā)現(xiàn),，精子這種傳統(tǒng)的游動(dòng)模式并不是固定不變的,。
研究者Luis Alvarez用精巧的頻閃鐳射照明技術(shù)（ingenious stroboscopic laser illumination）可以精確地追蹤精子的運(yùn)動(dòng)軌跡，而且還可以同時(shí)測(cè)定精子周?chē)h(huán)境中鈣離子濃度的變化情況,，研究結(jié)果表明,，精子尾巴僅僅對(duì)鈣離子濃度的時(shí)間導(dǎo)數(shù)有反應(yīng)，而對(duì)于鈣離子濃度并無(wú)明顯關(guān)系,，結(jié)果進(jìn)一步表明,，精子可以自己進(jìn)行計(jì)算，目前這種機(jī)制尚不清楚,，研究人員懷疑,，精子有可能通過(guò)自身的兩個(gè)蛋白結(jié)合到鈣離子上從而形成一種化學(xué)衍生物。
然而精子為什么會(huì)進(jìn)行如此復(fù)雜的計(jì)算,？就好比我們?cè)诟咧袝r(shí)候碰見(jiàn)的復(fù)雜計(jì)算一樣,。精子身上誘導(dǎo)物和鈣離子濃度非常高，和卵子的基本接近,，然后精子可以利用精妙的“數(shù)學(xué)計(jì)算”在高濃度鈣離子存在的情況下做出及時(shí)反應(yīng),。
除了鈣離子外，機(jī)體中其它的信使物質(zhì)也可以控制細(xì)胞的功能發(fā)揮,，當(dāng)然完全有可能,，細(xì)胞也可以通過(guò)進(jìn)行復(fù)雜的化學(xué)濃度計(jì)算來(lái)介導(dǎo)其它信使物質(zhì)之間的信號(hào)通路，研究者將會(huì)對(duì)這個(gè)問(wèn)題進(jìn)一步進(jìn)行研究,。（生物谷：T.Shen編譯）
doi:10.1083/jcb.201106096
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The rate of change in Ca2+ concentration controls sperm chemotaxis
Luis Alvarez1, Luru Dai2, Benjamin M. Friedrich3, Nachiket D. Kashikar1, Ingo Gregor4, René Pascal1, and U. Benjamin Kaupp1
During chemotaxis and phototaxis, sperm, algae, marine zooplankton, and other microswimmers move on helical paths or drifting circles by rhythmically bending cell protrusions called motile cilia or flagella. Sperm of marine invertebrates navigate in a chemoattractant gradient by adjusting the flagellar waveform and, thereby, the swimming path. The waveform is periodically modulated by Ca2+ oscillations. How Ca2+ signals elicit steering responses and shape the path is unknown. We unveil the signal transfer between the changes in intracellular Ca2+ concentration ([Ca2+]i) and path curvature (κ). We show that κ is modulated by the time derivative d[Ca2+]i/dt rather than the absolute [Ca2+]i. Furthermore, simulation of swimming paths using various Ca2+ waveforms reproduces the wealth of swimming paths observed for sperm of marine invertebrates. We propose a cellular mechanism for a chemical differentiator that computes a time derivative. The cytoskeleton of cilia, the axoneme, is highly conserved. Thus, motile ciliated cells in general might use a similar cellular computation to translate changes of [Ca2+]i into motion.
