A Sperms Tale: Calcium gets the Turn On! Wonder how a sperm finds the egg?

A Sperms Tale: Calcium gets the Turn On! Wonder how a sperm finds the egg?

The original guided missile: A chemoattractant released by the egg binds to its receptor on the sperm surface, and sets off a signaling cascade. First, cyclic GMP is made, which opens a set of K+ channels. These alter the voltage across the membrane to make it more negatively charged inside, which in turn opens voltage sensing Ca2+ channels. Calcium ions rush in, and direct the movement of the sperm by controlling the beating of tail (flagellum).

As the sperm turns: To understand how calcium controls the sperm, researchers used a “caged” form of cGMP that could be light-activated,and a fluorescent dye to measure Ca2+ ions. Then they tracked sperm movement under a fluorescence microscope. The left panel tracks a single sperm (thick lines drawn over it), first in slow motion and then in real time. In both graphs on the right, the pink lines track the path, with turns shown as peaks. The sperm alternately makes straight runs and turns. In the upper graph, calcium levels (F) are tracked in green. Although, there is some general overlap with sperm movement, the two are not perfectly correlated. But in the lower graph, the rate of change of calcium (dF/dT, mathematically, the time derivative) matches the turns perfectly. In other words, sperms respond to change, not absolute levels of signal. The fastness of the calcium surge controls the sharpness of the turn! The path of the subsequent run depends on the steepness of the decline .

The tail that wags the dog: How does the sperm “compute” the time derivative of calcium and how is this information translated into steering the tail? The authors describe a chemical differentiator model, in which calcium binds with differing strengths to proteins with opposing control of the tail. It’s all about chemistry!

Original Paper: Alavarez et al., 2012 J Cell Biol. http://jcb.rupress.org/content/196/5/653.full

Full Movie: http://jcb.rupress.org/content/196/5/653/suppl/DC1

☼ SPECIAL THANKS to Kevin Staff for making this animated Gif and for being the tail that wags my #ScienceSunday posts! Konstantin Makov is hereby challenged to come up with mood music for the sperm turns 😉

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25 Responses to A Sperms Tale: Calcium gets the Turn On! Wonder how a sperm finds the egg?

  1. Thank you for sharing this Rajini, its stuff(not necessarily sperm) like this that keeps me motivated to keep on truckin in Chem class.

  2. Rajini Rao says:

    I didn’t know you were taking Chemistry, William Tatum , that’s great 🙂

  3. I sat down and really thought about what I want to “do”, i want to work on brain machine interfaces and everything I have read as a lay person tells me that Chemistry is the way to go, its generally useful in a variety of different ways for solving the problems of interfacing with neurons. Biology is just applied Chemistry.

  4. Chad Haney says:

    William Tatum I feel sorry for you when you get to PChem class. :~)

  5. Rajini Rao says:

    I realize this post is dense and may be difficult to digest, so feel free to shoot me questions if I was unclear 🙂

  6. So when you say ” In other words, sperms respond to change, not absolute levels of signal.” are you saying that its more digital, like pressing a button, vs analogue turning a dial? If so, is there a “circuit” somewhere in the flagellum that is being completed by some concentration of Ca2+ ions or is just the presence of an ion sufficient to cause the tail to “wag” in one direction or another? And is this a “homing device” because the Egg is releasing Ca2+ ions? If so why is it doing that, what other reaction is going on that precipitates the Ca2+, or is it just a concentration gradient like with ADP to ATP?

  7. Rajini Rao says:

    Chad Haney , I hate to admit it, but I feel the same way 😉

  8. William Tatum biochemistry is the real deal.

  9. Rajini Rao says:

    William Tatum , the egg is not releasing Ca2+ ions, but a chemical attractant that is sensed by the sperm. Calcium comes into the sperm from the outside via open channels (because of a 10,000 fold gradient that is larger outside, tiny inside). The rapidity which which it enters is sensed by calcium binding proteins. Re. your digital vs. analog question, my guess is that at the molecular level, it is digital..like an on off switch. But averaged out over thousands of molecules, it looks like an analog signal. The binding of calcium influences the turning of the flagellum.

  10. Rajini Rao says:

    Prabat parmal , dF/dT is not digital, as you have observed. That is because it represents the thousands of calcium ions bound to the detector that is then fluorescing. I am referring to what the calcium does next. It binds to a biological detector, a protein, that then responds by changing its function. At the individual level, binding and functional changes (caused by change in the protein shape..known as conformational change) is termed “stochastic”. It is defined by a probability function and represents a digital signal.

  11. Rajini Rao is correct. Individual proteins will be either in the “on” conformation, or in the “off” conformation, depending on calcium binding, Once calcium ions reach certain threshold they can bind individual molecules of protein switching the protein from off to on. But there are no proteins partially on.

  12. Rajini Rao says:

    That’s a pretty cool concept, isn’t it Gustavo MacIntosh ? 🙂 Animations that show individual motors zooming along smoothly or enzyme molecules turning over reactions evenly are actually inaccurate. I was meaning to explain this to Gnotic Pasta , who asked me about those attractive cell animations by Drew Berry featured on TED. Drew Berry: Animations of unseeable biology

    On the one hand, I like them because it lets people glimpse into the inner working of a cell. On the other hand, I cringe a bit at the parts that are not accurate at a molecular level 🙂 Overall, they are pretty cool, though!

  13. I agree Rajini Rao, some animations are a good teaching tool, but it always depends on the level that you would like to teach. I find myself showing animations, but then “correcting” half of what is shown. In some cases it shouldn’t be so difficult to show a more correct representation, may be we should start asking for them.

  14. Robby Bowles says:

    I love how gifs works so well on this platform Rajini Rao, hope you don’t mind that I’m starting to play around with them some as well :).

  15. Rajini Rao says:

    Robby Bowles , gifs are better than videos for a couple of reasons. First, there is the instant draw of attention, whereas the video requires at least one click to get going 🙂 Also, if the video is on YouTube, then it’s an easy embed, but if you have to upload it then there is an appreciable delay in opening the image window, and loading it which could be really bad for people with slow connections. Most science videos are large, so the compromise is to link to the video but extract basic information into an animated gif. I will admit to no technical knowledge on making the gif myself 😉 I would love to see what you come up with!

  16. Norman M. says:

    Drilling down to the details, now the perfume industry is going to add Calcium Attractors with names such as Calexy. 🙂

  17. Rajini Rao “The binding of calcium influences the turning of the flagellum.” -Smells more Robotic than Life. 🙂

    So, females good controllers by inheritance. I truly bow down before the femininity.

  18. Tom Lee says:

    Rajini Rao Didn’t know the scope of your research also cover stuff like sperm chemistry. These are information that are so informative. Gifs and video are both good if the contents are explained better in the gifs, or video. Video has sound though, while gifs don’t.

  19. Neil Tsubota says:

    I thought it was “random” chance. Probability of occurence of “Heads/Tails” on a coin flip is 50/50. Probability of a BOY or GIRL is 50/50. We can not have any other outcome !

  20. Very informative ! thanks for sharing.

  21. Rajini Rao says:

    Sarabjit Kahai , wow, what a nice thing to say! Thank you so much.

  22. Rajini Rao says:

    Tom Lee , I work on calcium signaling in cells, not sperm. But the principles are the same. You raise a good point about lack of sound/music on a gif. So it is a trade off.

  23. Rahul Joshi says:

    Guess it’s time I buy that Calcium Sandoz bottle xD

  24. HeyHey… Hang on there I believe that the company has abandoned the prodo of that popular media long back on some grounds(i,ve4gotten why ) so as such u may haf2 look4another vendor or alternative…

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