Notoriously camera-shy sperm caught spiraling in 3-D
Sure sperm swim. I’ve seen Look Who’s Talking and the Miracle of Life. Turns out that in real life, there’s actually a lot of spiraling.
Researchers developed a new lens-free, 3-dimensional imaging technique for the first large-scale, high-resolution recordings of human sperm in three dimensions. They revealed spiraling movements that had previously only been inferred from 2-dimensional data, Nature News reports.
“This is the first observation of something that was entirely hidden,” says study researcher Aydogan Ozcan at the University of California, Los Angeles. The recordings tracked over 1,500 cells over several hours… detailed observation that sperm have eluded in the past.
Their heads are just 3–4 micrometres long and can only be seen under high magnification, but the cells zoom around at up to 100 micrometres per second, ducking in and out of focus or darting out of range in an instant.
High-powered microscopes can show detailed cellular structures, but the field of view is too small to follow the paths of swiftly moving microorganisms, ScienceNOW explains. So the team sidestepped that obstacle by getting rid of the lens.
- The team watched the sperm with a tiny sperm-sized, light-sensing chip placed underneath the translucent sample.
- A red LED shines down on the sperm, forming a hazy shadow on the chip that follows the head of each cell as it moves horizontally.
- A second, blue LED illuminates the sperm from a different angle, casting shadows that change with each sperm head’s vertical position.
- Imaging cells en masse at about 90 frames per second allowed the researchers to characterize sperm movement more precisely than ever before.
More than 90% of the sperm moved along slightly curved paths, wiggling their heads slightly from side to side. Another 4–5% traveled in near-perfect spirals, following a corkscrew path.
Watch a delightful video of the helical swimmers here, and below.
The method can be used to study sperm under a wide range of physiological conditions, including the pH and fluid conditions encountered en route to an egg. The imaging could lead to cheaper and more portable ways for fertility researchers to look at sperm movement, replacing costly computer systems that analyze microscope images. The technique could also be used to study bacteria and other swimming microorganisms.
The study was published in Proceedings of the National Academy of Sciences yesterday.
Image: Ozcan Research Group at UCLA