The Delicate Balance of Ear Crystals


UCLA researchers have discovered that tiny crystals called otoliths—necessary parts of a properly functioning inner ear—form not as the direct result of a gene product, but rather as the result of the physical, swaying motion of hair-like cilia during development.

As adult vertebrate bodies move about, otoliths are pulled by gravity and enable the detection of movement, which is vital for maintaining balance. The researchers studied these crystals in fish embryos, where they accumulate as gelatinous proteins mixed with calcium carbonate. When fully and properly formed, the crystals lie atop sensitive beds of cilia, which are fine, hair-like cellular extensions that are responsible for translating roll, pitch, and yaw information from the semicircular canals of vertebrates’ ears.

In their study published in Nature, the scientists discovered that otolith formation required more than just genes—in this case, properly functioning cilia.1 This represents another example of an “epigenetic” factor influencing development, whereas a few short years ago scientists thought that purely genetic causes were responsible for the formation of biological structures.

But there is additional significance to this research. The researchers disabled the gene for the protein dynein, the molecular motor responsible for ciliary motion. The result was that the otoliths “did not assemble in the correct site. So not only did ear crystals form in the wrong place, but they were misshapen and abnormally sized,” according to co-author Kent Hill.2 So the crystals, rows of cilia, sensory cells, skull cavities, inner ear membranes, neuron connections, and many other parts must each be correctly formed for vertebrates to detect motion.

Not only are otoliths complex (being a crystalline arrangement of matter), but their timed and directed formation must result in the correct placement, shape, number, and size for balance detection to work at all. The same Creator who “curiously wrought” us in our mothers’ wombs,3 has similarly set up ciliary swaying as the means to build vertebrate ear otoliths. These crystals’ role in maintaining balance, as well as the precise requirements of their construction, shows clear indications of the Creator’s hand.

References

  1. Colantonio, J. R. et al. The dynein regulatory complex is required for ciliary motility and otolith biogenesis in the inner ear. Nature. Published online prior to print November 30, 2008, 8.
  2. Schmidt, E. Can you hear me now? How the inner ear's sensors are made. UCLA press release, November 30, 2008.
  3. Psalm 139:15.

* Mr. Thomas is Science Writer.

Article posted on December 9, 2008.