Earlier, I explained how we can reasonably look at cilia from a teleological perspective. I later provided a clue to support my hypothesis. The hypothesis even made my oh so prestigious top 10 list for 2010!
So now consider the fact that while scientists have long considered the primary cilia to be some functionless vestige, it turns out they function as sophisticated communication devices because of intraflagellar transport:
Nearly all mammalian cells have what’s called a primary cilium — a single, stump-like rod projecting from the smooth contours of the cell’s outer membrane. Unlike its more flamboyant cousins, the motile cilia, which beat industriously in packs to clear our airways of mucous or to shuttle a fertilized egg to the uterus, the primary cilium just … sits there.
Like a bump on a log.
In fact, it looks so useless that, until recently, many scientists considered it to be just a leftover artifact of eons of evolution.
Recently, however, research has shown that defects in the development or function of primary cilia are associated with many human disorders, including polycystic kidney disease, skeletal malformations, neural tube defects as well as obesity. Clearly there’s more here than meets the eye. Scientists have since decided that the primary cilium works as a kind of antenna to help the cell respond to outside chemical signals and mechanical forces.
Now researchers at the Stanford University School of Medicine have pinpointed the molecular cause of a rare genetic disease in humans called Bardet-Biedl syndrome, or BBS. People with the disorder suffer from obesity, retinal degeneration, kidney cysts and polydactyly (having extra fingers or toes). And, as you might guess, it all hinges on the primary cilium. Specifically, the researchers have discovered that genetic mutations associated with the disease affect a protein complex that ferries receptors and other proteins from the cell’s membrane to the surface of the primary cilium.
“This provides a very logical explanation for the wide variety of symptoms seen in patients with Bardet-Biedl syndrome,” said Maxence Nachury, PhD, assistant professor of molecular and cellular physiology. “The primary cilium used to be thought of as just the appendix of the cell. Now we’re finding that it’s actually the communication hub where many signaling pathways take place.”