A potential new contributor to obesity--faulty cilia--has been discovered by researchers at Johns Hopkins University, Baltimore, Md. Many a high school biology student has glanced into a microscope to see the planet's smallest animals--paramecium and the like--being propelled by the waving, hair-like projections known as cilia. Yet, cilia also are found in human cells, helping move fluid and mucous around in the brain, lungs, eyes, and kidneys, or sticking out from cells to act like antennae. Studying families with a relatively rare condition called Bardet-Biedl syndrome (BBS), characterized by obesity, learning disabilities, and eye and kidney problems, the researchers uncovered a new gene. Furthermore, the gene's protein, BBS8, is found only at the base of cilia.
Bardet-Biedl syndrome (pronounced BAR-day BEED-el) "is a relatively rare genetic disorder, but it has traits common to many people," declares Nicholas Katsanis, assistant professor in the McKusick-Nathans Institute of Genetic Medicine. "We don't know yet how the ciliary defect might lead to obesity or learning disabilities, but the finding provides a new avenue to studying these genetically murky traits. It is very difficult to translate genetic understanding into a cellular mechanism that explains what is seen in a disease."
Some aspects of BBS have been linked to ciliary defects in other conditions. Cilia are known to play key roles in mammalian development, creating what is known as left-right asymmetry so organs like the heart, lungs, and liver end up in the correct place. In people with BBS, sometimes left-right asymmetry is reversed. Also, malfunctioning cilia in the back of the eye can cause retinal dystrophy and eventual blindness, and ciliary difficulties in the kidney lead to structural complications in the organ.
Even though these primary characteristics of Bardet-Biedl have been tied to ciliary defects, the condition itself and its other traits-extra fingers and diabetes--never have been linked to cilia before. These syndrome characteristics may be caused by defects in the cellular mechanics, but the research finding opens a never-before-pursued channel to understanding these attributes in the general population.
Katsanis says the next step is to figure out exactly what is wrong with the cilia and how those defects affect different tissues. The answer could lie in ciliary movement or in their ability to sense cells' surroundings. "Cilia are very overlooked. The majority of cilia in human cells act as a sort of communication device, which isn't the typical picture of waving, mobile cilia. Cilia can act as cells' private satellite dish."
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