Cilia - the prodigal organelle
Cilia are the oldest known cellular organelle, firstdescribed in 1675 by Anthony van Leeuwenhoek in protozoa. He described them as 'incredibly thin feet, or little legs, which were moved very nimbly'.
The term 'cilium'(Latin for eyelash) was probably first coined by Otto Muller in 1786 . Structurally and functionally similar to eukaryotic flagella, cilia were originally defined by their motility and for many decades this was their only ascribed purpose.
During the latter half of the 19th century came the observation of another class of solitary cilium, which for the most-part was non-motile [3-5]. Zimmerman, who first described 'centralgeissel'(central flagella) in mammalian cells also proposed a sensory role for them, but they received little attention thereafter .
The organelle was renamed 'primary cilia'in 1968  because the primary cilium was noted to appear first before multiciliated cellsappear in the central nervous system. But their function remained elusive until this past decade.
In fact, the revelationthat primary cilia have a sensory role, signalling to the cell interior external cues which underlie many human diseases, has somewhat eclipsed research into motile cilia. This split with two cilia categories is however, short lived as more recent evidence indicates that, as long suspected, motile cilia/flagella also have sensory potential (see  for a review).
Published on: 2012-04-25