Cilia
Why should I be interested in Cilia?
Cilia are structures found on almost every cell in our bodies. Scientists currently think that the symptoms in LMBBS patients are caused by cilia not working properly.
What are Cilia?
Cilia (singular – cilium) are thin, tail-like projections extending approximately 0.1 mm outwards from the cells. There are two types of cilia, motile cilia (moving cilia) and non-motile cilia. Motile cilia constantly beat in a single direction, whilst non-motile cilia typically sense the cells’ environment. Non-motile cilia are often referred to as ‘primary’ cilia.
What do they do:
As the name suggests, motile cilia are involved in movement. As they constantly beat in a single direction, they can help a cell move around. They also do the job of moving other ‘things’ (fluid) along. As these types of cilia are usually present on a cell’s surface in large numbers, they beat in coordinated waves. An example of motile cilia can be found in humans in the lining of the windpipe, where they sweep mucus and dirt out of the lungs.
Normally a cell only has one non-motile cilium. There are some cells in the body that have a specialized primary cilium which have a very important job to do.
For example in the human eye, there is a primary cilium that connects the outer segment of the rod photoreceptor cell to its cell body. When you get problems with these cilia that you can get retinitis pigmentosa (RP).
Though the primary cilium has historically been ignored by scientists, research has now shown that this structure is involved in many important cell processes such as sensing its environment, cell growth and also cell development. These recent findings have led scientists to re-evaluate the importance of this structure. This is what has made LMBBS a well known cilia disease.
What are cilia of and how do they work?
A cilium is put together from smaller building blocks. The main component of these building blocks is a protein called “tubulin”, however other proteins are also involved. Cells need to maintain their cilia and supply them with materials. Proteins and other cargo are moved up and down the cilium by “molecular motors”. This process is called intraflagellar transport and it is vital for the maintenance and function of the cilium.
This is a picture of a cilium showing where the BBS proteins are. Most of them sit at the bottom of the cilia, at a place called the basal body. The basal body is like the anchor of the cilium, joining it to the cell. Many of the BBS proteins are involved in intraflagellar transport and so can be found along the cilium as well.
What happens when things go wrong?
Cilium-related diseases
Sometimes cilia don’t function properly. This is usually because of a problem with the intraflagellar transport. This causes problems in cells, especially the ones that rely heavily on specialized cilia, such as the photoreceptor in the eye and particular cells in the kidney.
Diseases where there are problems with cilia are called ciliopathies. LMBBS has been classified as one such ciliopathy, others include Alström syndrome, Meckel-Gruber syndrome and nephronophthisis. Scientists are still trying to find out exactly how the problems at the cilia lead to the symptoms of the disease.
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