Non-motile Cilia

Non-motile cilia are also known as primary cilia. Primary cilia are extremely vital throughout development, performing critical functions in embryonic morphogenesis and organogenesis. Genetic mutations encoding cilia proteins cause a group of inherited developmental illnesses known as “ciliopathies.” The present state of knowledge on the role of these intriguing organelles in a variety of signalling pathways is summarised in this article. 

Primary cilia are microtubules that appear as solitary appendages on the apical cell surface and do not have a centre couple of microtubules (for example in a kidney tube). Ciliary proteins are made in the cell and must then be delivered to the axoneme’s tip. Anything about the function and structure of motile & primary cilia is still unclear, but we anticipate that greater investigation into these vital cellular components will eventually lead to better approaches to treat and assist people’s lives are disrupted by malfunctioning cilia.

Non-motile Cell 

Non-motile primary cilia can be found on virtually every type of cell in mammals, with blood cells being the notable exception. In comparison to cells containing motile cilia, most cells only have one, except olfactory sensory neurons, which have roughly 10 cilia each and include odorant receptors. Primary cilia are specialised cilia present in a variety of cells, including photoreceptors in the retina. 

For the next century, it was mostly ignored, and it was assumed to be a rudimentary organ system with no considerable effect. Its physiological role in chemosensation, cell signalling, and cellular growth control was recently revealed, highlighting its importance in cell function. The discovery of its role in a wide range of illnesses known as ciliopathies, which are caused by cilia dysgenesis or failure, including polycystic kidney disease, heart abnormalities, mitral valve collapse, and retinal deterioration, has highlighted its importance in social biology. 

The Aurora-A kinase is required for the disassembly of cilia. Primary cilia are viewed as “sensory cellular antennas that coordinate various cellular signalling pathways, sometimes connecting the signals to ciliary motion or alternative to cellular differentiation,” according to current scientific understanding.”The cilium is made up of subdomains and is surrounded by a cell membrane that is continuous with the cell’s plasma membrane. 

The basal body, from which the cilium emerges, is found within a membrane’s engulfment known as the ciliary pocket in many cilia. Distal appendages connect the cilium membrane to the microtubules of the basal body (transition fibres). At the distal appendages, vesicles transport chemicals to the cilia dock. A transition zone forms distant to the transition fibres, regulating molecule entry and exit to or from the cilia. Hedgehog signalling is one example of cilia signalling that occurs through ligand binding. G protein-coupled receptors, such as the nucleoside receptor 3 in neural cells, are another type of signalling.

Cilium: Structure

• Microtubules wrapped in a cell membrane make up a cilium. 

• The protein tubulin is used to make microtubules, which are hollow cylindrical rods. Each cilium has nine bundles of microtubules that create a ring around the outside and two microtubules in the centre. 

• This structure is called an axoneme, as well as the arrangement is called ‘9+2,’ which is common in motile cilia. 

• Cross-linking proteins hold the microtubules together. 

• Motor proteins named dynein are found between both the 9 outer pairs. 

• Cilia are indeed very small structures with a diameter of about 0.25 m and a length of up to 20 m. 

• They can be detected in vast quantities on the surface of the cell when they are present. The cilia beat back and forth like oars to create movement.

Role

Cilia are involved in movement and perform a crucial role. This can include the cell’s movement as well as the movement of other liquids and objects passing the cell. 

• Cilia are important in the formation of the entire organism in some species known as ciliates. 

• Cilia, for example, cover the top of the single-celled protist Paramecium and are important for both mobility and eating. 

• Cilia not only cover the surface of the organism but also border an oral groove, which allows food to enter the organism’s “mouth.” 

• By assisting in the movement of fluids over the cell, they can aid in the removal of pollutants from organs or tissue. 

• Cilia line the inside of the nasal passages and the trachea.

Conclusion

Ever since the 1960s, the presence of solitary, non-motile “primary” cilia on epithelial cells’ surfaces has been widely documented. For decades, however, these organelles were thought to be vestigial, with really no function after losing their motility. The essential significance of non-motile cilia in signalling pathways was not appreciated until 2003 when it was discovered that proteins essential for transportation all along primary cilium are required for hedgehog signalling in mice. After a little over a decade, it’s obvious that the primary cilium is involved in the overwhelming bulk of vertebrate signalling pathways. As a result, the primary cilium is now referred to as “the cell’s antenna.”