Question: Are primary cilia like membrane receptors and if so what role do they play in cell-to-cell communication?

Laura Devlin answered on 1 May 2020: last edited 1 May 2020 10:15 am

Hi,
Thank you for your question about the primary cilium! The primary cilium sticks out of the cell, like an antenna, and it extends from the normal plasma membrane of the cell, into its own specialised membrane. You are correct, it does act a bit like a receptor but, it is more like one big signalling hub, because on its membrane it can have lots of different receptors and ion channels. There is also only one primary cilium on a cell.

What is cool is that the primary cilia itself is like it’s own very special compartment, where entry of receptors, channels, and other signalling proteins are very tightly controlled, as well as what can leave the primary cilium. This makes it a well designed structure for controlling cell signalling, as a lot of the receptors are concentrated to this site.

We are still trying to understand all of the communication roles that utilise the primary cilium, but one more established signalling pathway is called Hedgehog Signalling, where the ligand ‘sonic hedgehog’, binds to it’s receptor on the primary cilium, which sets off a signalling pathway to the nucleus of the cell, which effects expression of other genes. Hedgehog signalling is very important in development; the development of the vertebrae limb requires hedgehog signalling. Hedgehog signalling also has roles in adult stem cells. There are other chemical signalling pathways that use the primary cilium for cell-to-cell communication, such as Wnt, which can effect cell polarity (direction) and divisions, and Notch which important in lots of cell differentiation processes amongst other processes. Let me know if you would like to know more.