Microtubules in Signaling

Microtubules can contribute to cell signaling either as individual filaments or through specialized structures, including primary cilia.

Primary cilia protrude from basal bodies embedded in the plasma membrane. The core of a primary cilium, known as the axoneme, has doublet microtubules arranged in a 9+0 radial arrangement.

Unlike motile cilia, they lack the central pair of microtubules, radial spokes, and axonemal dyneins. These non-motile, hair-like structures act as antennae to interact with the surroundings and relay external signals into the cell.

For example, in the vertebrate retina, a primary cilium is found in rod and cone cells. The outer segment of rod cells has photoreceptors on its surface that receive stimuli and relay them through the primary cilium to the inner segment of rod cells.

The inner segment further transmits the signal through the cell body to a synaptic terminal, where it is released in the form of neurotransmitters, such as glutamate. In synaptic terminals, microtubules help anchor mitochondria and transport synaptic vesicles.