Intraflagellar

Intraflagellar refers to processes that occur within the flagellum or cilium, particularly those related to intraflagellar transport (IFT). IFT is the bidirectional movement of multiprotein complexes along the axoneme of cilia and flagella, essential for their assembly, maintenance, and signaling capabilities. The phenomenon has been studied in diverse eukaryotes, from the green algae Chlamydomonas reinhardtii to mammalian cells.

The transport system is organized into two main protein complexes, IFT-A and IFT-B, which form trains that travel along the microtubule-based axoneme. Anterograde transport, moving toward the distal tip, is driven by kinesin-2 motors and delivers building blocks and signaling components required for ciliogenesis and function. Retrograde transport, moving toward the base, is driven by dynein-2 and recycles deteriorated material and signaling receptors back to the cell body. The coordinated activity of IFT trains is necessary for proper ciliary length, composition, and responsiveness to environmental cues.

Disruptions to intraflagellar transport can impair ciliogenesis and ciliary function, contributing to a class of disorders known as ciliopathies. These conditions include polycystic kidney disease, Bardet-Biedl syndrome, Joubert syndrome, and other developmental anomalies, reflecting the central role of IFT in sensory perception and developmental signaling pathways such as Hedgehog signaling in vertebrates.

In literature, intraflagellar is used as an adjectival term describing processes inside cilia and flagella, with intraflagellar transport being the principal intraflagellar process described.