Fasciclin

Fasciclin refers to a family of cell adhesion proteins named for their role in mediating fasciculation, the bundling of nerve fibers during development. The most studied members are Fasciclin I (Fas1) and Fasciclin II (Fas2) in insects, where they were first described in Drosophila melanogaster. These proteins contribute to the proper organization of neural circuits by promoting interactions between growing axons and guiding their pathfinding.

A defining feature of fasciclins is the presence of a conserved extracellular fasciclin domain (often referred to as the Fas1 domain) that mediates adhesive interactions. The overall domain architecture can vary among family members: some are membrane-anchored proteins, others are secreted, and some contain additional adhesive or signaling modules. The fasciclin domain has been identified across diverse taxa, including in plants where fasciclin-like proteins participate in cell adhesion processes within tissues.

In insects, Fas1 and Fas2 influence axon fasciculation and the targeting of synaptic partners, contributing to the precise wiring of the nervous system. Disruptions in fasciclin function can lead to aberrant neurite bundling and connectivity defects, illustrating their role in neural development. In plants, fasciclin-like arabinogalactan proteins (FLAs) bearing the fasciclin domain are implicated in cell–cell adhesion, cell wall interactions, and various aspects of organ development, such as roots and flowers, underscoring a broader role for fasciclins beyond the nervous system.

Overall, fasciclins represent a conserved family of adhesion-related proteins with important functions in tissue organization and development across multiple lineages, and they continue to be explored to understand adhesive mechanisms in biology.