TEKTIP1 is a microtubule inner protein (MIP) localized at the center of the tektin bundle within dynein-decorated doublet microtubules of cilia and flagella axonemes. Based on limited published evidence, TEKTIP1 functions to stabilize the tektin bundle and is required for normal sperm flagellar motility 1. Loss of TEKTIP1 results in male subfertility through reduced sperm motility and disorganized axonemal structures, primarily by affecting TEKT3 organization and tektin interactions 1. TEKTIP1 deficiency may be relevant to human asthenospermia.