TEKT4 (tektin 4) is a microtubule inner protein that plays essential roles in sperm motility and flagellar function. The protein forms filamentous polymers within the walls of ciliary and flagellar microtubules, contributing to the structural integrity of the axoneme 1. TEKT4 is predominantly expressed in male germ cells, particularly in haploid round spermatids, and localizes to sperm flagella 1. Loss of TEKT4 function severely impairs sperm motility, causing reduced forward progressive velocity, uncoordinated waveform propagation, and approximately 10-fold higher ATP consumption compared to wild-type sperm 1. While flagellar ultrastructure remains grossly normal in TEKT4-deficient sperm, the coordinated beating mechanism is disrupted, leading to subfertility in male mice 1. In humans, decreased TEKT4 expression has been associated with idiopathic asthenozoospermia, suggesting its clinical relevance in male infertility 2. Beyond reproductive biology, TEKT4 has emerged as a potential biomarker in cancer research, with variants associated with paclitaxel resistance in breast cancer through effects on microtubule stability 3, and mutations identified in various cancer types including non-small cell lung cancer and papillary thyroid cancer 45.