RIBC2 (RIB43A domain with coiled-coils 2) is a microtubule inner protein (MIP) localized to the inner lumen of dynein-decorated doublet microtubules (DMTs) in cilia and sperm flagella 1. The protein is part of the axonemal structure required for motile cilia beating and sperm flagellum function 1. RIBC2 expression is regulated by a common functional variant rs2272804 in its 5'UTR that creates an upstream open reading frame, reducing translational efficiency by 85% 2. In vivo studies demonstrate that RIBC1 and RIBC2 function cooperatively to regulate sperm motility; double-knockout mice show significantly reduced sperm velocity and decreased litter size, though axonemal structure remains intact 3. Beyond its ciliary role, RIBC2 is aberrantly regulated in multiple cancers and disease states. Hypomethylation of RIBC2 CpG sites associates with Vogt-Koyanagi-Harada disease pathogenesis 4. RIBC2 is upregulated in esophageal cancer and serves as a diagnostic/prognostic biomarker linked to unfavorable clinicopathological features and immune-excluded tumor microenvironments 5. Additionally, RIBC2 is identified as a prognostic hub gene in cervical cancer and hepatocellular carcinoma signatures 6, 7, 8. These findings reveal RIBC2's dual role in ciliary function and cancer-associated pathways.