Based on limited published evidence, CSTPP1 is a regulator of the tubulin polyglutamylase complex (TPGC) that controls cytoskeletal organization, nuclear shape, and cilium disassembly by balancing microtubule and actin assembly 1. CSTPP1 regulates TPGC assembly and stability, modulating microtubule polyglutamylation to antagonize MAP4 binding 1. The protein localizes to centriolar satellites and functions in microtubule cytoskeleton organization through protein-macromolecule adaptor activity. Recent evidence suggests CSTPP1 expression is elevated in high-motility human sperm and may serve as a fertility biomarker 2.