Flagella and cillia are both membrane-bound projections from the cell surface that beat in distinctive patterns. Cilia are shorter and usually more profuse than flagella and contain a microtubule cytoskeleton, the ciliary axoneme, surrounded by a ciliary membrane. The ciliary membranes of all cilia hold specific receptors and ion channel proteins that initiate signaling pathways that regulate motility and/or link mechanical or chemical stimuli to intracellular transduction cascades regulating differentiation, migration and cell growth during development and in adulthood. KPL2, also known as SPEF2 (sperm flagellar 2), is a 1,822 amino acid protein that contains a calponin homology domain, three nuclear localization signals, a consensus P-loop and a proline-rich region. Required for correct axoneme develoment, KPL2 is predominantly expressed in cells with cilia or flagella. Four isoforms of KPL2 exists as a result of alternative splicing events.