Filippi syndrome-associated CKAP2L modulates microtubule dynamics essential for mitosis and ciliary length regulation.

Mutations in the gene encoding cytoskeleton-associated protein 2-like (CKAP2L) have been identified as a causative factor for Filippi syndrome, a rare developmental disorder characterized by facial dysmorphism, syndactyly, and microcephaly. However, the cellular and molecular mechanisms by which CKAP2L contributes to the pathogenesis of this syndrome remain largely unknown. Here, we generated a Ckap2l knockout mouse model to investigate the in vivo and cellular roles of CKAP2L. Interestingly, Ckap2l knockout mice show no overt developmental abnormalities, with the exception of reduced male fertility, evidenced by decreased sperm count, impaired motility, and abnormally elongated flagella. At the cellular level, CKAP2L is a bona fide microtubule-associated protein that localizes to microtubule-based organelles, including the centrosome, mitotic spindle, and ciliary basal body. Depletion of CKAP2L leads to shortened mitotic spindles and cytokinesis failure, resulting in multinucleation. Furthermore, we uncover a conserved function for CKAP2L as a negative regulator of primary cilium length; its loss markedly increases ciliary length in both human and mouse cells. Collectively, these findings position CKAP2L as a multifunctional regulator of microtubule-based organelles and suggest that Filippi syndrome can be classified as a 'centrosomopathy' arising from concurrent defects in cell proliferation and ciliary function.