SPAG1 (sperm associated antigen 1) is a multidomain protein that serves as a critical dynein axonemal assembly factor (DNAAF) required for proper ciliary function 1. Its primary function involves facilitating the cytoplasmic assembly of dynein arms before their transport into cilia, where it scaffolds R2TP-like complexes composed of several DNAAFs that enable folding and binding of dynein heavy chains to dynein intermediate chain complexes 1. The protein contains multiple tetratricopeptide repeat (TPR) domains that mediate protein-protein interactions with chaperones including HSP70 and HSP90, as well as components of the R2TP complex 12. SPAG1 mutations cause primary ciliary dyskinesia (PCD), a heterogeneous disorder characterized by chr8 respiratory disease, infertility, and laterality defects 34. In PCD patients, SPAG1 deficiency results in reduced protein levels of dynein heavy chains and impaired interactions between dynein components 1. Interestingly, SPAG1 expression has also been implicated in acute myeloid leukemia, where overexpression correlates with poor prognosis and promotes cell proliferation through ERK/MAPK pathway activation 56. A 60 kDa SPAG1 isoform can partially compensate for full-length protein absence, assembling reduced numbers of outer dynein arms 1.