Hydin KO causes hydrocephalus and lethality before sexual maturation, which hampers the analysis of the mature spermatozoa.28 Recently, we knocked out Hydin in fluorescently tagged ES cells using the CRISPR/Cas9 system.26 By making chimeric mice with these ES cells, we were able to analyze spermatozoa derived from Hydin KO ES cells and we found that HYDIN is essential for flagellum formation.26 To analyze if KIF9 is associated with HYDIN in mice, we analyzed KIF9 localization using these chimeric mice. Here, HYDIN is linked to Hydrocephalus.