Mice engineered to lack a sperm tail protein called CFAP77 had sluggish sperm and fewer pups, but weren't infertile
Journal: Andrology | Published: 2025-11-29 | Type: Journal Article, Research Support, Non-U.S. Gov't | PMID: 41316927 Authors: Wang Haoting, Pham Anh Hoang, Luo Mengjiao, Ikawa Masahito, Miyata Haruhiko (Research Institute for Microbial Diseases, The University of Osaka, Japan) Funding/COI: Funded by NICHD/NIH, Japan AMED, JSPS KAKENHI, MEXT, and JST. COI not listed in the record.
Wang et al., 2025 knocked out the gene for CFAP77, a structural protein inside the sperm tail's microtubule scaffold, in mice. The knockout males made structurally normal sperm that swam poorly and produced significantly fewer pups per mating than wild-type males, though they weren't completely sterile. The mechanism traced back to a second protein, TEKTL1, which depends on CFAP77 to stay put in the sperm tail.
This is a knockout mouse study, the standard causal-inference tool for assigning gene function, and the group used CRISPR-Cas9 with confirmed deletion by PCR/Sanger sequencing plus immunoblot confirmation of protein loss. Motility was quantified with computer-assisted sperm analysis rather than eyeballing, and the interactome was mapped with mass spectrometry rather than assumed. The follow-up Tektl1 knockout experiment is a reasonable attempt to dissect whether the motility defect runs entirely through TEKTL1 loss or has an independent component.
The fertility cohort is small: five knockout males tested individually against females, and the founder line itself derived from a single mutant pup out of seven born from 90 electroporated zygotes. Small founder pools raise the usual concerns about off-target effects and genetic drift in a knockout line, though the phenotype (motility defect, protein-level confirmation) is internally consistent enough to make a technical artifact unlikely. As with any mouse model, the jump to human male infertility is not established here; the paper only confirms CFAP77 is present in human sperm by immunoblot, nothing more.
A solid, appropriately-scoped mouse knockout study that does what it sets out to do: establish CFAP77 as necessary for normal sperm motility and identify a plausible mechanism (destabilization of TEKTL1) rather than overclaim a fertility "cure" or "cause." The small animal numbers and mouse-only scope mean this is basic mechanistic biology, not a finding with immediate clinical relevance, but the methodology is careful and the conclusions are appropriately hedged to match the data.