Mouse Genome Engineering Uncovers 18 Genes Dispensable for Male Reproduction
18 testis-enriched genes knocked out one by one in mice — none of them mattered for fertility
Journal: Andrology | Published: 2025-06-26 | Type: Animal knockout study | PMID:40572022Authors: Chang Hsin-Yi, Lu Yonggang, Yamamoto Kaito, et al. (University of Osaka, Research Institute for Microbial Diseases)
Funding/COI: NICHD/NIH, Japan Society for the Promotion of Science, Asahi Glass Foundation, Takeda Science Foundation. No conflicts of interest declared.
Summary
Researchers at Osaka used CRISPR/Cas9 and classical gene replacement to knock out 18 genes that are highly expressed in mouse testis and epididymis. Every single knockout male was fertile, with normal sperm morphology, motility, and testis histology. The paper is a negative result — deliberately so — arguing that publishing "dispensable" gene lists is as useful to the field as publishing essential ones.
Claims
All 18 knockout male mice displayed normal fecundity, litter sizes comparable to wild-type controls, and no abnormalities in testis weight or histology
Sperm motility and morphology were unaffected in all 18 lines
Glipr1l1 knockout alone impairs the acrosome reaction in vitro, but a triple knockout of all three GLIPR1-like proteins (Glipr1l1-3) still produced fertile males — the family appears collectively non-essential
Triml1 and Triml2 were knocked out together given their sequence homology; the double knockout was also fertile
Several candidate genes, including Glipr1l3 and Pin1rt1, exist only in mice and have no human orthologs
Efcab15 is a protein-coding gene in mice but annotated as a pseudogene in humans (EFCAB15P)
Fam24b is testis-specific in mice but ubiquitously expressed across human tissues
Study Quality
This is a methodologically competent mouse mutagenesis paper. CRISPR/Cas9 (and one conventional gene replacement) are established tools; the genotyping and phenotyping pipeline — fertility assays, testis histology, sperm morphometry, motility analysis — covers the standard bases. Depositing frozen sperm lines in public repositories (RIKEN BRC, Kumamoto CARD) earns credit: other labs can use these knockouts without rebuilding them.
The study design is inherently limited in one direction: it tells you these 18 genes are individually non-essential in a laboratory mouse under standard conditions. It says nothing about combined effects beyond the Glipr1l1-3 triple and Triml1/2 double knockouts, and it cannot account for evolutionary pressures (sperm competition, heteromorphism) that may have maintained these genes despite their apparent redundancy in the lab. The authors acknowledge this explicitly, which is the right call.
Red Flags
Mouse-to-human translation is uncertain throughout. Some genes tested are mouse-specific; others have divergent expression patterns in humans. The authors' extrapolation that "mutations in these genes may not impair fertility in men" is speculative and unsupported by human genetic data
Transcriptional compensation is unaddressed experimentally. The authors cite it as a known caveat but do not measure compensatory upregulation in any of the 18 knockouts — so null phenotypes may reflect redundancy rather than true dispensability
No stress testing. Laboratory fertility assays under ideal conditions may not catch subtle defects. Competitive fertilization assays or sub-optimal mating scenarios were not reported
Single-locus knockouts dominate. Only two multi-gene knockouts were tested; the remaining 16 genes were each disrupted individually, leaving combinatorial effects unexamined
Sample sizes per line are not specified in the abstract or extracted sections — critical for interpreting the confidence in "normal" phenotypes
Strengths
Negative result papers are systematically undervalued and underproduced; this one accelerates the field by ruling out 18 candidates
CRISPR/Cas9 delivery via zygote electroporation is current best practice for mouse knockout generation
Multi-metric phenotyping (fertility, histology, sperm parameters) rather than relying on a single readout
All mouse lines deposited in accessible public biobanks for community reuse
No industry funding; no conflicts of interest
Honest about the mouse-specific gene problem and the speculative nature of human predictions
Verdict
This is useful, unglamorous science. The finding that 18 testis-enriched genes are individually dispensable in mice is not exciting, but it trims the candidate list for anyone investigating genetic causes of male infertility — which affects roughly 7% of men and remains genetically unexplained in the majority of cases. The extrapolation to human fertility is the paper's weakest point: several genes tested either don't exist in humans or behave differently, and the authors lean harder on those translational implications than the data support. Read it as a mouse genetics paper, and it delivers what it promises.