Reduced Sperm Counts in Mice with Dmd Exon 51 Frameshift Mutations

Background/Objectives: Duchenne muscular dystrophy (DMD) is caused by frameshift mutations in the DMD gene encoding dystrophin. Beyond skeletal muscle, dystrophin's full and shortened isoforms are expressed in non-muscle tissues, including the male reproductive system, where it is reported to engage in spermatogenesis, sperm motility and overall fertility in patients and mouse models. We have previously generated two genetically modified mouse strains carrying insertions (insT or insG) in exon 51 of the Dmd gene to model DMD. Here, we characterize male fertility and related reproductive phenotypes in both strains. Methods: Fertility was assessed by mating, recording copulatory plugs, litter production and pregnancy rates over an extended breeding period. Sperm concentration and motility were quantified in vas deferens samples. Testicular dystrophin expression was evaluated by qPCR and immunofluorescence. Germ cell populations were examined by flow cytometry of testicular cell suspension; H&E histology with morphometry of tubular and peritubular compartments was carried out, along with immunofluorescence for cytoskeletal markers (dystrophin, actin, vimentin). Results: Both strains retained immunoreactivity for an N-terminal/rod-domain dystrophin epitope in testes, with modest nonsense-mediated decay of Dp427m transcripts and unaltered Dp71 levels. In a small breeding trial, mutant males, especially insG, produced fewer offspring despite comparable litter sizes, with fewer pregnancies after a copulatory plug. Sperm concentration in the vas deferens was approximately halved in both strains, with occasional azoospermia. Flow cytometry showed a selective decrease in the mature haploid (elongating) population in insG animals. Conclusions: In exon-51 frameshift models, the phenotype is lower sperm concentration in the vas deferens, to roughly half of control levels, with occasional azoospermia. InsG also fails to maintain a normal elongating-to-round spermatid ratio. Whether this fully accounts for the poorer breeding performance in the cohorts studied remains open. Overall, these findings underscore the functional role of dystrophin in spermatogenesis.