Testis-predominant gene Mfap3l is dispensable for spermatogenesis under physiological conditions

The microfibril-associated protein (MFAP) family members play critical roles in extracellular matrix (ECM) assembly and tissue homeostasis maintenance. Among them, MFAP3L (microfibril-associated protein 3-like), a paralog of MFAP3, is predominantly expressed in testicular tissue. Conventional hypotheses propose that it may participate in spermatogenesis by regulating ECM remodeling; however, direct functional evidence and mechanistic insights remain limited. To test this hypothesis, we generated a systemic Mfap3l knockout mouse model using the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) technology to investigate its role in spermatogenesis. Unexpectedly, although Mfap3l is predominantly expressed in testis, Mfap3l ^-/- male mice exhibited normal fertility, with no significant defects observed during spermatogenesis. These results indicate that Mfap3l is dispensable for spermatogenesis and the maintenance of male fertility under physiological conditions. Furthermore, the findings also revealed no effective compensatory upregulation of other MFAP family members in the testes following Mfap3l knockout. This study challenges the conventional assumption that "genes predominantly expressed in the testes necessarily play a central role in reproductive regulation," providing an informative negative example for research on reproductive gene function and emphasizing the necessity of direct functional validation through gene knockout.