The DNA mismatch repair protein Msh4 is essential for meiosis of male but not for female in zebrafish.

Meiotic recombination plays a crucial role in the correct separation of homologous chromosomes. The DNA mismatch repair protein Msh4 is a meiosis specific protein and msh4 defects were reported to associate with azoospermia and ovarian dysfunction in mammal. However, its role has not been elucidated in an important model animal, zebrafish. Here, we examined the role of Msh4 in meiosis and gametogenesis by knocking out msh4 using CRISPR/Cas9 technology. The resultant msh4-/- mutants showed male predominance (98.5%) and brought asynaptic meiosis to form unpaired univalents evidenced by the immunofluorescence detection of the synaptonemal complex protein Sycp3 and Sycp1, and the recombination protein Rad51. Such unusual meiotic configurations led to meiotic arrest and subsequent abortive spermatogenesis. In contrast, msh4 deficiency induced infrequent msh4-/- female (1.5%) that laid eggs which developed to normal (40-80%) or abnormal (20-60%) progeny by fertilizing with sperm of wild type. Thus, Msh4 is essential for the meiosis in males, but is not strictly required in females.