Meiosis-arrest female 1 (MARF1) is a recently identified key oogenic regulator essential for the maintenance of female fertility and genome integrity in mice.However,the detailed functions and the underlying mechanisms of MARF 1 remain elusive.Here,in an attempt to create a mouse model expressing fluorescent protein-tagged MARF 1 to facilitate further exploration of the roles of MARF 1 in oocytes,we produced a Marf1-eGFP knockin (KI) mouse line in which the C-terminal structure and function of MARF1 were interfered by its fusing eGFP peptide.Using these Marf1-eGFP-KI mice,we revealed,unexpectedly,the functions of MARF1 in the control ofoocyte meiotic division.We found that the Marf1-eGFP-KI females ovulated mature oocytes with severe meiotic and developmental defects,and thus were infertile.Moreover,meiotic reinitiation was delayed while meiotic completion was accelerated in the KI-oocytes,which was coincident with the increased incidence of oocyte aneuploidy.Therefore,MARF1 is indispensable for maintaining the fidelity of homolog segregation during oocyte maturation,and this function relies on its C-terminal domains.