The Association Between Missense Mutation Of Meiob And Human Azoospermia

Meiosis is a unique,specialized cellular division process to produces haploid gametes from a diploid parental cell by means of two rounds of chromosome segregation preceded by a single round of DNA replication.Meiotic recombination,a hallmark of meiosis,is essential for faithful segregation of homologous chromosomes during the first meiotic cell division and enhances genetic diversity in gametes.This process begins with the formation of a large number of programmed DNA double strand breaks(DSBs)in germ cells which are subsequently repaired to generate either noncrossovers or crossovers.Thus,failures in meiotic recombination entail blockade in meiosis and sterility.Meiotic recombination relies on a large number of proteins including ssDNA-binding proteins to typically localize to DSBs as foci on meiotic chromosomes and then repair these DSBs.The resulting crossovers are critical for maintaining homolog interactions and lack of crossovers results in formation of univalent chromosomes,followed by chromosome mis-segregation and subsequent apoptosis of meiotic germ cells.Many meiosis-specific proteins have been studied genetically in model organisms from yeast to mouse.Moreover,mutations in several meiosis-specific genes have been found in humans with primary ovarian insufficiency or non-obstructive azoospermia.However,our understanding of their role in human meiosis is limited.MEIOB,an ssDNA-binding protein,is a meiosis-specific paralogue of RPA1 and exhibits3'–5'exonuclease activity.MEIOB forms a heterodimer with SPATA22 and the MEIOB/SPATA22 heterodimer interacts with the RPA heterotrimer.MEIOB and SPATA22 are dependent of each other and regulate early meiotic recombination.Here we report that the human infertility-associated missense mutation(N64I)in MEIOB causes protein degradation in mouse testes.In this study,we generated a mouse mutant to model the human MEIOB N64I mutation.The Meiob^N64I homozygous male mice have normal fertility and exhibit slight meiosis defects.It is possible that there are species-specific requirements for fertility.It is also possible that the species-specific protein sequence context modulates the functional consequences of the deleterious mutation.In addition,Meiob mutagenesis identifies serine 67as a critical residue for MEIOB.The Meiob^?S67/?S67 mutant mice are sterile and show a complete failure in DSBs repair in early meiotic recombination.Our biochemical studies reveal that the N64I and?S67 mutations cause self-aggregation of MEIOB and sharply reduced protein half-lives.Molecular genetic analyses of both point mutants reveal an important role for MEIOB in crossover formation in late meiotic recombination.Importantly,genetic studies of various combinations of Meiob mutant alleles(Meiob^N64I/N64I?Meiob ^N64I/-?Meiob ^N64I/?S67?Meiob^?S67/?S67),we find that the MEIOB protein levels are directly correlated with the severity of meiotic defects.Our results demonstrate that MEIOB regulates meiotic recombination in a dosage-dependent manner.