Meiosis-specific cohesin component, Stag3 is essential for maintaining centromere chromatid cohesion, and required for DNA repair and synapsis between homologous chromosomes.

Cohesins are important for chromosome structure and chromosome segregation during mitosis and meiosis. Cohesins are composed of two structural maintenance of chromosomes (SMC1-SMC3) proteins that form a V-shaped heterodimer structure, which is bridged by a α-kleisin protein and a stromal antigen (STAG) protein. Previous studies in mouse have shown that there is one SMC1 protein (SMC1ß), two α-kleisins (RAD21L and REC8) and one STAG protein (STAG3) that are meiosis-specific. During meiosis, homologous chromosomes must recombine with one another in the context of a tripartite structure known as the synaptonemal complex (SC). From interaction studies, it has been shown that there are at least four meiosis-specific forms of cohesin, which together with the mitotic cohesin complex, are lateral components of the SC. STAG3 is the only meiosis-specific subunit that is represented within all four meiosis-specific cohesin complexes. In Stag3 mutant germ cells, the protein level of other meiosis-specific cohesin subunits (SMC1ß, RAD21L and REC8) is reduced, and their localization to chromosome axes is disrupted. In contrast, the mitotic cohesin complex remains intact and localizes robustly to the meiotic chromosome axes. The instability of meiosis-specific cohesins observed in Stag3 mutants results in aberrant DNA repair processes, and disruption of synapsis between homologous chromosomes. Furthermore, mutation of Stag3 results in perturbation of pericentromeric heterochromatin clustering, and disruption of centromere cohesion between sister chromatids during meiotic prophase. These defects result in early prophase I arrest and apoptosis in both male and female germ cells. The meiotic defects observed in Stag3 mutants are more severe when compared to single mutants for Smc1ß, Rec8 and Rad21l, however they are not as severe as the Rec8, Rad21l double mutants. Taken together, our study demonstrates that STAG3 is required for the stability of all meiosis-specific cohesin complexes. Furthermore, our data suggests that STAG3 is required for structural changes of chromosomes that mediate chromosome pairing and synapsis, DNA repair and progression of meiosis.

Frozen sperm as an alternative to shipping live mice.

Dissemination of live mice by air and/or ground shipping is costly and can result in spread of disease between senders' and recipients' colonies. Transporting cryopreserved sperm that can be recovered and used for deriving live mice by using assisted reproductive techniques may be a more economical, efficient, and safer alternative to shipping live animals. In this study, we tested the hypothesis that sperm cryopreserved at one location and then transported transcontinentally via a common package delivery service using both air and ground transport to a second location could be recovered for in vitro fertilization (IVF) to successfully derive liveborn offspring at the second location. Split aliquots of sperm from individual mice were tested at both senders' and recipients' locations by using similar cryopreservation and IVF procedures, in order to control for differences in handling procedures. At both senders' locations, fertilization rates using cryopreserved sperm were lower than those using fresh sperm. However, fertilization rates using sperm recovered after cryopreservation at the senders' locations were not significantly different than those obtained when the same cryopreserved sperm was recovered and used at the recipients' locations. At the one location where tested, the numbers of pups born and subsequently weaned after IVF using either shipped or nonshipped cryopreserved sperm were similar. We conclude that cryopreserved sperm can be transported between different facilities and used for IVF to successfully derive liveborn mice.