Littermate influence on infant growth in mice: comparison of SJL/J and ICR as cotransferred carrier embryos

Improvement of short straws for sperm cryopreservation: installing an air-permeable filter facilitates handling

Saving space for sperm cryopreservation would aid mouse genetics research. We previously developed the ST (sperm freezing in ShorT STraw to reduce STorage space) method for cryopreserving mouse sperm in a smaller storage space than conventional methods. However, our ST method has two drawbacks: difficulties during freeze-thaw procedures and the potential risk of sperm loss during storage. Here, we refine ST, terming the new method improved ST (iST). In iST, the straw has an air-permeable filter and the straw container (2-ml cryotube) is endowed with air vents. As in our ST method, iST frozen-thawed sperm showed good performance upon in vitro fertilization. Moreover, up to nine straws can be stored in one cryotube, occupying less storage space than conventional methods. This method provides an easy and space-saving cryopreservation method for mouse sperm, and thus will be valuable for mouse genetics researchers.

Freezing sperm in short straws reduces storage space and allows transport in dry ice

Efficient cryopreservation and transportation of mouse sperm are among the most desirable strategies for current and future research on mouse genetics. However, the current method for sperm cryopreservation uses an 11-cm plastic straw, which is a bulky and fragile container. Developing an alternative to overcome the limitations associated with this method would accelerate biomedical research. Here, we developed the ST (sperm-freezing in ShorT STraw to reduce STorage space) method for cryopreserving mouse sperm in short 3.8-cm plastic straws. Up to nine short straws can be stored in a cryotube, reducing storage space. We further show that sperm frozen by the ST method can be transported in liquid nitrogen or dry ice without any detrimental effects on subsequent fertilization and the birth rate. Our findings suggest that this sperm-freezing method is beneficial not only for individual laboratories but also for large-scale mutagenesis/knockout and phenotyping programs.

Maternal prolactin during late pregnancy is important in generating nurturing behavior in the offspring

Although maternal nurturing behavior is extremely important for the preservation of a species, our knowledge of the biological underpinnings of these behaviors is insufficient. Here we show that the degree of a mother's nurturing behavior is regulated by factors present during her own fetal development. We found that Cin85-deficient (Cin85^-/-) mother mice had reduced pituitary hormone prolactin (PRL) secretion as a result of excessive dopamine signaling in the brain. Their offspring matured normally and produced their own pups; however, nurturing behaviors such as pup retrieval and nursing were strongly inhibited. Surprisingly, when WT embryos were transplanted into the fallopian tubes of Cin85^-/- mice, they also exhibited inhibited nurturing behavior as adults. Conversely, when Cin85^-/- embryos were transplanted into the fallopian tubes of WT mice, the resultant pups exhibited normal nurturing behaviors as adults. When PRL was administered to Cin85^-/- mice during late pregnancy, a higher proportion of the resultant pups exhibited nurturing behaviors as adults. This correlates with our findings that neural circuitry associated with nurturing behaviors was less active in pups born to Cin85^-/- mothers, but PRL administration to mothers restored neural activity to normal levels. These results suggest that the prenatal period is extremely important in determining the expression of nurturing behaviors in the subsequent generation, and that maternal PRL is one of the critical factors for expression. In conclusion, perinatally secreted maternal PRL affects the expression of nurturing behaviors not only in a mother, but also in her pups when they have reached adulthood.