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.