No abstract

Genetically modified animals are unique models with enormous scientific potential. Cryopreservation of pre-implantation embryos or of spermatozoa is a common approach to save those lines. The breeding of a line can be discontinued if a sufficient number of samples have been cryopreserved. To maintain the opportunity to recover a line, it is mandatory to assess the quality of the cryopreserved samples and to assure safe long-term storage conditions. Here, we investigated the revitalization rate of cryopreserved pre-implantation embryos stored in-house up to 158 months, of imported (and shipped) embryos, and of embryos received after in vitro fertilization. The storage period did not affect the revitalization rate, whereas the recovery of imported embryos was significantly reduced, possibly due to shipment conditions. The genotypes of genetically modified pups received following embryo-transfer were slightly smaller than expected by Mendelian laws. Intensive investigations of the hygienic state of the cryopreserved samples and the equipment used never showed microbiological contamination of a sample within a cryo-tube. However, environmental organisms were found frequently in the permanent freezers and dry shippers used. Since such contamination cannot be completely excluded and an embryo-transfer might not lead in all cases to a secure rederivation, foster mothers and revitalized pups should be housed in an intermediate facility and their health assessed before introducing them into the target facility.

Title: Genetically modified animals, in particular mice, are unique mutants with a major scientific potential. Cryopreservation of pre-implantation embryos or of spermatozoa is a common approach to protect those lines against loss or to archive them. Prerequisite to take a mutant line out of a breeding nucleus is the cryopreservation of a sufficient number of samples and a powerful quality assessment.Background: Several common protocols to cryopreserve spermatozoa and subsequently to forward these to an in vitro-fertilization under standardized conditions are published using donors of a strictly limited age-span. In practice, several limitations happen frequently for those approaches, e.g. the availability of genetically modified males, in particular if a line is in an experimental use or the mutation leads to restrictions. Female donors are often received from external sources and are subsequently not available before weaning. They are subject of several delays to induce an early superovulation. The aim of this report is to study the suitable age span of sperm and oocyte donors.