Embryo transfer (ET) is a key procedure related to assisted reproductive technologies (ART) in mice. The success of other gamete manipulation in vitro techniques and their efficiency need to be confirmed with their in vivo developmental competency, evidenced by the ability to produce a successful pregnancy after embryo transfer. Depending on the ARTs used, the number of embryos transferred into the oviduct between 8–12 is generally used in IVF and ICSI seems to produce a higher success rate measured as the ratio between the number of embryos transferred and the number of pups born. However, a higher number is required for advanced engineering such as SCNT, which usually has a lower pups rate.
ICR breed mouse is generally used to be the surrogate and foster mother, as the estrous cycle can be easily detected through visual observation of the vaginal mucosa. The synchronization between the day of in vitro fertilization and the pseudopregnancy generation of the surrogate mother is required before doing ET. Pseudopregnancy can be induced by mating an estrous ICR female mouse with a vasectomized male mouse on the day of in vitro fertilization; female receptivity to the male is higher at proestrus (usually at 5 pm on the day of IVF/ICSI/SCNT). The vaginal plug must be checked the next day (usually at 9 am) to confirm that the mating was successful and the female is in the stage of pseudopregnancy. On this day, the embryo generated from ARTs has been at the 2-cell stage, which is ready for transplantation.
However, there are two different methods of ET, which are the 2-cell stage and the morula/blastocyst stage. ET at the 2-cell stage is performed on the 2nd day of ARTs or on the day of vaginal plug confirmation of the pseudopregnancy mouse (0.5 dpc); the embryos are transplanted into the oviduct.
Meanwhile, the morula or blastocyst stage of ET is usually performed 3 or 4 days after creating a pseudopregnant mouse (~3.5 days post coitum/dpc). At this stage, embryos usually enter the uterus, so ET is done by placing the embryo in that area.
The following are my documentation in doing ET. At least 60% pups rate is obtained from IVF or ICSI.
The photos and illustration are personal documentation.
