Increasing Oocyte Yield Through the Modification of Hormone Delivery

The McGill Integrated Core for Animal Modeling (MICAM) creates mouse disease models using CRISPR-Cas9 technology. A key step to generating genetically modified animal models is to produce fertilized oocytes. To obtain large numbers of oocytes, female mice must be superovulated by hormone injections. Typically, superovulation is induced by the administration of five international units (IU) of pregnant mare serum gonadotropin (PMSG) and five IU of human chorionic gonadotropin (hCG) by intraperitoneal (IP) injections 48 hours apart. However, a recent report has shown the administration of PMSG by subcutaneous (SC) injection results in a higher average yield of oocytes per mouse. This would allow the superovulation of fewer mice to generate the same number of oocytes, a key refinement to the process. This study split cohorts of female mice into two groups per injection session. Half of a cohort was given hormones using the standard superovulation regime, and half were given PMSG SC. Both cohorts were given hCG IP. On average, 23.58 oocytes were collected per female mouse given PMSG SC, while 16.43 oocytes were collected per female mouse given PMSG IP. This resulted in 7.15 more oocytes collected per female mouse administered PMSG SC rather than IP. For every three mice injected with PMSG IP, two females need to be injected with PMSG SC to collect the same number of oocytes. This study demonstrates that the administration of PMSG SC does result in the collection of more oocytes per mouse, reducing the number of female mice needed to be housed and superovulated.