SWR: an inbred strain suitable for generating transgenic mice

Production of fertilized oocytes and generation of transgenic mice is generally more efficient using F2 hybrid embryos than embryos from inbred mice. Most F2 hybrids are of the C57BL/6 background because of its genetic and embryologic features. However, our goal of developing a transgenic mouse model for rheumatoid arthritis necessitated using a susceptible mouse strain such as DBA/1. We prepared alpha and beta T-cell receptor (TCR) chain gene constructs and microinjected them into embryos from DBA/1, SWR, (DBA/1 x SWR)F1, and (SWR x DBA/1)F1 strains. We found SWR female mice to be prolific ovulators in response to exogenous hormones, with oocyte numbers comparable to those produced by (C57BL/6 x C3H)F1 female mice. Embryos from the (SWR x DBA/1)F1 or SWR strain were large and had prominent pronuclei, whereas (DBA/1 x SWR)F1 embryos were smaller and had less visible pronuclei, similar to those of DBA/1 embryos. Therefore, the pronuclear size and visibility are features of the SWR female mice and are independent of the genotype of the fertilizing spermatozoa. Resistance to lysis after co-injection of alpha beta TCR constructs and the efficiency of generating DNA-positive founders were comparable in SWR, (SWR x DBA/1)F1, and (C57BL6 x C3H)F2 embryos. Thus, the SWR mouse is another inbred strain, in addition to the FVB inbred strain, found to be highly suitable for propagation of transgenes. Furthermore, the SWR mouse is well defined genetically, and SWR females have a high ovulation rate, comparable to that of F1 hybrid mice.