The usefulness of diploid/tetraploid embryo aggregation for facilitating xenogeneic embryo transfer between Mus musculus and Meriones unguiculatus

Abstract

The failure of interspecific embryo transfer between placental mammals is generally attributed to either some maternal immune response, failure of local immunoregulation, or failure of tissue interaction between trophectoderm (TE) and uterus at implantation. The objectives of this study were to develop technology for the production of interspecific diploid/tetraploid aggregate chimeras between Meriones unguiculatus (gerbil) and Mus musculus (mouse), and to use that technology to test the hypothesis that Mus musculus tetraploid embryos can support the fetal development of Meriones unguiculatus in the Mus musculus uterus. To develop methodology for the production and transfer of interspecific diploid/tetraploid aggregate chimeras, three areas were evaluated; 1. the use of rabbit antimurine whole serum antibody to immunosurgically isolate the Meriones unguiculatus inner cell mass (ICM), 2. the survival of Meriones unguiculatus blastocysts transferred to Mus musculus recipients and, 3. the implantation rates of Mus musculus tetraploid blastocysts transferred to Mus musculus recipients that were either 2.5 or 3.5 days post coitum (p.c ). The ICM of Meriones unguiculatus blastocysts were isolated by immunosurgery using rabbit antimurine whole serum. Meriones unguiculatus blastocysts did not survive to term in the Mus musculus uterus. Mus musculus tetraploid blastocysts transferred to Mus musculus recipients did not appear to demonstrate a statistically significant difference between recipients that were 2.5 or 3.5 days p.c. However, the implantation rates of those recipients that did contain implantation sites demonstrated a statistically significant (P<0.0005) higher rate of implantation in recipients that were 3.5 days p.c. Using the methodology developed and presented above, Mus musculus tetraploid 4-cell embryos were aggregated with either a Mus musculus or Meriones unguiculatus ICM, cultured 24 hours in vitro and aggregate blastocysts were transferred to 2.5 day p.c. Mus musculus recipients. One Mus musculus term fetus was produced from a diploid/tetraploid aggregate chimera, yet no Meriones unguiculatus term fetuses were produced. The survival of one intraspecific offspring demonstrates the tetraploid embryo's ability to establish and maintain the fetal-maternal interactions. However, the low rate of survival obtained in this study precludes conclusive assessment of the development of interspecific offspring by this procedure.