Embryonic stem cells as models of trophoblast differentiation: progress, opportunities, and limitations

While the determination of the trophoblast lineage and the facilitation of placental morphogenesis by trophoblast interactions with other cells of the placenta are crucial components for the establishment of pregnancy, these processes are not tractable at the time of human implantation. Embryonic stem cells (ESCs) provide an embryonic surrogate to derive insights into these processes. In this review, we will summarize current paradigms which promote trophoblast differentiation from ESCs, and potential opportunities for their use to further define signals directing morphogenesis of the placenta following implantation of the embryo into the endometrium.

124 A THREE-DIMENSIONAL IN VITRO IMPLANTATION MODEL WITH NONHUMAN PRIMATE EMBRYOS AND EXTRACELLULAR MATRIX UNDER VARIOUS CULTURE CONDITIONS

The need for blastocyst culture and post-implantation embryo research has emerged in the past few years. Our objective is to evaluate a novel in vitro model to study implantation and placenta formation in vitro with rhesus macaque embryos under various culture conditions. A novel nonhuman primate in vitro 3-D system can provide cues for implantation and interaction with the extracellular environment not available in 2-D planar models. Optimization of such a model can be tested with diverse culture environments. We developed and evaluated an in vitro 3-D implantation model utilizing IVF-derived, blastocyst-stage rhesus macaque embryos embedded in 3-D Matrigel droplets cultured with different feeder cells and media. Signs of implantation including enlargement of the embryo mass, invasion and proliferation of trophectoderm cell layers, cystic formation, and cellular outgrowths derived from the embryo were initiated within the first week post-embedding. Trophoblast structures with protrusion and branches growing from the surface of embryo implants were observed. Immunohistochemical staining for chorionic gonadotropin (CG) combined with immunoassays for CG and progesterone indicated differentiation of trophoblastic cell lineages. In addition, we found morphological factors, such as proliferation of embryonic and extraembryonic structures, as well as initiation of protrusions interacting with the extracellular matrix, to predict successful establishment of prolonged embryo development. We further evaluated effects of different types of feeder cells and media combinations, and found that a combination of BRL, Ishikawa cells, and human uterine fibroblasts, provided an optimized culture microenvironment to promote peri-implantation embryo development and hormone secretion including CG and progesterone. In conclusion, we have established a 3-D in vitro system modeling implantation initiation, and demonstrating the capability of the embryo to interact with the extracellular matrix. Further studies will facilitate the methodology of peri-implantation blastocyst culture and accelerate our understanding of nonhuman primate embryo development, with potential for insights into early pregnancy loss and related pathologies. The present study and future directions may be extended to provide retrospective views on blastocyst selection for embryo transfer in assisted reproductive technology. This study was funded by NIH grants RR000167, RR21876, and HD053926.

Rhesus monkey placental transgene expression after lentiviral gene transfer into preimplantation embryos

Transgenic mice have provided invaluable information about gene function and regulation. However, because of marked differences between rodents and primates, some areas of human biology such as early embryonic development, aging, and maternal-fetal interactions would be best studied in a nonhuman primate model. Here, we report that gene transfer into rhesus monkey (Macaca mulatta) preimplantation embryos gives rise to transgenic placentas that express a reporter transgene (eGFP). Blastocysts resulting from culture of in vitro fertilized ova were transduced with a self-inactivating lentiviral vector and transferred into recipient females. One twin and one singleton pregnancy were produced from a single stimulation cycle, and one live rhesus monkey was born from each pregnancy. Placentas from all conceptuses showed expression of the transgene as detected by reverse transcription-PCR, ribonuclease protection assay, direct epifluorescence, immunohistochemistry, and Western blot analysis. Integration in somatic tissues of the offspring was not detected. A maternal immune response to the xenogeneic placental antigen was shown by the presence of anti-GFP antibodies in peripheral blood of the recipient females by day 99 of gestation (term = 165 days). These results demonstrate that transgene expression during gestation is compatible with successful pregnancy in nonhuman primates and provides an approach that could be broadly applicable to the development of novel models for primate biomedical research.