The hamster as a model for embryo implantation: insights into a multifaceted process

Abstract

Defects in preimplantation embryonic development, uterine receptivity, and implantation are the leading cause of infertility, pregnancy problems and birth defects. Significant progress has been made in our basic understanding of these processes using the mouse model, where implantation is ovarian estrogen-dependent in the presence of progesterone. However, an animal model where implantation is progesterone-dependent must also be studied to gain a full understanding of the embryo and uterine events that are required for implantation. In this regard, the hamster is a useful model and this review summarizes the information currently available regarding mechanisms involved in synchronous preimplantation embryo and uterine development for implantation in this species.

Figure 1. Membranous E-cadherin and F-actin localization in the morula and blastocyst stage embryos of hamsters

Arrowheads indicate E-cadherin (TRITC, red) and F-actin localization at cell-cell contact sites between blastomeres. A rat monoclonal E-cadherin antibody and Texas red-labeled phalloidin were used for E-cadherin and F-actin staining, respectively. Nuclei were stained with DAPI (blue). ICM, inner cell mass; TR, trophectoderm

Figure 2. Immunofluorescence of cytochrome P450 aromatase (Cyp19) protein in day 4 hamster blastocysts

Blastocysts of hamsters (a) and mice (c) were incubated with polyclonal anti-human aromatase antibody. As a negative control, hamster blastocysts (b) were stained without primary antibody. In comparison, mouse blastocysts (c) show no expression of Cyp19. Simultaneous staining was performed for Cyp19 antigen (TRITC, red) and nuclei (DAPI, blue). ICM, inner cell mass; TR, trophectoderm.

Figure 3. Implantation sites on days 4 and 5 of pregnancy as detected by intravenous injection of Chicago blue B dye injection

Blue bands along the uterine horn of hamsters (A, day 4 1200 h; B, day 4 1800 h; C, day 5 0900 h) and mice (D, day 5, 0800 h) are indicators of implantation sites.

Figure 4. MUC-1 immunostaining of the luminal epithelium of hamsters on days 1-5 of pregnancy

CT-1, a rabbit polyclonal antibody, was a generous gift from Dr. Daniel D. Carson, University of Delaware, DE, and used to detect MUC-1. CT-1 was the antibody of choice since it is not species specific nor affected by the glycosylation state of MUC-1 and recognizes all MUC-1 isoforms except the secreted form lacking the cytoplasmic tail. Immunostaining was performed using Zymed kit for rabbit primary antibody. Sections were lightly counterstained with hematoxylin. Arrows indicate apical MUC-1 staining. bl, blastocyst; ge, glandular epithelium; le, luminal epithelium; s, stroma.