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The peri-implantation development involves zona escape (hatching) ofblastocysts and their attachment and proliferation. These events are difficultto study in vivo, so in this study hamster 8-cell embryos were cultured through the hatched and attached blastocyst stages usingdifferent formulations of hamster embryo culture medium (HECM)-2. Supplementation of succinate, amino acids, vitamins (inositol, pantothenate, choline chloride) and bovine serum albumin (BSA) to HECM-2 supported 100% development of zona-escaped blastocysts. In thismedium (designated as hatching, i.e. HECM-2h) all blastocysts invariablydeflated and escaped from focally lysed zonae, which underwent completedissolution. In their presence, pre-morula stage embryos also escaped fromzonae. Omission of BSA from HECM-2h failed to support zona escape whereas thatof vitamins reduced zona escape (34.0% 7.0). Blastocysts with the potential to undergo zona escape in HECM-2h were of high quality as they had ahigher mean cell number (MCN) than the MCN of those developing in BSA-freeHECM-2h (35.2 1.6 v. 24.3 1.1). Cell allocation (i.e. trophectoderm to innercell mass ratio) in blastocysts remained unaltered in both media (2.6 0.2 v.2.7 0.2). Supplementation of 10% bovine fetal serum (BFS) to HECM-2hwas detrimental to the development of blastocysts (22.3% 7.4) and noneof them underwent zona escape. Interestingly, BFS was required either as asupplement to the medium or as a coating on dishes for azonal blastocysts toattach (≥70%) and exhibit trophoblast (TB) outgrowth (30.3 ×10<emph type="7">3 2.9 × 10<emph type="7">3µm<emph type="7">2 at 48 h). These results show that HECM-2hsupports maximal development of zona-escaped blastocysts with the potential toattach and exhibit TB outgrowth, and there is a developmental stage-specificrequirement for serum during peri-attachment in hamster development. |
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