Expression of intercellular junctions during preimplantation development of the human embryo

A total of 74 human embryos were stained with gap junction proteinspecific anti-peptide antibodies and antibodies to the desmosomalprotein desmoplakin to reveal the expression pattern of intercellularjunctions during preimplantation development. Prior to implantation,the human embryo expresses predominantly connexin (Cx43)-containinggap junctions. Gap junctions were first detected in apposingcell membranes at the 4-cell stage and became increasingly organizedas development proceeded. In normal blastocysts, trophectoderm(TE) cells were linked by dense arrays of gap junctions whileinner cell mass (ICM) cells were linked by small, punctate gapjunctions. Gap junctions containing Cx32 or Cx26 were observedoccasionally in the TE of late blastocysts. Desmosomes appearedbetween outer cells prior to cavitation and were retained inthe TE, but not in the ICM. Levels of gap junction protein expressionwere variable in morphologically normal embryos at the samestage, suggesting that a normal appearance may not be a reliableindicator of future viability. Morphologically normal embryosoften possessed multinucleate, apoptotic and decompacting cells.They could show either extensive, disorganized over-expressionor reduced expression of gap junction protein. The results fitthe view that only embryos destined to survive display an organizedpattern of intercellular junctions. blastocyst/connexin/desmosome/gap junction/immunocytochemistry