Expression of intercellular junctions during preimplantation development of the human embryo.

A total of 74 human embryos were stained with gap junction protein specific anti-peptide antibodies an antibodies to the desmosomal protein desmoplakin to reveal the expression pattern of intercellular junctions during preimplantation development. Prior to implantation, the human embryo expresses predominantly connexin (Cx43)-containing gap junctions. Gap junctions were first detected in apposing cell membranes at the 4-cell stage and became increasingly organized as development proceeded. In normal blastocysts, trophectoderm (TE) cells were linked by dense arrays of gap junctions while inner cell mass (ICM) cells were linked by small, punctate gap junctions. Gap junctions containing Cx32 or Cx26 were observed occasionally in the TE of late blastocysts. Desmosomes appeared between outer cells prior to cavitation and were retained in the TE, but not in the ICM. Levels of gap junction protein expression were variable in morphologically normal embryos at the same stage, suggesting that a normal appearance may not be a reliable indicator of future viability. Morphologically normal embryos often possessed multinucleate, apoptotic and decompacting cells. They could show either extensive, disorganized over-expression or reduced expression of gap junction protein. The results fit the view that only embryos destined to survive display an organized pattern of intercellular junctions.