Effect of concanavalin A on the formation of the mouse blastocyst.

Culture of precompact zona-free mouse embryos in the plant lectin concanavalin A (Con A) at 20 micrograms/ml inhibits blastocyst formation. Cell division is retarded compared with control embryos, compaction of the morula is prevented, and fluid accumulation occurs within but not between cells. As little as two hours of incubation in Con A can cause developmental delay and an eventual increased incidence of lysis, and although embryos can recover from more prolonged pulses of Con A, the blastocysts formed are often abnormal. Blastocyst formation occurs in some embryos, but does not do so unless at least some cells have undergone a fifth round of cell division before incubation in the lectin. However, not all embryos that contained more than 32 cells compacted and showed intercellular fluid accumulation in Con A. Thus, blastocyst formation is not restricted solely by an inhibition of cell division or a reduction in cell number, but is also impaired by interference of the lectin with the cell surface and its interactions. Morulae bind divalent Con A and monovalent succinyl-Con A similarly, but developmental interference is absent with the latter, suggesting that divalent Con A acts through a cross-linking of surface receptors.