Stage‐specific response of preimplantation mouse embryos to W‐7, a calmodulin antagonist

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Abstract
Involvement of calmodulin‐dependent processes in preimplantation development of mouse embryos was studied with the use of N‐(6‐aminohexyl)‐5‐chloro‐1‐naohthalenesulfonamide (W‐7), a specific antagonist of calmodulin. At 25 μM, W‐7 interfered with compaction of eight‐cell embryos, caused decompaction of compacted eight‐cell embryos, inhibited cavitation of late morulae, and caused collapse and degeneration of blastocysts. These effects of W‐7 appear to be due to specific inhibition of calmodulin‐dependent processes, because W‐5, a less active analogue of W‐7, was less effective in interfering with development; at 25 μM, W‐5 had only a slight effect on compaction and had no effect on blastocyst formation, maintenance of blastocoels, or post‐blastocyst development. In addition to the developmental effects just described, W‐7 inhibited cell proliferation in four‐cell embryos and reduced cell numbers of morulae after treatment at the two‐ to eight‐cell stages. There was a marked increase in embryos' sensitivity to W‐7 at the late morula stage, and the sensitivity increased further as embryos developed into blastocysts; the effects of W‐7 were largely reversible after treatment at the two‐cell through the compacted eight‐cell stages, but not after treatment at the late morula or blastocyst stage. At the blastocyst stage, inner cell mass cells appeared to be slightly more resistant to W‐7 than trophectoderm cells. This differential sensitivity became more pronounced at the late blastocyst stage: after 3.5–4‐h exposure of late blastocysts to 25 μM W‐7, all trophectoderm cells degenerated but most of the inner cell masses survived. From these results it appears that calmodulin‐dependent processes are involved in development of mouse embryos at all of the preimplantation stages examined.