title: Plasma membrane regionalization and compaction of mouse cleaving embryos: effect of microtubule and microfilament inhibitors.
abstract: Two-cell embryos were incubated during 44 h in media containing either microtubule or microfilament inhibitors. The lowest doses that inhibit cleavage were found to be 0.5 micrograms/ml for colchicine and colcemid, 5 micrograms/ml for cytochalasin B and 0.5 micrograms/ml for cytochalasin D. After incubation with the minimal doses of these drugs, embryos were either fixed immediately or transferred to fresh media without drugs and cultured for different times before fixation. Then, embryos were processed for scanning electron microscopy. Following incubation with microtubule inhibitors, less than 10% of the embryos were compacted and about 20% became so in fresh medium. Regionalization was revealed by the cytochemical demonstration of alkaline phosphatase or 5'-nucleotidase on the apposing surfaces of blastomeres in 50% of the embryos, including all those that were compacted. By scanning microscopy microvilli were seen evenly distributed on the embryo surface, as they are observed in normal 2-cell embryos. Following incubation with microfilament inhibitors, few embryos were compacted and about 90% compacted within 4 h in fresh medium. Alkaline phosphatase activity was detected between blastomeres in all compacted embryos and in one half of those still uncompacted. Scanning microscopy showed patches of microvilli on the outer surface which had become otherwise smooth. During incubation in fresh medium, microvilli concentrated in two large patches placed at the antipodes of the embryo. From these results we conclude that cytokineses is not required for cell membrane regionalization, that blastomeres regionalize before they compact, that microtubule and microfilament inhibitors affect differently the array of microvilli on the external surface of arrested embryos.
mesh_terms: D015720:5'-Nucleotidase; D000469:Alkaline Phosphatase / Q000032:analysis; D000818:Animals; D002970:Cleavage Stage, Ovum / Q000201:enzymology / Q000648:ultrastructure*; D003078:Colchicine / Q000494:pharmacology; D003599:Cytoskeleton / Q000187:drug effects* / Q000648:ultrastructure; D051379:Mice; D008854:Microscopy, Electron; D008870:Microtubules / Q000187:drug effects*; D008871:Microvilli / Q000187:drug effects; D009708:Nucleotidases / Q000032:analysis
chemical_list: D009708:Nucleotidases; D000469:Alkaline Phosphatase; D015720:5'-Nucleotidase; D003078:Colchicine