title: Midblastula transition (MBT) of the cell cycles in the yolk and pigment granule-free translucent blastomeres obtained from centrifuged Xenopus embryos.
abstract: We obtained translucent blastomeres free of yolk and pigment granules from Xenopus embryos which had been centrifuged at the beginning of the 8-cell stage with cellular integrity. They divided synchronously regardless of their cell size until they had decreased to 37.5 microm in radius; those smaller than this critical size, however, divided asynchronously with cell cycle times inversely proportional to the square of the cell radius after midblastula transition (MBT). The length of the S phase was determined as the time during which nuclear DNA fluorescence increased in Hoechst-stained blastomeres. When the cell cycle time exceeded 45 min, S and M phases were lengthened; when the cell cycle times exceeded 70 min, the G2 phase appeared; and after cell cycle times became longer than 150 min, the G1 phase appeared. Lengths of G1, S and M phases increased linearly with increasing cell cycle time. Enhanced green fluorescent protein (EGFP)-tagged proliferating cell nuclear antigen (PCNA) expressed in the blastomeres appeared in the S phase nucleus, but suddenly dispersed into the cytoplasm at the M phase. The system developed in this study is useful for examining the cell cycle behavior of the cell cycle-regulating molecules in living Xenopus blastomeres by fluorescence microscopy in real time.
authors: Department of Biological Science, Faculty of Science, Yamaguchi University, 753-8512 Yamaguchi, Japan. iwao@yamaguchi-u.ac.jp
authors: Yasuhiro
authors: Y
authors: Iwao
authors: Yoshihisa
authors: Y
authors: Uchida
authors: Shuichi
authors: S
authors: Ueno
authors: Norio
authors: N
authors: Yoshizaki
authors: Yoshio
authors: Y
authors: Masui
mesh_terms: D000818:Animals; D001757:Blastomeres / Q000502:physiology* / Q000648:ultrastructure; D036703:Blastula / Q000166:cytology* / Q000502:physiology; D002453:Cell Cycle; D002467:Cell Nucleus / Q000235:genetics; D048429:Cell Size; D002498:Centrifugation; D004247:DNA / Q000032:analysis; D005260:Female; D008854:Microscopy, Electron; D018809:Proliferating Cell Nuclear Antigen / Q000235:genetics / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000502:physiology; D016196:S Phase; D013997:Time Factors; D014982:Xenopus laevis / Q000196:embryology*
chemical_list: D018809:Proliferating Cell Nuclear Antigen; D011993:Recombinant Fusion Proteins; D004247:DNA