title: Development of single mouse blastomeres enlarged to zygote size in conditions of nucleo-cytoplasmic synchrony.
abstract: The following blastomeres were enlarged to the size of the zygote by one, two or three rounds of blastomere enucleation and electrofusion: (1) from the 2-cell stage (referred to as 2/1 embryos), (2) from the 4-cell stage (referred to as 4/1 embryos), (3) from the 8-cell stage (referred to as 8/1 embryos). Such single enlarged blastomeres developed into blastocysts in vivo in 55.5% (2/1), 28% (4/1) and 6.6% (8/1) of cases. Their mean cell numbers were 45.3, 24.5 and 13.0 in 2/1, 4/1 and 8/1 embryos, respectively. When a blastomere nucleus from another mouse strain (heterologous nucleus) was substituted for a blastomere's own (homologous) one, then fewer blastocysts were formed from 2/1 embryos (34.6%), but not from 4/1 and 8/1 embryos. Five young (10.4%) were born from 2/1 embryos with a homologous nucleus, and nine (8.3%) from 2/1 embryos with heterologous nuclei. Four young (7.1%) were born from 4/1 embryos with heterologous nuclei. No young were obtained from 8/1 embryos. Incorrect cavitation resulting in trophoblastic vesicles and false blastocyst formation was common in 4/1 embryos (18.7% of those with homologous nuclei and 41.3% with heterologous nuclei) and in 8/1 embryos (53.3% and 43.7%, respectively). The results show that neither enlargement to zygote size nor nucleo-cytoplasmic synchrony improve postimplantation development of 4- and 8-cell stage blastomeres when compared with less enlarged non-synchronous ones; therefore, it appears that an insufficient number of inner cell mass cells in blastocysts and not too small a size of isolated blastomeres precludes their postimplantation development.
authors.affiliation: Department of Experimental Embryology, Institute of Genetics and Animal Breeding, Polish Academy of Sciences, Jastrzebiec, Wolka Kosowska, Poland.
authors.forename: Jacek A
authors.initials: JA
authors.lastname: Modliński
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Ozil
authors.forename: Marta K
authors.initials: MK
authors.lastname: Modlińska
authors.forename: Alina
authors.initials: A
authors.lastname: Szarska
authors.forename: Michael A
authors.initials: MA
authors.lastname: Reed
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Wagner
authors.forename: Jolanta
authors.initials: J
authors.lastname: Karasiewicz
mesh_terms: D000818:Animals; D001757:Blastomeres / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C