The 2-cell block occurring during development of outbred mouse embryos is rescued by cytoplasmic factors present in inbred metaphase II oocytes
Short Communication | Published: 1 December 2008
Mario Zanoni1, Silvia Garagna1, Carlo A. Redi2 and Maurizio Zuccotti*,3
1Laboratorio di Biologia dello Sviluppo, Dipartimento di Biologia Animale and Centro di Ingegneria Tissutale, Universita' degli Studi di Pavia, Pavia, Italy, 2Fondazione I.R.C.C.S. Policlinico San Matteo, Pavia, Italy and 3Sezione di Istologia ed Embriologia, Dipartimento di Medicina Sperimentale, Universita’ degli Studi di Parma, Parma, Italy.
In mice, completion of preimplantation development in vitro is restricted to certain crosses between inbred strains. Most of the outbred and inbred strains cease development at the 2-cell stage, a phenomenon known as the "2-cell block". Reciprocal mating between blocking and non-blocking strains has shown that the 2-cell block is dependent upon female, but not male, developmental information. One question that still remains unanswered is whether the genome of the metaphase II (MII) oocyte is genetically programmed to express, during the very early stages of development, some factor(s) required to determine developmental competence beyond the 2-cell stage. In the present study, we have addressed this question by performing reciprocal MII-chromosome plate transfer between MII oocytes of a non-blocking inbred strain and MII oocytes of a blocking outbred strain. Here, we report that development beyond the 2-cell stage does not depend on the MII genome, but instead it relies on a cytoplasmic factor(s) already present in ovulated non-blocking oocytes, but absent, inactive or quantitatively insufficient in blocking oocytes. Further evidence of the ooplasmic origin of this component(s) was obtained by transferring a small quantity of ooplasm from non-blocking MII oocytes to blocking MII oocytes or 2-cell embryos. Following the transfer, a high percentage of blocking oocytes/embryos acquired developmental competence beyond the 2-cell stage and reached the blastocyst stage. This study shows that development beyond the 2-cell stage relies also on a factor(s) already present in the ovulated oocyte.
preimplantation, 2-cell block, nuclear transfer, cytoplasm transfer