Individual blastomeres of 16- and 32-cell mouse embryos are able to develop into foetuses and mice

Abstract

Cell and developmental studies have clarified how, by the time of implantation, the mouse embryo forms three primary cell lineages: epiblast (EPI), primitive endoderm (PE), and trophectoderm (TE). However, it still remains unknown when cells allocated to these three lineages become determined in their developmental fate. To address this question, we studied the developmental potential of single blastomeres derived from 16- and 32-cell stage embryos and supported by carrier, tetraploid blastomeres. We were able to generate singletons, identical twins, triplets, and quadruplets from individual inner and outer cells of 16-cell embryos and, sporadically, foetuses from single cells of 32-cell embryos. The use of embryos constitutively expressing GFP as the donors of single diploid blastomeres enabled us to identify their cell progeny in the constructed 2n↔4n blastocysts. We showed that the descendants of donor blastomeres were able to locate themselves in all three first cell lineages, i.e., epiblast, primitive endoderm, and trophectoderm. In addition, the application of Cdx2 and Gata4 markers for trophectoderm and primitive endoderm, respectively, showed that the expression of these two genes in the descendants of donor blastomeres was either down- or up-regulated, depending on the cell lineage they happened to occupy. Thus, our results demonstrate that up to the early blastocysts stage, the destiny of at least some blastomeres, although they have begun to express markers of different lineage, is still labile.

Totipotency: What It Is and What It Is Not

“…Similar results were obtained and similar conclusions were drawn from the observation that ''outer'' cells of human blastocysts form blastocyst-like structures that initiate expression of ICM-associated genes following reaggregation [38]. Finally, several authors [27,[39][40][41][42] have asserted that blastomeres isolated from morula-stage embryos are ''totipotent,'' because when they are reaggregated with tetraploid cells from a freshly dissociated embryo, either live-born animals or what appear to be normal blastocysts can be produced. Yet, there is no evidence in any of these studies that cells in the aggregate are ''totipotent'' in either sense of the term; that is, either able to produce all cells of the embryo or to organize these cells into a mature body.…”

A molecular basis for developmental plasticity in early mammalian embryos

“…Further experiments testing the potential of single blastomeres have been performed with tetraploid chimaeras, in which diploid cells are mixed with tetraploid cells and only the diploid cells contribute to the embryo. In these experiments, twins and multiplets from 2-, 4-, 8-and even 16-cell embryos have been reported (Tarkowski et al, 2001;Tarkowski et al, 2005;Tarkowski et al, 2010).The outcomes of these experiments (Fig. 3) rule out a strict early determination event during the first cleavages but they still allow for the existence of a 'bias' in the fate of the blastomeres (Bruce and Zernicka-Goetz, 2010), which is supported by quantitative analysis of the fate of different blastomeres at different stages (Piotrowska-Nitsche et al, 2005;Tabansky et al, 2013).…”

Embryo biopsy and development: the known and the unknown

“…This speculation is based on different studies showing that embryos at early stages of development (including at the 4-cell stage) are characterized by individual blastomeres that differ in their developmental fate and potency (PiotrowskaNitsche et al 2005, Tarkowski et al 2010, as well as in their transcriptomic profile and epigenetic features (Torres-Padilla et al 2007, Tang et al 2011. In this context, BB may be responsible for the embryo's adaptations that occurred as a consequence of blastomere/determinant removal.…”