Developmental Bias in Cleavage-Stage Mouse Blastomeres

Abstract

Summary Introduction The cleavage stage mouse embryo is composed of superficially equivalent blastomeres that will generate both the embryonic inner cell mass (ICM) and the supportive trophectoderm (TE). However, it remains unsettled whether the contribution of each blastomere to these two lineages can be accounted for by chance. Addressing the question of blastomere cell fate may be of practical importance, as preimplantation genetic diagnosis (PGD) requires removal of blastomeres from the early human embryo. To determine if blastomere allocation to the two earliest lineages is random, we developed and utilized a recombination-mediated, non-invasive combinatorial fluorescent labeling method for embryonic lineage tracing. Results When we induced recombination at cleavage stages, we observed a statistically significant bias in the contribution of the resulting labeled clones to the trophectoderm or the inner cell mass in a subset of embryos. Surprisingly, we did not find a correlation between localization of clones in the embryonic and abembryonic hemispheres of the late blastocyst and their allocation to the TE and ICM, suggesting that TE-ICM bias arises separately from embryonic-abembryonic bias. Rainbow lineage tracing also allowed us to demonstrate that the bias observed in the blastocyst persists into post-implantation stages, and therefore has relevance for subsequent development. Discussion The Rainbow transgenic mice that we describe here have allowed us to detect lineage-dependent bias in early development. They should also enable assessment of the developmental equivalence of mammalian progenitor cells in a variety of tissues.

Heterogeneity in Oct4 and Sox2 Targets Biases Cell Fate in 4-Cell Mouse Embryos

“…Approaching these questions has been difficult because of the inherent developmental flexibility of the embryo and because of previous technical limitations that prevented accurate quantification of gene expression levels in individual cells as development progresses. Although it has previously been thought that cells are homogenous until generation of inside and outside cells, more recent studies have opened a new possibility that cells at the 4-cell stage can already exhibit differences in cell fate Tabansky et al, 2013) and developmental potential (Morris et al, 2012;. This led to the suggestion that the differential activity of epigenetic regulators such as CARM1 (Torres-Padilla et al, 2007) or PRDM14 (Burton et al, 2013), or the differential behavior of transcription factors such as Oct4 (Plachta et al, 2011), at the 4-cell stage could be linked to differential cell fate and potential.…”

“…Sox21 mRNA Expression Is Highly Variable at the 4-Cell Stage and Correlates with the Expression of Pluripotency-Related Genes We reasoned that highly heterogeneous genes in the 4-cell embryo were of particular interest as cells at this stage can display differential fate Bischoff et al, 2008;Plachta et al, 2011;Tabansky et al, 2013) and potential Morris et al, 2012). One of the most highly heterogeneous genes in all embryos analyzed at the 4-cell stage is the gene encoding the transcription factor Sox21 (Figure 2A), which is involved in regulating ES cell-fate downstream of Sox2 (Kuzmichev et al, 2012;Mallanna et al, 2010).…”

“…Historically, cells of the early mouse embryo were considered identical in their ability to give rise to embryonic or extra-embryonic lineages, due to the regulative ability of the embryo to compensate for alterations in cell arrangement (Hillman et al, 1972;Tarkowski, 1959). However, more recent evidence has suggested that cells as early as the 4-cell stage become heterogeneous, exhibiting differences in developmental fate and potential (Bischoff et al, 2008;Tabansky et al, 2013) and in the activity of specific cell-fate regulators (Burton et al, 2013;Plachta et al, 2011;Torres-Padilla et al, 2007). This heterogeneity indicates the possibility that the breaking of embryo symmetry starts earlier than expected, prior to differences in cell position and polarity evident from the 16-cell-stage onward (Fleming, 1987;Johnson and Ziomek, 1981).…”

Origin of cellular asymmetries in the pre-implantation mouse embryo: a hypothesis

“…For example, the orientation and the order of cell division from the 2-to the 4-cell stage influence the fate of a blastomere [11]. individuals that will contribute either to ICM or TE, in a significant number of embryos [12].…”

Totipotency: What It Is and What It Is Not

“…Rather it suggests that the distinction between regulative and mosaic development is a false dichotomy [159]. Cell fate decisions are produced by a continuum of overlapping and redundant mechanisms [76], with oocyte-derived factors clearly playing a critical role in the developmental competency of early blastomeres [160][161][162][163][164].…”