Developmental fate and lineage commitment of singled mouse blastomeres

Abstract

SUMMARYThe inside-outside model has been invoked to explain cell-fate specification of the pre-implantation mammalian embryo. Here, we investigate whether cell-cell interaction can influence the fate specification of embryonic blastomeres by sequentially separating the blastomeres in two-cell stage mouse embryos and continuing separation after each cell division throughout pre-implantation development. This procedure eliminates information provided by cell-cell interaction and cell positioning. Gene expression profiles, polarity protein localization and functional tests of these separated blastomeres reveal that cell interactions, through cell position, influence the fate of the blastomere. Blastomeres, in the absence of cell contact and inner-outer positional information, have a unique pattern of gene expression that is characteristic of neither inner cell mass nor trophectoderm, but overall they have a tendency towards a 'trophectoderm-like' gene expression pattern and preferentially contribute to the trophectoderm lineage.

Dynamic transcriptional symmetry-breaking in pre-implantation mammalian embryo development revealed by single-cell RNA-seq

“…Despite the observed dynamic transcriptional symmetrybreaking during early embryo development, we would like to emphasize that even if a lineage specifier is asymmetrically distributed between early blastomeres, they could only 'guide', but not 'decide' the lineage track until other more definitive clues such as inner-outer position, cell polarity, cell-cell contacts (Lorthongpanich et al, 2012) emerge. However, once a blastomere has acquired dominant lineage specifiers (for example, Carm1) at the four-cell stage, the chance of keeping the dominant position in its daughter generation will be higher than those blastomeres with low level expression.…”

A molecular basis for developmental plasticity in early mammalian embryos

“…At around the 32-cell stage, when the cavity is clearly visible, cells that lie outside have a defined epithelial appearance and are apparently irreversibly determined to TE fate, whereas the cells that lie inside form the ICM. The segregation of TE and ICM fates requires cell-cell interactions, as recently shown in elegant experiments in which blastomeres were immediately separated after division for the first five division cycles of the embryo (Lorthongpanich et al, 2012). All resultant long-term separated blastomeres assumed a similar molecular identity that was distinct from both TE and ICM.…”

“…4A). The outer cells become polarised, with an asymmetric distribution of microvilli and organelles, whereas the inner cells remain apolar Lorthongpanich et al, 2012). All resultant long-term separated blastomeres assumed a similar molecular identity that was distinct from both TE and ICM.…”

Aneuploidy rates and blastocyst formation after biopsy of morulae and early blastocysts on day 5

“…Another potential argument against the practice of day 5 biopsy of non-expanded blastocysts is the concern that biopsy of early blastocysts or day 5 morulae may impair the allocation of cells to the inner cell mass and other aspects of cavitation, or remove post-differentied cells destined to become the inner cell mass. However, only cells from the periphery of the embryo are biopsied, and evidence supporting the inside outside and cell polarity models of lineage specification [15] suggest that even if biopsy occurs after differentiation, these cells are destined to become trophectoderm and not inner cell mass. However while this theory and our limited initial implantation and pregnancy outcomes are reassuring, these results must be confirmed in a prospective trial.…”