BMP4 plays a role in apoptosis during human preimplantation development.

Comprehensive understanding of lineage differentiation and apoptosis processes is important to increase our knowledge of human preimplantation development in vitro. We know that BMP signaling is important for different processes during mammalian development. In mouse preimplantation embryos, BMP signaling has been shown to play a role in the differentiation into extra-embryonic trophectoderm (TE) and primitive endoderm (PE).

Expression of adhesion and extracellular matrix genes in human blastocysts upon attachment in a 2D co-culture system.

Study Question: What are the changes in human embryos, in terms of morphology and gene expression, upon attachment to endometrial epithelial cells?

Summary Answer: Apposition and adhesion of human blastocysts to endometrial epithelial cells are predominantly initiated at the embryonic pole and these steps are associated with changes in expression of adhesion and extracellular matrix (ECM) genes in the embryo.

What Is Known Already: Both human and murine embryos have been co-cultured with Ishikawa cells, although embryonic gene expression associated with attachment has not yet been investigated in an in vitro implantation model.

Study Design, Size, Duration: Vitrified human blastocysts were warmed and co-cultured for up to 48 h with Ishikawa cells, a model cell line for receptive endometrial epithelium.

Mitotic spindle disruption in human preimplantation embryos activates the spindle assembly checkpoint but not apoptosis until Day 5 of development.

Study Question: Is the spindle assembly checkpoint (SAC) active during human preimplantation development?

Summary Answer: Mitotic spindle disruption during mitosis activates the SAC from at least Day 3 of human preimplantation development, but this does not lead to apoptosis until Day 5.

What Is Known Already: Human preimplantation embryos frequently acquire chromosomal abnormalities, but the mechanisms behind this are poorly understood. It has been speculated that a dysfunctional SAC could be responsible.

Totipotency and lineage segregation in the human embryo.

During human preimplantation development the totipotent zygote divides and undergoes a number of changes that lead to the first lineage differentiation in the blastocyst displaying trophectoderm (TE) and inner cell mass (ICM) on Day 5. The TE is a differentiated epithelium needed for implantation and the ICM forms the embryo proper and serves as a source for pluripotent embryonic stem cells (ESCs). The blastocyst implants around Day 7.

Human trophectoderm cells are not yet committed.

Study Question: Are human trophectoderm (TE) cells committed or still able to develop into inner cell mass (ICM) cells?

Summary Answer: Human full blastocyst TE cells still have the capacity to develop into ICM cells expressing the pluripotency marker NANOG, thus they are not yet committed.

What Is Known Already: Human Day 5 full blastocyst TE cells express the pluripotency markers POU5F1, SOX2 and SALL4 as well as the TE markers HLA-G and KRT18 but not yet CDX2, therefore their developmental direction may not yet be definite.

Study Design, Size, Duration: The potency of human blastocyst TE cells was investigated by determining their in vitro capacity to develop into a blastocyst with ICM cells expressing NANOG; TE cells were isolated either by aspiration under visual control or after labeling with fluorescent 594-wheat germ agglutinin.