Maternally and zygotically provided Cdx2 have novel and critical roles for early development of the mouse embryo

Abstract

Divisions of polarised blastomeres that allocate polar cells to outer and apolar cells to inner positions initiate the first cell fate decision in the mouse embryo. Subsequently, outer cells differentiate into trophectoderm while inner cells retain pluripotency to become inner cell mass (ICM) of the blastocyst. Elimination of zygotic expression of trophectoderm-specific transcription factor Cdx2 leads to defects in the maintenance of the blastocyst cavity, suggesting that it participates only in the late stage of trophectoderm formation. However, we now find that mouse embryos also have a maternally provided pool of Cdx2 mRNA. Moreover, depletion of both maternal and zygotic Cdx2 from immediately after fertilization by three independent approaches, dsRNAi, siRNAi and morpholino oligonucleotides, leads to developmental arrest at much earlier stages than expected from elimination of only zygotic Cdx2. This developmental arrest is associated with defects in cell polarisation, reflected by expression and localisation of cell polarity molecules such as Par3 and aPKC and cell compaction at the 8- and 16-cell stages. Cells deprived of Cdx2 show delayed development with increased cell cycle length, irregular cell division and increased incidence of apoptosis. Although some Cdx2-depleted embryos initiate cavitation, the cavity cannot be maintained. Furthermore, expression of trophectoderm-specific genes, Gata3 and Eomes, and also the trophectoderm-specific cytokeratin intermediate filament, recognised by Troma1, are greatly reduced or undetectable. Taken together, our results indicate that Cdx2 participates in two steps leading to trophectoderm specification: appropriate polarisation of blastomeres at the 8- and 16-cell stage and then the maintenance of trophectoderm lineage-specific differentiation.

CDX2 is essential for cell proliferation and polarity in porcine blastocysts

“…Our results, derived from CDX2-knockdown porcine embryos, indicate that CDX2 is not essential before blastocyst formation, since the siCDX2 blastocyst rate was no different from that of the control. This result is consistent with several studies in mice, which show that Cdx2-mutant or knockdown (Wu et al, 2010) embryos develop normally to the blastocyst stage; however, others have found that Cdx2 depletion induces developmental arrest before blastocyst formation (Jedrusik et al, 2010(Jedrusik et al, , 2015. Different time points for CDX2 accumulation in mice and other mammals might account for the different phenotypes of CDX2-depleted mouse and pig embryos.…”

“…Furthermore, Cdx2-deficient blastomeres allocate a normal number of cells to the TE in chimeric embryos (Ralston and Rossant, 2008). Despite using the same gene knockout and RNAi approaches, these results are directly contradictory to those reported in other studies, which have shown that Cdx2 depletion compromises cell polarity and induces developmental arrest before the blastocyst stage, as well as significantly reducing blastocyst rate (the ability of zygotes to normally develop into blastocysts) (Jedrusik et al, 2010(Jedrusik et al, , 2015. One plausible explanation for this discrepancy could be the different genetic backgrounds among strains.…”

“…In mice, both Cdx2-knockout and -knockdown blastocysts exhibit a hatching failure, decreased cell number, abnormal TE cell junctions/polarity and a disturbed TE GRN (Blij et al, 2012;Jedrusik et al, 2010Jedrusik et al, , 2015Nishioka et al, 2008;Ralston and Rossant, 2008;Strumpf et al, 2005;Wu et al, 2010). In primates (Sritanaudomchai et al, 2009) and cattle (Goissis and Cibelli, 2014;Madeja et al, 2013), CDX2 knockdown results in a hatching failure and deficient cell proliferation in blastocysts.…”

The effects of fertilization mode, embryo morphology at day 3, and female age on blastocyst formation and the clinical outcomes

“…Thus, the total blastocyst formation rate did not decrease significantly with the maternal age. However, older women may have abnormally low levels of stored maternally transcribed mRNA, which is involved in trophectoderm function and maintenance of the blastocoel [Jedrusik et al 2010]. That might explain the lower good-morphology blastocyst rate in older women [Harton et al 2013].…”

Causes and evolutionary consequences of primordial germ-cell specification mode in metazoans

“…1), the idea that localized maternal determinants are used in embryonic axial patterning remains controversial. For example, some studies, but not others, find evidence for a maternal role of gene products proposed to be maternal determinants (Cdx2) (55,56) in cell-fate specification in the embryo (57)(58)(59). Nevertheless, a significant body of data suggests that zygotic regulators and cell-cell interactions determine axis polarity and patterning in mammals (e.g., refs.…”