It may come as a surprise to learn that some new parents consume the placenta after birth, by processing it into capsules or cooking it. Other mammals do it too, for reasons that remain unclear. Regardless of one’s postpartum degustation choices, we can at least take solace in the fact that there’s a difference between the placenta and fetal tissue, although they arise from the same embryo.
But how are such cell-fate decisions made, and how do embryonic cells coordinate their choices among themselves? Cell fate is determined very early in embryonic development, even before the embryo gets implanted into the uterine wall. The prevailing theory of cell polarity proposes that cell fate is determined during cell division, by the asymmetric inheritance of cytoskeletal components that help to keep track of cell polarity.
In 2018, researchers from A*STAR’s Institute of Molecular and Cell Biology (IMCB) made an observation that suggested there might be other cytoskeletal components besides F-actin and microtubules that determine cell polarity during embryonic development.
Now, in their latest study published in Nature, an international team led by corresponding author Nicolas Plachta, a Senior Principal Investigator at IMCB, has discovered that keratin, a tough structural material that makes up hair and nails, is the only cytoplasmic intermediate filament that is expressed in the embryo during the preimplantation stage.
“Nobody knew exactly what keratin did in a developing embryo during preimplantation development,” said Plachta. “We discovered that keratins function as asymmetrically inherited factors specifying which cells of the embryo go on to be the precursor of the placenta.”
Using immunofluorescence imaging, the team studied the keratin subtypes in live mouse embryos that are predominantly expressed during the preimplantation stage. They observed that keratin filaments help in decision making by providing a memory of cell polarity: keratin filaments are inherited only by daughter cells that retain an outward face, suggesting that they serve as a physical memory of apical-basal polarity.
“The discovery that keratins function as symmetrically inherited fate determinants provides a mechanism to understand how embryonic cell lineage fate is influenced at cell divisions during the early stage of development,” said Plachta. “This extends the idea that the fate of early blastomeres is predictable and validates a key aspect of the cell-polarity model.”
The A*STAR-affiliated researchers contributing to this research are from the Institute of Molecular and Cell Biology (IMCB) .