Magic embryology: how the placenta appears (Introduction)

by David Turell , Sunday, October 25, 2020, 18:13 (1491 days ago) @ David Turell

More on the genetics and stem cell changes:

https://www.nature.com/articles/d41586-020-02914-0

"The placenta is a defining feature of being a mammal, and its formation is one of the first steps in mammalian development. The embryo begins to make its placenta without direct guidance from its mother — rather, it follows a set of molecularly encoded, do-it-yourself assembly instructions. (my bold)

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"...studies established that the ball-shaped mouse embryo develops an external ‘rind’ of cells fated to become placenta about three days after fertilization. These cells, called the trophectoderm, encircle a group of inner cells that are considered pluripotent — they possess the capacity to produce all cell types of the body, [ i.e., stem cells]

"In mouse embryos, this first cellular differentiation involves the polarization of trophectoderm cells along one axis, known as the apical–basal axis. Cell-polarity proteins accumulate on the apical side of trophectoderm cells, repressing signalling through the HIPPO pathway. By contrast, HIPPO signalling is active in the pluripotent cells, because they are unpolarized. In the pluripotent cells, HIPPO signalling prevents the transcription factor YAP1 from moving to the nucleus. In trophectoderm cells, nuclear YAP1 promotes the expression of the trophectoderm genes Cdx2 and Gata3, and represses the pluripotency gene Sox2

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"...the authors analysed gene expression in human and cow embryos, and demonstrated that YAP1 localization and GATA3 gene expression are conserved between species as the trophectoderm emerges. Next, they disrupted cell polarization in each species by inhibiting atypical protein kinase C (aPKC), a key polarization protein. This prevented nuclear localization of YAP1, and disrupted GATA3 expression. These observations point to a conserved gene-regulatory module that governs the first cell-fate decision in mouse, cow and human embryos

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"Discoveries in mouse and human embryos contribute directly to our understanding of stem-cell biology. Cultured stem cells were first derived from both pluripotent and trophectoderm cells of the mouse embryo, paving the way for the establishment of stem-cell lines from human embryos."

Comment: Note the reference to informative instructions in my bold in the first paragraph. Only a designer could supply them