Corujo-Simon E, Bates LE, Yanagida A, Jones K, Clark S, von Meyenn F, Reik W, Nichols J. Human trophectoderm becomes multi-layered by internalization at the polar region.
Dev Cell 2024;
59:2497-2505.e4. [PMID:
38889726 DOI:
10.1016/j.devcel.2024.05.028]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2023] [Revised: 02/02/2024] [Accepted: 05/24/2024] [Indexed: 06/20/2024]
Abstract
To implant in the uterus, mammalian embryos form blastocysts comprising trophectoderm (TE) surrounding an inner cell mass (ICM), confined to the polar region by the expanding blastocoel. The mode of implantation varies between species. Murine embryos maintain a single layered TE until they implant in the characteristic thick deciduum, whereas human blastocysts attach via polar TE directly to the uterine wall. Using immunofluorescence (IF) of rapidly isolated ICMs, blockade of RNA and protein synthesis in whole embryos, or 3D visualization of immunostained embryos, we provide evidence of multi-layering in human polar TE before implantation. This may be required for rapid uterine invasion to secure the developing human embryo and initiate formation of the placenta. Using sequential fluorescent labeling, we demonstrate that the majority of inner TE in human blastocysts arises from existing outer cells, with no evidence of conversion from the ICM in the context of the intact embryo.
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