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Biochim Biophys Acta
2008 Mar 01;17783:717-28. doi: 10.1016/j.bbamem.2007.09.031.
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Tight junction biogenesis during early development.
Eckert JJ
,
Fleming TP
.
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The tight junction (TJ) is an essential component of the differentiated epithelial cell required for polarised transport and intercellular integrity and signalling. Whilst much can be learnt about how the TJ is constructed and maintained and how it functions using a wide range of cellular systems, the mechanisms of TJ biogenesis within developmental models must be studied to gain insight into this process as an integral part of epithelial differentiation. Here, we review TJ biogenesis in the early mammalian embryo, mainly considering the mouse but also including the human and other species, and, briefly, within the amphibian embryo. We relate TJ biogenesis to inherent mechanisms of cell differentiation and biosynthesis occurring during cleavage of the egg and the formation of the first epithelium. We also evaluate a wide range of exogenous cues, including cell-cell interactions, protein kinase C signalling, gap junctional communication, Na+/K+-ATPase and cellular energy status, that may contribute to TJ biogenesis in the embryo and how these may shape the pattern of early morphogenesis.
Fig. 1.
Blastocyst cavitation, tight junction formation and inner/outer cell orientation. (A) Schematic depicting inner cell mass (ICM) and trophectoderm (TE) cell lineages in early blastocysts and in re-cavitated isolated ICMs upon culture as well as additional primitive endoderm lineage in expanded blastocysts. (B) Bright field photograph of nascent mouse blastocyst before and (C) after differential labelling [172] to visualise inner cells (blue) and outer cells (red) by the fluorochromes, bisbenzimide and propidium iodide, respectively. (D, E) Confocal images of mouse blastocysts fixed and stained for TJ proteins, (D) showing a 3D projection demonstrating the belt-like distribution of ZO-2 and (E) a single slice midplane image showing apicolateral localisation of ZO-1α+ exclusively within the TE lineage. (F) Bright field picture and (G) single slice confocal image of a freshly isolated ICM fixed and stained negative for ZO-2. (H) Bright field image of a re-cavitated isolated ICM after 20 h of in vitro culture and (I) after differential labelling to visualise inner (blue) and outer (red) cells. (K) 3D projection of confocal slices taken from a re-cavitated cultured ICM fixed and stained showing the belt-like distribution of ZO-2 as an intact blastocyst.
Fig. 2.
Schematic overview of the major endogenous events associated with TJ biogenesis in mouse blastomeres over the 8- to 32-cell stages as they undergo differentiation into the trophectoderm epithelium. Top: embryo stages; lower: apicolateral regions of cell contact and the changing pattern of proteins assembled with respect to cell cycle. See text for further explanation and references of the maturation of the TJ domain.
