Publications (3)7.83 Total impact
Chapter: Tight Junctions during Development[Show abstract] [Hide abstract]
ABSTRACT: During early development, tight junction biogenesis and the differentiation of the first epithelium in the blastocyst is critical for embryonic patterning and organization. Here, we discuss the programme of exactly timed transcription, translation, and post-translational modification of specific junctional proteins that regulates the stepwise membrane assembly of tight junctions during cleavage in the mouse model. Underlying mechanisms that coordinate these processes are discussed along with newly emerging data from other mammalian species. In the mouse embryo, junction assembly follows the establishment of cell polarity at the 8-cell stage and is characterized by sequential membrane delivery of JAM-1, ZO-1α− and Rab13, cingulin and ZO-2 followed by ZO-1α+ and occludin. Tight junction assembly occurs over three developmental stages; compaction, first differentiative division and cavitation. Post-translational modification of occludin, the late expression of ZO-1α+ isoform and their intracellular colocalisation may all contribute to the rapid coordinated delivery of these two proteins to the membrane, resulting in the final sealing of the tight junction followed by blastocoel cavitation. This coordinated delivery of these two tight junction-associated proteins may therefore provide a rate limiting step for the sealing of tight junctions and regulated timing of blastocoel cavitation. Taken together, our studies in mouse, human and bovine embryos suggest that defects in the tightly controlled programming of early development may contribute to reduced embryo viability.
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ABSTRACT: We have investigated the contribution of the tight junction (TJ) transmembrane protein junction-adhesion-molecule 1 (JAM-1) to trophectoderm epithelial differentiation in the mouse embryo. JAM-1-encoding mRNA is expressed early from the embryonic genome and is detectable as protein from the eight-cell stage. Immunofluorescence confocal analysis of staged embryos and synchronized cell clusters revealed JAM-1 recruitment to cell contact sites occurred predominantly during the first hour after division to the eight-cell stage, earlier than any other TJ protein analysed to date in this model and before E-cadherin adhesion and cell polarization. During embryo compaction later in the fourth cell cycle, JAM-1 localized transiently yet precisely to the apical microvillous pole, where protein kinase Czeta (PKCzeta) and PKCdelta are also found, indicating a role in cell surface reorganization and polarization. Subsequently, in morulae and blastocysts, JAM-1 is distributed ubiquitously at cell contact sites within the embryo but is concentrated within the trophectoderm apicolateral junctional complex, a pattern resembling that of E-cadherin and nectin-2. However, treatment of embryos with anti-JAM-1-neutralizing antibodies indicated that JAM-1 did not contribute to global embryo compaction and adhesion but rather regulated the timing of blastocoel cavity formation dependent upon establishment of the trophectoderm TJ paracellular seal.
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ABSTRACT: During early development, the eutherian mammalian embryo forms a blastocyst comprising an outer trophectoderm epithelium and enclosed inner cell mass (ICM). The short-term goal of blastocyst morphogenesis, including epithelial differentiation and segregation of the ICM, is mainly regulated autonomously and comprises a combination of temporally controlled gene expression, cell polarisation, differentiative cell divisions and cell-cell interactions. This aspect of blastocyst biogenesis is reviewed, focusing, in particular, on the maturation and role of cell adhesion systems. Early embryos are also sensitive to their environment, which can affect their developmental potential in diverse ways and may lead to long-term consequences relating to fetal or postnatal growth and physiology. Some current concepts of embryo-environment interactions, which may impact on future health, are also reviewed.