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During mouse preimplantation development, the components of the E-cadherin-catenin complex are derived from both maternal and zygotic gene activity and the adhesion complex is increasingly accumulated and stored in a nonfunctional form, ready to be used for compaction and the formation of the trophectoderm cell layer (Ohsugi et al., Dev. Dyn. 206:391–402, 1996). Here, we show that β-catenin is a major tyrosine-phosphorylated protein in oocytes and early cleavage-stage embryos and that the relative amount of phosphorylated β-catenin is greatly reduced during the morula-blastocyst transition. Peptide-specific antibodies indicate that β-catenin undergoes conformational changes and/or that the carboxy-terminal region of β-catenin is blocked during preimplantation development. Moreover, the availability of a carboxy-terminal epitope seems to depend on the tyrosine phosphorylation state of β-catenin and becomes unmasked when oocytes are treated with the tyrosine kinase inhibitor genistein. Our results suggest that tyrosine phosphorylation of β-catenin represents a molecular mechanism to keep the accumulating E-cadherin adhesion complex in a nonfunctional form. Dev Dyn 1999;216:168–176. © 1999 Wiley-Liss, Inc.

We have studied transcription, expression, and membrane localization of components of the E-cadherin-catenin complex stage by stage during mouse preimplantation development. Maternal E-cadherin and α- and β-catenin are stored as mRNA and/or protein in unfertilized eggs and are already assembled into a protein complex at this stage. After fertilization, it is likely that they mediate adhesion of early-stage blastomeres. Biosynthesis of plakoglobin is delayed relative to the other components. The temporal mRNA and protein expression patterns of the components of the cadherin-catenin complex correlate with the presence or absence of potential cytoplasmic polyadenylation elements (CPEs) in the 3′-UTRs of the respective cDNAs. Our results suggest that the components of the E-cadherin-catenin complex derived from both maternal and zygotic gene activity are increasingly accumulated and stored in a nonfunctional form during early cleavage stages and are ready to be used for compaction and the formation of the trophectodermal cell layer. © 1996 Wiley-Liss, Inc.

The cover shows a double immunofluorescence staining of ESAM-1 and PECAM-1 in the T cell zone of the peripheral lymph node of the mouse. Red immunofluorescence of ESAM-1 colocalizes with the bright green immunofluorescence of PECAM-1, resulting in the observed yellow immunofluorescence. Lymphatic endothelial cells express PECAM-1 but lack ESAM-1 and hence are manifested as dim green immunofluorescence. The image was taken from the article by Pfeiffer et al. ( pp. 2142–2155) in which the authors demonstrate that molecularly distinct cellular junctions of blood and lymphatic endothelial cells establish different functional barriers controlling the distribution antigens and immune cells in the peripheral lymph node.