Immunocytochemical studies of the interactions of cadherins and catenins in the early Xenopus embryo.
Linkage of cadherins to the cytoskeleton is crucial for their adhesive function. Since alpha- and beta-catenin play a key role in this linkage, these proteins are possible targets for processes that control cell-cell adhesion. To achieve a better understanding of the regulation of cell-cell adhesion in embryonic morphogenesis, we used immunohistology to investigate how in Xenopus blastomeres catenins respond to disturbances in the expression of maternal cadherins. Overexpression of myc-tagged maternal cadherin leads to a proportionate increase of the level of beta-catenin. The two proteins colocalize in the endoplasmic reticulum, in cytoplasmic vesicles, and along the cell membrane, indicating that the beta-catenin binds to overexpressed cadherin early in its passage to the plasma membrane. Expression of cadherin is essential for the stable presence of beta-catenin, as depletion from maternal cadherin mRNA leads to a complete loss of beta-catenin from the blastomeres. alpha-Catenin behaves differently. Overexpression of cadherin leaves the amount and localization of alpha-catenin largely unaffected, and additional cadherin inserts itself into the membrane without a proportionate rise in the level of membrane-bound alpha-catenin. However, cadherin mRNA depletion leads to a redistribution of alpha-catenin from the membrane to the cytoplasm. Thus, cadherin is required to localize alpha-catenin to the membrane, but the amount of alpha-catenin along the membrane seems to be restricted to a certain level which cannot be exceeded. The relevance of these observations for the regulation of cadherin-mediated cell adhesion in the Xenopus embryo is discussed. Additionally, we demonstrate that plakoglobin, like beta-catenin an armadillo repeat protein, shows neither accumulation after overexpression nor colocalization with the overexpressed cadherin.
Kurth
T
T
Max-Planck-Institut für Entwicklungsbiologie, Abteilung Zellbiologie, Tübingen, Germany.
Fesenko
I V
IV
Schneider
S
S
Münchberg
F E
FE
Joos
T O
TO
Spieker
T P
TP
Hausen
P
P
D000818:Animals; D015820:Cadherins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D051180:Desmoplakins; D019084:Fluorescent Antibody Technique, Indirect; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators; D029867:Xenopus Proteins; D014982:Xenopus laevis / Q000196:embryology; D051178:alpha Catenin; D051176:beta Catenin; D051185:gamma Catenin
C495266:CTNNB1 protein, Xenopus; D015820:Cadherins; D003598:Cytoskeletal Proteins; D051180:Desmoplakins; D016271:Proto-Oncogene Proteins c-myc; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; D029867:Xenopus Proteins; D051178:alpha Catenin; D051176:beta Catenin; D051185:gamma Catenin