title: Formation of functional tight junctions in Xenopus embryos.
abstract: Formation of the blastocoel in early Xenopus embryos was studied with a novel biotin-permeability assay and newly generated tight junction markers. The blastocoel forms at the first cleavage division since functional tight junctions which excluded biotin and established a segregated intraembryonic compartment were found at the 2-cell and all subsequent developmental stages. Unexpectedly, tight junctions before the 64-cell stage were not at their normal apical positions, but were found deep in the embryos, up to 200 micron from the apical surface. In these positions, the tight junctions left large areas of ion permeable lateral membranes exposed to the extraembryonic environment, explaining why electrophysiological experiments record a decrease in embryonic input resistances concomitant with early cleavage stages. Immunohistochemistry revealed that the recessed tight junctions did not influence the distribution of C-cadherin and Na+,K+ATPase. Both markers were present apical to recessed tight junctions, indicating that the maintenance of polarization of these basolateral markers does not require tight junctions. With further development, tight junctions assumed an increasingly apical location until, by the 2000-cell stage, they occupied their conventional positions between the blastomeres at the apical/lateral membrane boundaries.
authors.affiliation: Department of Cell Biology, Harvard Medical School, 220 Longwood Avenue, Boston, Massachusetts 02115, USA.
authors.forename: C S
authors.initials: CS
authors.lastname: Merzdorf
authors.forename: Y H
authors.initials: YH
authors.lastname: Chen
authors.forename: D A
authors.initials: DA
authors.lastname: Goodenough
mesh_terms: D000818:Animals; D001710:Biotin / Q000031:analogs & derivatives; D001755:Blastocyst / Q000737:chemistry / Q000166:cytology / Q000648:ultrastructure*; D015820:Cadherins / Q000032:analysis; D002463:Cell Membrane Permeability; D016764:Cell Polarity; D004625:Embryo, Nonmammalian / Q000737:chemistry / Q000166:cytology / Q000648:ultrastructure*; D005455:Fluorescent Antibody Technique; D015151:Immunoblotting; D008565:Membrane Proteins / Q000032:analysis; D008854:Microscopy, Electron; D062793:Occludin; D010063:Ovum / Q000737:chemistry; D010750:Phosphoproteins / Q000032:analysis; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis; D013388:Succinimides; D019108:Tight Junctions / Q000502:physiology / Q000648:ultrastructure*; D029867:Xenopus Proteins; D014982:Xenopus laevis; D062826:Zonula Occludens-1 Protein
chemical_list: D015820:Cadherins; D008565:Membrane Proteins; D062793:Occludin; D010750:Phosphoproteins; D013388:Succinimides; C569045:TJP1 protein, Xenopus; D029867:Xenopus Proteins; D062826:Zonula Occludens-1 Protein; C061443:sulfosuccinimidyl 6-(biotinamido)hexanoate; D001710:Biotin; D000254:Sodium-Potassium-Exchanging ATPase