Formation of functional tight junctions in Xenopus embryos

Area of Science:

• Developmental Biology
• Cell Biology
• Embryology

Background:

• The blastocoel is a fluid-filled cavity crucial for early embryonic development.
• The precise timing and location of tight junction formation in Xenopus embryos are not fully understood.

Purpose of the Study:

• To investigate the formation and localization of tight junctions during early Xenopus development.
• To understand the functional implications of tight junction positioning on embryonic properties.

Main Methods:

• Utilized a novel biotin-permeability assay to assess barrier function.
• Employed newly generated tight junction markers for immunohistochemistry.
• Examined Xenopus embryos at various cleavage stages (2-cell to 2000-cell).

Main Results:

• Functional tight junctions, excluding biotin, were present from the 2-cell stage, segregating an intraembryonic compartment.
• Before the 64-cell stage, tight junctions were unusually recessed up to 200 microns from the apical surface.
• Recessed tight junctions did not affect the apical localization of C-cadherin and Na+,K+ATPase, indicating polarization is maintained independently.
• By the 2000-cell stage, tight junctions migrated to their conventional apical positions.

Conclusions:

• Blastocoel formation begins at the first cleavage division, established by early-forming tight junctions.
• The transient, recessed localization of tight junctions explains observed decreases in embryonic input resistance.
• Polarity of key basolateral markers is maintained independently of tight junction position during early Xenopus development.