Mummichog gill and operculum exhibit functionally consistent claudin-10 paralog profiles and Claudin-10c hypersaline...

Area of Science:

• Molecular Biology
• Comparative Physiology
• Environmental Adaptation

Background:

• Tight junction (TJ) proteins, specifically Claudin (Cldn)-10, are implicated in the sodium (Na+) secretion pathway in hyposmoregulating fish.
• Understanding the role of Cldn-10 in branchial epithelia is key to explaining how fish adapt to hypersaline environments.

Purpose of the Study:

• To investigate the expression, localization, and post-translational modification of Cldn-10 proteins in the gill and opercular epithelium (OE) of mummichogs (Fundulus heteroclitus).
• To determine the functional role of Cldn-10 in salinity adaptation and Na+ secretion under hypersaline conditions.

Main Methods:

• Organ-specific transcript analysis to identify cldn-10 paralog expression.
• Western blot analysis and glycosidase treatment to examine Cldn-10c protein abundance and modifications.
• Immunofluorescence microscopy to determine the cellular localization of Cldn-10c in gill and OE ionocytes.

Main Results:

• Abundant cldn-10 paralog transcripts were found in branchial organs, increasing after hypersaline challenge.
• Cldn-10c exists as a glycosylated form and its protein abundance increases in the gill and OE of fish exposed to hypersaline water.
• Cldn-10c localizes to the apical crypts of ionocytes and partially colocalizes with CFTR and F-actin, consistent with TJ localization.

Conclusions:

• Claudin-10c plays a significant role in the salinity-responsive Na+ secretion pathway in mummichog branchial epithelia.
• The observed changes in Cldn-10c expression, modification, and localization support its function in maintaining ion balance in hyperosmotic environments.