Aquaporin splice variation differentially modulates channel function during marine teleost egg hydration

Area of Science:

• Marine biology
• Developmental biology
• Molecular genetics

Background:

• Aquaporin-mediated oocyte hydration is crucial for marine teleost early development and buoyancy.
• Teleost-specific aquaporin-1 cluster (TSA1C) genes and Ywhaz-like binding proteins co-evolved to regulate water channel trafficking.
• Understanding these mechanisms is key to comprehending early embryonic survival in marine environments.

Purpose of the Study:

• To investigate the role of intronic splice variants of Aqp1ab1 and Aqp1ab2 in regulating oocyte hydration in marine teleosts.
• To elucidate the mechanisms by which these variants inhibit or modulate canonical aquaporin function.
• To identify novel regulatory pathways controlling cell-surface expression and activity of water channels during oocyte hydration.

Main Methods:

• Analysis of in-frame intronic splice variants in Aqp1ab1 and Aqp1ab2 genes.
• Investigation of protein trafficking, hetero-oligomerization, and degradation pathways.
• Assessment of protein localization in the endoplasmic reticulum (ER) and oocyte plasma membrane.
• Quantification of Aqp1ab2 isoform expression ratios during oocyte hydration and channel recycling.

Main Results:

• In species with the full TSA1C, Aqp1ab1 intronic variants produce truncated proteins that inhibit canonical channel trafficking via ER retention and degradation.
• In species with only Aqp1ab2, variants (extended or truncated) enhance degradation and can partially reach the plasma membrane, inhibiting water flux.
• Expression ratios of inhibitory Aqp1ab2 isoforms are lowest during hydration and highest during canonical channel recycling, facilitating high water content in eggs.

Conclusions:

• Expression of inhibitory Aqp1ab1 and Aqp1ab2 isoforms represents a novel regulatory mechanism for oocyte hydration in marine teleosts.
• These variants modulate cell-surface expression and activity of canonical aquaporins.
• This regulatory system ensures optimal water content for early embryonic development and survival.