Cldn18 evolution reveals pleiotropic constraints in vertebrate stomach loss

Claudin 18 evolved in jawed vertebrates and its loss correlates with stomach reduction, constrained by its dual role in gastric and lung tissues across species.

• Why it matters: Understanding how pleiotropic genes influence anatomical innovations and losses helps clarify the constraints shaping vertebrate evolution and phenotypic diversity.
• What they did: The study analyzed CLDN18 across jawed vertebrates, revealing its origin in the gnathostome ancestor, its expression in stomachs of elasmobranchs, and its absence in agastric lineages like chimaeras and lungfishes, with detailed exon architecture analysis.
• The result: Findings show gene loss, tissue-specific regulation, and exon modifications driven by pleiotropy, illustrating how these factors have constrained stomach evolution and shaped epithelial diversity in vertebrates.