Stage‐Specific Expression and Perinuclear Enrichment of γ‐Tubulin During Tomont Development and Theront Morphogenesis in Cryptocaryon irritans

ABSTRACT

Cryptocaryon irritans is a lethal parasitic ciliate of marine fishes whose tomont stage is marked by repeated nuclear division and the morphogenesis of infective theronts, both dependent on dynamic microtubule reorganization. To investigate cytoskeleton‐associated regulation during this proliferative process, we cloned and characterized the γ‐tubulin gene ( Ci‐TUBG ) and γ‐tubulin complex protein 3 gene ( Ci‐TUBGCP3 ) from C. irritans . Sequence analysis showed that Ci‐TUBG contains a canonical dual tubulin domain architecture and is highly conserved relative to homologs from Ichthyophthirius multifiliis and Tetrahymena thermophila . Structural modeling and molecular docking suggested a stable putative interaction interface between Ci‐TUBG and Ci‐TUBGCP3. Spatiotemporal expression analysis and immunofluorescence revealed stage‐dependent upregulation and pronounced perinuclear enrichment of Ci‐TUBG during tomont division, with persistent perinuclear localization in theronts. RNA interference showed that Ci‐TUBG knockdown markedly reduced tomont hatching rate, decreased theront yield, and caused defects in theront morphogenesis accompanied by abnormal nuclear development. These findings indicate that Ci‐TUBG is essential for tomont division and theront morphogenesis in C. irritans and provide a basis for understanding cytoskeleton‐associated developmental regulation in this parasitic ciliate.