Molecular and functional characterization of septin 6 in rohu (Labeo rohita) reveals a strong immunopotentiating role and involvement in broad-spectrum disease protection.

Septins are cytoskeletal GTP-binding proteins engaged in cytokinesis, membrane remodelling, vesicular trafficking, and host-pathogen interactions. The ubiquitous distribution of septins and their role in immune defense in vertebrates indicate their potential practical applications. Although their biological importance is well recognized, the functional role of septins in immune defense, particularly septin 6 in Indian major carps and other fish species, remains poorly understood. The full-length septin 6 cDNA was successfully cloned from rohu (Labeo rohita) comprising a 1203 bp open reading frame, and the phylogenetic analysis showed strong sequence similarity with septin 6 of Anabarilius grahami (99 %). It was predominantly expressed in brain, spleen, heart and gills, and during the early developmental stages. Its transcriptional expression was significantly enhanced in three pathogen models, Argulus siamensis, poly I:C, and Aeromonas hydrophila, indicating a potential role in immune defense. The intraperitoneal exposure of recombinant protein of septin 6 (~46 kDa) in rohu modulated the expression of immune-linked genes. Furthermore, in vivo experiments demonstrated a strong protective immunity, with 91 % relative percentage survival against A. hydrophila, and reduced and delayed mortality (up to five days) in A. siamensis infection. A developed indirect ELISA with a sensitivity of 2 ng/mL revealed higher concentrations of septin 6 in liver, spleen, and brain tissues of rohu following A. hydrophila challenge. This work provides the first functional characterization of septin 6 in rohu, demonstrating its critical role in regulating immune responses and highlighting its potential in fish health management in aquaculture.