Characterization and expression profiling of fadd gene in response to exogenous Aeromonas hydrophila or Edwardsiella tarda challenge in the hybrid yellow catfish (Pelteobagrus fulvidraco ♀ × P. vachelli ♂).

In mammals, fas-associated protein with death domain (FADD) is involved in the process of cell apoptosis and plays a key role in innate immune signaling. Nevertheless, its detailed molecular mechanisms underlying apoptosis and immune responses to exogenous bacterial infections in teleosts remain largely unknown. In this study, a group of 60 hybrid yellow catfish (with the body weight of 25 ± 0.5 g) were used in subsequent experiments, we examined the expression profiling of fadd gene through comparative genomics and comparative immunological methods. Our results showed that fadd in the hybrid yellow catfish (hycfadd) exhibited similar gene and spatial structures to those in other vertebrates, and formed an independent clade in phylogeny. An expression pattern analysis revealed that hycfadd widely transcribed in various tissues, with the highest transcription level in the liver. Furthermore, expression profiling of hycfadd when intraperitoneally infected with 50 μL of exogenous Aeromonas hydrophila (2.0 × 107 CFU/mL) or Edwardsiella tarda (2.0 × 107 CFU/mL) within 48 h were significantly up-regulated in the kidney, spleen, liver and intestine. Important genes in the toll like receptor (tlr) 1-tlr2- myeloid differentiation primary response 88 (MyD88)-fadd-caspase (casp) 8 cascades of TLR signaling pathway in liver were significantly up-regulated after the A. hydrophila stimulation, suggesting that apoptosis through the TLR signaling pathway may have been triggered and activated, which were further verified in the liver, kidney, spleen, intestine and gill by a TUNEL assay. Overall, this study provides solid evidence for the bacterial induction of fadd-related apoptosis in teleosts.