Supplementary files and original datasets in the article “Genome-wide characterization of Toll-like receptor genes in Oreochromis niloticus and their involvement in brain immune response against Streptococcus agalactiae infection”

Streptococcus agalactiae (Group B Streptococcus) causes severe meningitis in tilapia (Oreochromis niloticus), leading to substantial economic losses in China. Toll-like receptors (TLRs), as pattern recognition receptors, play a pivotal role in innate immunity by helping the host defend against pathogenic threats. Despite their importance, a systematic characterization of TLR genes in tilapia has not been performed, and their response mechanisms in the brain remain poorly understood. In this study, we identified 19 TLR genes in the tilapia genome, including TLR1-1, TLR1-2, TLR2-1, TLR2-2, TLR2-3, TLR2-4, TLR3, TLR5M, TLR5S, TLR7, TLR8-1, TLR8-2, TLR8-3, TLR9, TLR13-1, TLR13-2, TLR13-3, TLR18, and TLR22. These genes contain conserved motifs typical of the TLR family and are distributed across 10 of the 22 chromosomes. Phylogenetic analysis classified these genes into five subfamilies: TLR1, TLR3, TLR5, TLR7, and TLR11, with the TLR4 subfamily absent. Integration of transcriptomic and single-cell data revealed that all 19 TLR genes are expressed across a variety of tissues and cells, with 14 of them (excluding TLR1-1, TLR2-3, TLR5S, TLR13-2, and TLR13-3) being expressed in the brain, particularly in the medulla oblongata. Furthermore, we examined the response of these 14 TLR genes to S. agalactiae infection in seven brain regions. Notably, TLR1-2, TLR2-1, TLR5M, TLR8-1, and TLR13-1 were significantly upregulated in response to S. agalactiae infection, indicating their crucial role in the tilapia brain’s innate immune defense against S. agalactiae. These findings enhance our understanding of the TLR gene family in tilapia and its role in the brain’s immune response to bacterial invasion.