Identification and annotation of the T cell receptor beta (TCRβ) locus in large yellow croaker (Larimichthys crocea)

The T cell receptor (TCR) plays a crucial role in antigen recognition and signal transduction during T cell immunity. While the TCR locus has been well characterized in mammals, its knowledge in teleosts remains limited. In this study, we identified the TCRβ locus in large yellow croaker (Larimichthys crocea), an important mariculture species in China, and found 31 V, 2 D, 13 J, and 2 C gene segments. The 2 C gene segments are highly similar in amino acid sequences, and share conserved residues with TCRβ from other species. A consensus recombination signal sequence (RSS) is found to flank the V, D, and J gene segments, with conserved spacer lengths as observed in mammals. The V gene segments are consisted of a leader exon, an intron, and a V_β exon, and could be categorized into fourteen families based on the nucleotide identity. Furthermore, we found that the recombination of V, D, and J gene segments in the TCRβ locus occurred at the genomic DNA level, followed by fusion with the C gene segments at the mRNA level. Additionally, the usage of J gene segments is restricted to their adjacent downstream C gene segments. qRT-PCR analysis showed that the TCRβ was highly expressed in immune organs and was upregulated after PHA treatment. By exploring a previously published RNA-seq dataset, we found that the V gene segments were differentially expressed after P. plecoglossicida infection, suggesting their involvement in T cell immunity. In summary, we characterized the TCRβ locus in large yellow croaker, which would promote the understanding of T cell immunity in teleosts.