Identification of novel antimicrobial peptides and histone-derived cryptides in the hepatic transcriptome of Nile tilapia (Oreochromis niloticus) infected with Streptococcus agalactiae.
This study identifies new antimicrobial peptides in Nile tilapia that respond to bacterial infection, expanding the understanding of fish immunity.
Where it sits
this study against the rest of the thymosin alpha-1 corpusSummary and findings
This study identified antimicrobial peptides and histone-derived cryptides in Nile tilapia infected with Streptococcus agalactiae. High-throughput RNA sequencing and quantitative real-time PCR were used to evaluate the expression of 13 high-confidence candidates. The study highlights the structural divergence of piscidin variants and the transcriptional response of AMPs over a 48-hour post-infection period.
Abstract
Nile tilapia (Oreochromis niloticus) is a valuable freshwater fish species widely cultured globally and in China. Its aquaculture production is challenged by Streptococcus agalactiae, the primary etiological agent of streptococcosis. Antimicrobial peptides (AMPs) play a critical role in the innate immune system of fish, exhibiting defensive and inhibitory effects against a wide range of pathogens. This study aimed to identify antimicrobial peptides and histone-derived cryptides in the Nile tilapia. We combined high-throughput RNA sequencing (RNA-seq) of S. agalactiae-infected tilapia hepatic tissue with in silico alignment against specialized AMP databases (APD and DRAMP). Putative candidates were evaluated via AlphaFold 3 structural modeling and validated in vivo through quantitative real-time PCR (qPCR) over a 48-hour post-infection period. Our transcriptomic profiling identified 13 high-confidence candidates: 7 classical candidates including two conserved transcripts (NK-lysin, hepcidin), two structural variants (piscidin 2, piscidin 3), and three (LEAP-2, thymosin β4, and lysozyme C) to be experimentally validated for the first time, alongside 6 novel histone-derived cryptides (Acipensin 1, Acipensin 2, Acipensin 6, Hipposin, SpHistin, and VK10) in Nile tilapia liver. In addition, AMPs and cryptides were subjected to sequence characterization and protein structure analysis. The expression change patterns of 7 AMP candidates alongside the canonical H2A (representative of histone proteins) were examined using qPCR. Significantly, our findings highlight the structural divergence of piscidin variants and the prediction of non-classical cryptides, which coincide with the transcriptional shutdown of canonical histone H2A. While classical AMPs exhibited a coordinated time-dependent expression pattern, progressing from an early enzymatic response to late nutritional immunity, this study fundamentally expands the known teleost immunological repertoire with these newly identified AMP molecules, emphasizing the defensive role against S. agalactiae infection.
Background
This paper addresses the role of antimicrobial peptides (AMPs) in the innate immune system of Nile tilapia, particularly in response to Streptococcus agalactiae, a significant pathogen in aquaculture. Prior research has established the importance of AMPs in fish immunity, but the specific peptides involved in this context were not fully characterized. The study aims to expand the understanding of the teleost immune repertoire by identifying novel AMPs and cryptides.
Methods
The study utilized high-throughput RNA sequencing (RNA-seq) on hepatic tissue from S. agalactiae-infected Nile tilapia. The population consisted of Nile tilapia, with putative AMP candidates evaluated through in silico alignment and validated via quantitative real-time PCR (qPCR) over a 48-hour post-infection period. The primary outcome measures included the identification and expression patterns of AMPs and cryptides.
Results
The study identified 13 high-confidence candidates, including 7 classical AMPs and 6 novel histone-derived cryptides. The expression patterns of the classical AMPs were characterized as coordinated and time-dependent, progressing from an early enzymatic response to late nutritional immunity. Specific details on numeric findings, such as expression levels or statistical significance, were not provided in the abstract.
Interpretation
The findings contribute to the existing literature by identifying new AMP candidates and expanding the understanding of immune responses in teleosts. While the study demonstrates significant findings regarding the expression of AMPs, the clinical relevance to human health remains unclear. Limitations include the focus on a single species and the lack of direct human applicability.
Key findings
- Identified 13 high-confidence candidates: 7 classical and 6 novel histone-derived cryptides.
- Classical AMPs exhibited a coordinated time-dependent expression pattern.
- Two conserved transcripts (NK-lysin, hepcidin) were among the classical candidates.
- Experimental validation of three candidates (LEAP-2, thymosin β4, lysozyme C) was conducted for the first time.
- The study expands the known immunological repertoire of teleosts.
Limitations
- Not applicable to human health.
- Focused on a single species, Nile tilapia.
- No direct clinical implications reported.
- Short follow-up period of 48 hours.