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Updated: May 17, 2026
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Published on: May 13, 2019
Identification and expression analysis of two Toll-like receptor genes from sea cucumber (Apostichopus japonicus)
Hongjuan Sun1, Zunchun Zhou, Ying Dong
1Liaoning Key Laboratory of Marine Fishery Molecular Biology, Liaoning Ocean and Fisheries Science Research Institute, Dalian, Liaoning 116023, PR China.
Abstract:
Toll-like receptors (TLRs) are a family of type I integral membrane glycoproteins which play pivotal roles in innate immunity. In this study, two TLRs named AjTLR3 and AjToll were cloned from sea cucumber (Apostichopus japonicus). The full-length cDNA sequences of AjTLR3 and AjToll are 3484 bp and 4211 bp, with an open reading frame (ORF) of 2679 bp and 2853 bp, encoding 892 and 950 amino acids, respectively. Both AjTLR3 and AjToll are composed of a leucine-rich repeat (LRR) domain, a transmembrane (TM) domain and an intracellular Toll/interleukin-1 receptor (TIR) domain. Evolution analysis revealed that AjTLR3 and AjToll were clustered with the vertebrate-like TLRs (V-TLRs) and the protostome-like TLRs (P-TLRs), respectively. These two genes were widely expressed in all five tested tissues (body wall, coelomocytes, tube feet, intestine and respiratory tree), but showed different expression patterns. The significantly up-regulated expressions of AjTLR3 and AjToll after peptidoglycan (PGN), lipopolysaccharides (LPS), Zymosan A and polyinosinic-polycytidylic acid (PolyI:C) challenges suggested that they were functionally involved in the immune responses to the Cram-positive bacteria, Gram-negative bacteria, fungi and double-stranded RNA (dsRNA) viruses, respectively.
Insights
Researchers identified two Toll-like receptors (TLRs) in sea cucumbers, AjTLR3 and AjToll. These receptors are crucial for innate immunity, showing varied expression and responding to different immune challenges like bacteria and viruses.
Area of Science:
- Marine biology
- Immunology
- Molecular biology
Background:
- Toll-like receptors (TLRs) are key regulators of innate immunity in many organisms.
- Sea cucumbers possess a unique immune system that warrants further investigation.
Purpose of the Study:
- To clone and characterize two novel TLRs, AjTLR3 and AjToll, from the sea cucumber Apostichopus japonicus.
- To investigate the expression patterns and immune response functions of these TLRs.
Main Methods:
- Full-length cDNA sequencing of AjTLR3 and AjToll.
- Bioinformatic analysis of TLR domains and evolutionary relationships.
- Gene expression analysis in various tissues and after immune stimulation.
Main Results:
- AjTLR3 and AjToll cDNA sequences were determined, encoding proteins with conserved TLR domains (LRR, TM, TIR).
- Evolutionary analysis placed AjTLR3 with vertebrate-like TLRs and AjToll with protostome-like TLRs.
- Both genes were expressed in all tested tissues, with distinct patterns, and significantly upregulated upon challenge with PGN, LPS, Zymosan A, and PolyI:C.
Conclusions:
- AjTLR3 and AjToll are novel sea cucumber TLRs involved in innate immunity.
- These TLRs play distinct roles in recognizing and responding to a range of immune stimuli, including Gram-positive bacteria, Gram-negative bacteria, fungi, and dsRNA viruses.
