Molecular Characteristics and Evolutionary Relationships of Toll-Like Receptor (TLR21) of Indonesian KUB-1 Chicken

Abstract

In vertebrates, the immune system has several Toll-like receptors (TLRs) to recognize specific pathogen-associated molecular patterns (PAMPs).  In aves, TLR21 is known to be a functional homolog of TLR9 in mammals.  This study aimed to determine the molecular characteristics of TLR21 in KUB-1 chicken, a superior breed of Indonesian local chicken, and their evolutionary relationship.  The TLR21 gene was obtained from the ovarian RNA extraction and synthesized into cDNA by reverse transcription.  We found that the cDNA sequence of the TLR21 of KUB-1 chicken has a length of 3504 bp, including a 2823 bp open reading frame (ORF), which encodes a putative protein of 940 amino acids (aa).  The deduced KUB-1 chicken TLR21 protein consisted of 720 aa in the extracellular domain containing 20 LRRs, 23 aa in the transmembrane region, and 141 aa of Toll‐IL‐1 receptor in the intracellular domain, and had a molecular weight of 107 kDa.  The KUB-1 chicken TLR21 had homology of about 99%, 76%, and 43% with other TLR21 from other breeds of chicken, non-chicken poultry, and fish, respectively.  Its molecular character was conserved throughout the evolution of TLR21 in chicken, so the KUB-1 chicken was not much different from the broiler.  However, there has been an evolution in duck and goose, although the function is still the same.  Evolutionarily, Gallus gallus_KUB-1 TLR21, which belongs to the TLR11 Family, has differentiated from fish TLR21 and formed a paraphyletic relationship with TLR21 in Anser cygnoides and Anas platyrhynchos.