BsTLR: a new member of the TLR family of recognition proteins from the colonial ascidian Botryllus schlosseri

Toll-like receptors (TLRs) represent a well-known family of conserved pattern recognition receptors the importance of which, in non-self recognition, was demonstrated in both vertebrates and invertebrates. Tunicates represent the vertebrate sister group and, as invertebrates, they rely only on innate immunity for their defense. As regards TLRs, two transcripts have been described and characterized in the solitary species Ciona robusta, referred to as CiTLR1 and CiTLR2. Using the Ciona TLR nucleotide sequences, we examined the available transcriptomes of Botryllus schlosseri looking for similar sequences. We were able to identify a sequence, with similarity to CiTLR2 and, through in silico transduction and subsequent sequence analysis, we studied the domain content of the putative protein. The sequence, called BsTLR, has a TIR and a transmembrane domain, four LLR and two LRR-CT domains. In addition, we analised bstlr transcription in vivo and in vitro, under various experimental conditions and in different phases of the Botryllus blastogenetic cycle. Our data show that, in different phases, there is a change in gene transcription and mRNA location, according to the blastogenetic phase.