Characterization of Ambra1 in asexual cycle of a non-vertebrate chordate, the colonial tunicate Botryllus schlosseri, and phylogenetic analysis of the protein group in Bilateria.

Ambra1 is a positive regulator of autophagy, a lysosome-mediated degradative process involved both in physiological and pathological conditions. Nowadays, Ambra1 has been characterized only in mammals and zebrafish. Through bioinformatics searches and targeted cloning, we report the identification of the complete Ambra1 transcript in a non-vertebrate chordate, the tunicate Botryllus schlosseri. Tunicata is the sister group of Vertebrata and the only chordate group possessing species that reproduce also by blastogenesis (asexual reproduction). B. schlosseri Ambra1 deduced amino acid sequence is shorter than vertebrate homologues but still contains the typical WD40 domain. qPCR analyses revealed that the level of B. schlosseri Ambra1 transcription is temporally regulated along the colonial blastogenetic cycle. By means of similarity searches we identified Wdr5 and Katnb1 as proteins evolutionarily associated to Ambra1. Phylogenetic analyses on Bilateria indicate that: (i) Wdr5 is the most related to Ambra1, so that they may derive from an ancestral gene, (ii) Ambra1 forms a group of ancient genes evolved before the radiation of the taxon, (iii) these orthologous Ambra1 share the two conserved WD40/YVTN repeat-like-containing domains, and (iv) they are characterized by ancient duplications of WD40 repeats within the N-terminal domain.