Nakashima K, Kimura S, Ogawa Y, Watanabe S, Soma S, Kaneko T, Yamada L, Sawada H, Tung CH, Lu TM, Yu JK, Villar-Briones A, Kikuchi S, Satoh N.

Nat Commun. 2018 Aug 24;9(1):3402. doi:10.1038/s41467-018-05884-0

Chitin-based barrier immunity and its loss predated mucus-colonization by indigenous gut microbiota.

The gut cells of Ciona robusta are protected by a membrane made of cellulose and chitin, that bacteria can not cross. The three most abundant proteins in this membrane are Ci-MACPF1, related to perforins, variable region-containing chitin-binding protein (VCBP), and Ci-GFM1, a gel-forming mucin. Thus, the tunicate gut has features related to insects (chitin barrier) and vertebrates (mucin barrier).