Insight on signal transduction pathways involved in phagocytosis in the colonial ascidian Botryllus schlosseri

Tunicates are chordate invertebrates, closely related to vertebrates, which represent valuable organisms
for the study of a variety of biological processes from an evolutionary point of view. As invertebrates, they
rely on innate immunity to cope with foreign, potentially pathogenic material. Among tunicates, the compound
ascidian Botryllus schlosseri is emerging as a reliable model organism for the study of innate
immune responses. However, there is a general lack of knowledge on the signalling pathways activated
during immune responses and, in particular, in phagocytosis.
In the present work, we carried out a preliminary investigation of the signalling pathways involved in
phagocytosis, with particular reference to MAPK activation. We studied in vitro zymosan phagocytosis in
the presence of manumycin A, which inhibit the activation of Ras, PD98059, SP600125 and SB202190,
inhibitors of Erk, JNK and p38, respectively, parthenolide, N-acetyl-L-cysteine (NAC) and pyrrolidine
dithiocarbamate (PDTC), inhibiting NF-kB activation. In addition we carried out immunoblot and immunocytochemistry
analysis with the use of anti-pErk1/2, anti-pp38, anti-pJNK, anti-NF-kB (p50) and antipan
Ras antibodies. Results demonstrate that the recognition of foreign cells triggers a phosphorylation
cascade leading to the activation of Ras-like small GTPases, MAPKs and NF-kB and argue in favour of a
conservation, also in ascidians, of the main signalling pathways.