Identification of two MAPK transcripts in the colonial ascidian Botryllus schlosseri: involvement in immune and stress responses and potential roles in colony growth

Mitogen-activated protein kinase (MAPK) pathways are evolutionarily conserved signalling cascades that regulate fundamental cellular processes such as proliferation, differentiation, and stress responses. In the colonial ascidian Botryllus schlosseri, MAPK activity is required for efficient phagocytosis of non-self cells or particles. In the present study, we identified two novel MAPK transcripts in B. schlosseri and analysed their modulation during the colonial blastogenetic cycle under various experimental conditions. Since phagocytic activity is essential for the cyclical renewal of the colony throughout the blastogenetic cycle, we also investigated the effects of colony exposure to MAPK inhibitors, PD98059 and SP600125, targeting the ERK and JNK signalling pathways, respectively. Colonies were microinjected with the inhibitors, and changes in morphology and transcriptional profiles were analysed. The inhibition of MAPK activity altered colony development and modulated the expression of genes associated with oxidative stress protection (sod, gpx-5) and stress granule dynamics (tiar, ttp), processes involved in post-transcriptional regulation. These findings suggest that MAPK signalling is indispensable for the proper progression of the blastogenetic cycle in B. schlosseri, integrating oxidative stress defence and post-transcriptional control to maintain colony homeostasis.