DEVELOPMENTAL PLASTICITY, THE JAK/STAT PATHWAY AND DYNAMICS OF STEM CELL NICHES IN THE COLONIAL TUNICATE BOTRYLLUS SCHLOSSERI

The colonial ascidian Botryllus schlosseri, a close relative of vertebrates, is an exceptional model for exploring development, immunity, regeneration, and evolutionary biology. Its asexual life cycle involves the synchronous replacement of adult zooids by new buds, offering a unique opportunity to study intergenerational renewal and colony-level plasticity. This thesis investigates two integrated aspects of B. schlosseri biology. First, I present a comprehensive analysis of zooid plasticity across multiple blastogenetic cycles, combining morphological (zooid size) and physiological (heartbeat frequency) parameters. The findings reveal that traits are not fixed but vary with developmental stage and generational context, highlighting dynamic interplays between individuality and colony homeostasis. Second, I provide the first structural and functional characterization of the JAK/STAT signalling pathway in tunicates, showing its evolutionary conservation and dual role in immunity and stem cell regulation. Together, these studies reinforce B. schlosseri as a powerful model to investigate conserved processes linking regeneration, plasticity, and immune regulation.