Colonial Ascidian Stem Cell Biology

Colonial ascidians, sessile marine invertebrates within the tunicate subphylum, possess remarkable capacities for regeneration and asexual reproduction underpinned by circulating stem cells. Unlike solitary ascidians, these organisms form genetically identical zooids organised in colonies, linked by a common vascular network through which undifferentiated, blood-borne stem cells migrate to sites of bud formation or injury. Stem cell populations in species such as Botryllus schlosseri and Botrylloides diegensis express conserved regulators including Vasa, Piwi and integrin-alpha-6, signalling through pathways such as Notch, Wnt and sphingosine-1-phosphate to orchestrate proliferation, homing and differentiation. Cyclical patterns of colonial growth and regression, sometimes repeating through fission events, reveal ageing and rejuvenation programmes that challenge conventional views of senescence in chordates. The tractability of ascidian stem cell systems offers insights into fundamental mechanisms of organogenesis, ageing and whole-body regeneration, with potential applications in regenerative medicine, tissue engineering and the study of stem cell niches in a chordate context.

Research from Nature Portfolio

Recent studies have characterised recurring ageing and rejuvenation sequences in colonies of Botryllus schlosseri, termed the Orshina rhythm. By monitoring life-history strategies that incorporate or omit fission events, researchers uncovered periodic segments of colonial vigour, sexual maturation and either death or rejuvenation at roughly three-month intervals. This work highlights intrinsic scheduling of reproduction, stem cell activation and tissue regeneration within a chordate model. In parallel, studies in Botrylloides diegensis have demonstrated that a small subset of blood-borne cells expressing integrin-alpha-6, Pou3 and Vasa act as bona fide stem cells for whole-body regeneration. Ablation of these cells halts regenerative processes, whereas single-cell transplantation rescues colony restoration. Further analysis revealed that canonical Wnt and Notch signals regulate the proliferation and activation of these integrin-alpha-6+ stem cells. Together, these investigations define cellular identity and molecular cues critical for asexual regeneration and colonial homeostasis in ascidians.

Colonial Ascidian Stem Cell Biology publication trend

The graph below shows the total number of articles in colonial ascidian stem cell biology across all publications each year (not limited to Nature Index journals).

Technical terms

Blastogenesis: successive asexual budding cycle leading to the development of new zooids from existing tissues.

Whole-body regeneration (WBR): the capacity to reconstruct an entire organism from small tissue fragments.

Germ cell precursor: an undifferentiated cell that gives rise to gametes and is distinguished by specific molecular markers.

Asexual budding: a reproductive mode in which new individuals arise from the somatic tissues of the parent.

Stem cell niche: the specialised microenvironment that maintains stem cell properties and regulates their activity.

References

1. Improved Media Formulations for Primary Cell Cultures Derived from a Colonial Urochordate. Cells (2023).
2. The novel Orshina Rhythm in a colonial urochordate signifies the display of recurrent aging/rejuvenation sequels. Scientific Reports (2023).
3. Systemic Bud Induction and Retinoic Acid Signaling Underlie Whole Body Regeneration in the Urochordate Botrylloides leachi. PLOS Biology (2007).
4. Migration of germline progenitor cells is directed by sphingosine-1-phosphate signalling in a basal chordate. Nature Communications (2015).
5. Integrin-alpha-6+ Candidate stem cells are responsible for whole body regeneration in the invertebrate chordate Botrylloides diegensis. Nature Communications (2020).
6. Putative stem cells in the hemolymph and in the intestinal submucosa of the solitary ascidian Styela plicata. EvoDevo (2019).