Central nervous system regeneration in ascidians: cell migration and differentiation

Area of Science:

• Marine biology
• Neuroscience
• Stem cell research

Background:

• Adult ascidians possess remarkable central nervous system (CNS) regeneration capabilities, making them valuable models for neuroregeneration studies.
• The potential involvement of undifferentiated blood cells (hemocytes) in adult neuroregeneration requires detailed investigation.

Purpose of the Study:

• To analyze the migration, circulation, and functional role of hemocytes in the neuroregeneration process of the ascidian Styela plicata.
• To investigate whether hemocytes contribute to the repair of the CNS after induced neurodegeneration.

Main Methods:

• Hemocytes were labeled with superparamagnetic iron oxide nanoparticles (SPION) and reintroduced via autologous transplant.
• Neurodegeneration was induced using 3-acetylpyridine (3AP).
• Magnetic resonance imaging (MRI), immunohistochemistry, and transmission electron microscopy (TEM) were used to track hemocytes and assess cellular changes.

Main Results:

• SPION-labeled hemocytes successfully migrated to the CNS, intestinal region, and siphons within 1-10 days post-injury.
• Migrated hemocytes in the CNS were identified as putative stem cells (PIWI-positive cells).
• Hemocytes in the neural ganglion began expressing β-III tubulin, a neural marker, 10 days after injury, indicating differentiation. Undifferentiated hemocytes were observed in the neural gland, a potential neurogenic niche.

Conclusions:

• Hemocyte migration to injured CNS sites is crucial for ascidian neuroregeneration.
• Ascidian hemocytes, particularly PIWI-positive cells, possess stem cell-like properties and can differentiate into neural cells.
• The neural gland may serve as a previously unrecognized neurogenic niche in ascidians, supporting hemocyte-mediated regeneration.