The developmental potential of stem cells in Hydractinia symbiolongicarpus

Hydractinia is a sessile, colonial invertebrate and a member of the phylum Cnidaria. They possess a remarkable population of adult stem cells known as i-cells which are the source of Hydractinias impressive regenerative ability. Previous work had identified the presence of i-cells during embryogenesis and metamorphosis. I was able to show the first appearance of putative i-cell progenitors in early embryogenesis in Hydractinia. i-cell progenitors first appeared at the 32/64-cell stage, often with many individual cells at once expressing Piwi1 (which is an i-cell marker). The true developmental potential of these putative i-cell progenitors remains to be studied. Past studies have shown that a population of i-cells can give rise to all somatic cell lineages as well as germ cells in Hydractinia. However, whether this population consisted of distinct, lineage-committed i-cells or pluripotent cells has not yet been confirmed. This work determines the developmental potential of a single i-cell in Hydractinia. Making use of Hydractinia’s remarkable growth, plasticity, I established a method for transferring a single i-cell from a double transgenic Piwi1::GFP Beta-Tubulin::mScarlet reporter colony into a wild type animal via stolonal contact. This method allowed tracing all progeny of a single grafted icell in the host tissue in vivo. I observed that wild type Hydractinia tissue possessing an initial single transgenic donor i-cell developed into a chimeric animal with a mixture of cells derived from the transgenic donor and the wild type recipient. Donor-derived cells, representing all major somatic lineages and germ cells were scattered in the recipient’s tissues in both feeding and sexual polyps, and in the stolonal compartment. This study shows that Hydractinia possesses pluripotent i-cells. Additionally, somatic cell types in Hydractinia did not exhibit any stem cell like qualities such as continuous proliferation and passive displacement.

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University of Galway

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Attribution-NonCommercial-NoDerivatives 4.0 International

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University of Galway Theses (PhD Theses)