Epithelial cell layers that define the boundaries between tissue and the external environment, and that divide the body into discrete sections, are a critical feature or all multicellular animals. Mechanisms to repair damage to epithelial layers are similarly ancient. Our earlier work characterized the process of wound healing in Clytia and demonstrated that many healing mechanisms are conserved between Clytia and more complex animals, including vertebrates. This finding suggests that these mechanisms emerged at least 600 million years ago, before the divergence of cnidarians from the bilaterian lineage. We are currently using Clytia to study the evolutionary origins of wound healing and to gain insights into those mechanisms that are shared across the tree of life.
Current Research Projects in the Lab
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1. How does the extracellular matrix (ECM) interact with epithelial cells during wound healing?
We showed in previous work that the presence or absence of a basement membrane causes wound healing to switch from lamellipodia-based healing to purse-string healing (Kamran et al., 2017). The switch can be seen in the video below, where a tear in the basement membrane is apparent on the left side of the wound.
Note that lamellipodia do not extend across the basement membrane tear in the upper left part of the wound. Instead, this part of the wound closes with a purse string.
Clearly, attachment to the ECM and signaling between the ECM and the epithelial cells plays a major role in wound healing. We can interrogate these pathways by introducing growth factors or inhibitors directly into the ECM by microinjection. We are using this approach to perturb structural elements and signaling pathways that occur in the matrix and visualize the effects on wound healing.
2. What are the transcriptional changes associated with epithelial wound healing in Clytia?
Using approaches such as RNAseq, in situ hybridization, and single-cell sequencing, we are identifying genes whose expression is induced in the epithelium following wound healing and using mutagenesis to query the function of these genes. Below is our first successful mutagenesis experiment, in which we used CRISPR to knock out the endogenous GFP gene.
3. How do wounds heal in the lower epithelium of Clytia?
The lower epithelium of Clytia is very different from the upper epithelium. While the upper epithelial cells are flat and hexagonal, the lower epithelial cells have a complex shape as well as contractile fibers. This gives us the opportunity to contrast epithelial wound healing in two different types of epithelial cells that share an ECM in the same organism.
B) XZ orthogonal view. Outlined in blue and red rectangles are the separate “head” and “feet” layers of the epitheliomuscular cells. The depth of the z-stack is 11 µm.
B) Potential organization of lower epithelial muscular cells where the muscle feet touch the ECM (yellow) but the hexagonal heads do not. Drawing from Jahnel et al. 2014.
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