Impairment of symbiont photosynthesis increases host cell proliferation in the epidermis of the sea anemone Aiptasia pallida
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Corals exposed to environmental stresses need to engage appropriate physiological strategies to survive. Here, we examined tissue modifications following algal dysfunction. Aiptasia pallida was exposed during 1 week to 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), the herbicide called diuron. DCMU treatment produced a drastic loss in photosynthetic efficiency and a subsequent diminution of algae density over the following days. Cell proliferation evaluated by measuring the number of cells labeled with a thymidine analogue (EdU) revealed a significant increase in EdU+ cells in the epidermis after 1 week of DCMU incubation and in the gastrodermis at 4 weeks. TUNEL histology showed that the extent of cell death was, however, similar in the epidermis of control and treated specimens. In addition, we noticed a significant effect of DCMU treatment on the density of epidermal mucocytes after 1, 2 and 4 weeks. These results show that inhibition of Symbiodinium photosynthesis in the absence of any known direct effect of DCMU on host cells can induce an increase in epidermal host cell proliferation in both the epidermis and the gastrodermis. While new host gastrodermal cells are likely to promote tissue regeneration in order to recruit new algae, the new host epidermal cells may contribute to tissue adaptation following a decrease in energy income. Some of these new epidermal cells, such as mucocytes, may contribute to an eventual increase in the host heterotrophic ability until restoration of algal autotrophic contribution.
KeywordsSymbiodinium Cell Energy Income Gastrodermal Cell Symbiodinium Density Maximum Fluorescence Level
List of symbols
Contribution of heterotrophically acquired carbon to daily animal respiration
Initial fluorescence level
Maximum fluorescence level
Effective photochemical quantum yield
We thank the two anonymous reviewers for their helpful comments and the laboratory of Oceanology (ULg) for the diving PAM. DF is a recipient of a F.R.I.A PhD Studentship. JCP was supported by funding from the F.R.S.-F.N.R.S. (FRFC 2.4.631.09) and from the University of Liège (C-13/22). PAM was funded by ULg C-10/78 Fonds Spéciaux—crédits classiques. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Conflict of interest
The authors have declared that no conflict of interest.
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