Bioluminescence in the tunic of the colonial ascidian, Clavelina miniata: Identification of luminous cells in vitro

Abstract

In the colonial ascidian, Clavelina miniata, the tunic is a luminous tissue that contains three types of tunic cells: tunic phagocytes, tunic granulocytes, and morula-like tunic cells. Although tunic matrix is transparent, the high density of cells within the thick tunic makes it difficult to obtain images of luminescence induced by mechanical or osmotic stimulation. In order to discover which cell type emits light, tunic cells were isolated and subsequently transferred to glass slides in low density. The three types of tunic cells could be identified on the glass slides, and they remained alive for at least at few hours. When tunic cells were treated with hypotonic or hypertonic seawater, only the tunic phagocytes showed luminescence that was monitored with a photon-counting camera connected with a microscope. Similar results were obtained when cells were punctured with a microneedle. Tunic phagocytes luminesced immediately after their lysis, but morula-like tunic cells and tunic granulocytes did not show any luminescence. The maximum wavelength of the luminescence was 535 nm. Thus it is concluded that the tunic phagocytes are the source of light in C. miniata.