Summary
During the first 10 minutes after the onset of metamorphosis in the ascidian Amaroucium constellatum there is a massive emigration of blood cells (granulocytes) from the hemocoel, across the epidermis, into the tunic. Electron microscopy has been employed to extend some of the classical observations of the last century. The new findings are compatible with the hypothesis that the blood cells follow a transcellular pathway. Our interpretation is as follows: an emigrating cell enters the basal part of an epidermal cell and becomes enclosed within a vacuole. The vacuole and the blood cell move to the apex of the epidermal cell. The vacuole fuses with the plasmalemma releasing the blood cell into the tunic. Blood cells can therefore pass through the epidermis without leaving a hole and without rupturing intercellular junctions.
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This investigation was supported in part by National Science Foundation Research Grant GB 5394. The authors thank Dr. John S. Edwards for stimulating discussions and for critically reading the manuscript.
A part of this investigation was carried out at the Friday Harbor Laboratories of the University of Washington. The cooperation of the Director, Dr. Robert L. Fernald in facilitating this work is greatly appreciated.
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Cloney, R.A., Grimm, L. Transcellular emigration of blood cells during ascidian metamorphosis. Z. Zellforsch. 107, 157–173 (1970). https://doi.org/10.1007/BF00335222
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DOI: https://doi.org/10.1007/BF00335222