Serotonin immunoreactivity in a highly enigmatic metazoan phylum, the pre-nervous Dicyemida.
Dicyemida are simply organized metazoans with a long axial cell surrounded by a layer of ciliated peripheral cells. Stem cells and propagates develop inside the cytoplasm of the axial cell. Two types of propagates exist, asexually formed vermiform embryos and sexually derived infusoriform larvae, neither of which, however, develop by gastrulation. Thus, Dicyemida lack all traits typical of common metazoa and represent a pre-nervous state of organization. In this study, immunofluorescence and immunoelectron microscopy have been used to investigate the presence of a serotonin-like molecule in adults and larvae of Dicyema typus and Dicyemennea antarcticensis. Generally, in the adults of both species, the main immunoreactive structures are confined either to small vesicles inside the peripheral cells or to prominent vesicles in the axial cell, the latter vesicles apparently playing a role during the differentiation of the stem cells and the development of the propagates. In all stages, faint immunoreactivity can be observed over the surface membrane and the ciliary apparatus and over the heterochromatic blocks in the nuclei. Surprisingly, in the infusoriform larva, striking immunoreactivity occurs in the vesicles of the capsule cells covering the urn cells, which contain germinal cells. These vesicles might represent stores used in a later life phase of the animal. The results suggest that, in the pre-nervous Dicyemida, serotonin in its ancestral form may function as a hormone regulating essential developmental and morphogenetic processes.
Czaker
Renate
R
Center of Anatomy and Cell Biology, Laboratory of Comparative Cell Biology, Medical University of Vienna, Schwarzspanierstrasse 17, A-1090 Vienna, Austria. renate.czaker@meduniwien.ac.at
D000818:Animals; D007150:Immunohistochemistry; D007448:Invertebrates / Q000033:anatomy & histology* / Q000145:classification / Q000166:cytology* / Q000648:ultrastructure; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D012701:Serotonin / Q000276:immunology*
D012701:Serotonin