Dicyemid's dilemma: structure versus genes. The unorthodox structure of dicyemid reproduction.

The clear phylogenetic status of the enigmatic Phylum Dicyemida is still uncertain. Their primitive body plan lacks essential metazoan synapomorphies, while genetic data favor a kinship with higher lophotrochozoans. This ultrastructural study increases the confusion about this phylum by presenting an unusual gonad and sperm structure lacking all synapomorphies essential for the various phyla of the lophotrochozoans, either free-living ones or parasites. In Dicyema typus, gonadogenesis is reduced to a single somatic cell, i.e., the infusorigen's axial cell that functions as a somatic gonadal founder cell as soon as a spermatogonium takes residence in its cytoplasm. The spermiogenic cells resulting therefrom are not connected by intercellular bridges and permanently contain a bundle of microtubules in their cytoplasm, obviously a kind of "dormant" spindle having assembled without centrosomes. Primary spermatocytes develop so-called polycomplexes, multiple synaptinemal complexes. The structure of the sperm is based on a certain kind of somatic cell that has been minimally adapted to function as a sperm. The mature sperm consists in only three organelles: an ovoid nucleus with a somatic chromatin structure, numerous pore complexes and a centrally arranged cluster of coiled tubular structures; a bundle of microtubules embedded into a rim running along the nucleus longitudinal surface, projecting out of the cell like a spear; and a lipid vesicle tightly attached to one pole of the nucleus, touching there the adjacent bundle of microtubules. Immunelectron microscopy confirms the somatic condition of mature sperm, revealing somatic histone H1 immunoreactivity over the nucleus, which can be interpreted as synapomorphy shared with Protozoa, Porifera and Cnidaria. Fertilization occurs as selfing, where the sperm penetrates, "bundle of microtubules first", a primary oocyte attached vis-à-vis on the other side of the plasma membrane of the infusorigen's axial cell. This somatic situation points to an ancient evolutionary model rather than to a condition caused by retrogression due to their life as commensals.

Effects of taxol treatment on the microtubular system and mitochondria of Tetrahymena.

Complex investigation was done using immunocytochemical confocal microscopy, electron microscopy and flow cytometry on the effect of taxol to the microtubular arrangement and dynamics. The most interesting phenomenon was the rapid disappearance of transversal microtubule bands, while longitudinal microtubule bands remained and were submitted to the known effects of taxol. There was a broad variation in mitochondrial effect, some of them remained normal, while others swollen, desintegrated and their tubules disoriented. Treatment with 50 nM taxol significantly reduced the binding of anti alpha-tubulin antibody and a lesser degree anti-acetylated tubulin antibody. The difference between the transversal and longitudinal microtubules is emphasized by the results and the paper discusses the possibilities of indirect effects of taxol to the transversal microtubules (tubulin-GTP interaction, faster turnover, mitochondrial interaction). Polyglutamylation of tubulin has not a role in this difference.

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.