Serotonergic-induced ion currents in cleaving sea urchin embryos

Electrophysiology and Fluorescence Spectroscopy Approaches for Evaluating Gamete and Embryo Functionality in Animals and Humans

This review has examined two of the techniques most used by our research group for evaluating gamete and embryo functionality in animal species, ranging from marine invertebrates to humans. Electrophysiology has given access to fundamental information on some mechanisms underpinning the biology of reproduction. This technique demonstrates the involvement of ion channels in multiple physiological mechanisms, the achievement of homeostasis conditions, and the triggering of profound metabolic modifications, often functioning as amplification signals of cellular communication. Fluorescence spectrometry using fluorescent probes to mark specific cell structures allows detailed information to be obtained on the functional characteristics of the cell populations examined. The simple and rapid execution of this methodology allowed us to establish a panel helpful in elucidating functional features in living cells in a simultaneous and multi-parameter way in order to acquire overall drafting of gamete and embryo functionality.

Non-Neuronal Transmitter Systems in Bacteria, Non-Nervous Eukaryotes, and Invertebrate Embryos

In 1921, Otto Loewi published his report that ushered in the era of chemical transmission of biological signals. January 2021 marked the 90th anniversary of the birth of Professor Gennady A. Buznikov, who was the first to study the functions of transmitters in embryogenesis. A year earlier it was 60 years since his first publication in this field. These data are a venerable occasion for a review of current knowledge on the mechanisms related to classical transmitters such as 5-hydroxytryptamine, acetylcholine, catecholamines, etc., in animals lacking neural elements and prenervous invertebrate embryos.

Ion currents in embryo development

Ion channels are proteins expressed in the plasma membrane of electrogenic cells. In the zygote and blastomeres of the developing embryo, electrical modifications result from ion currents that flow through these channels. This phenomenon implies that ion current activity exerts a specific developmental function, and plays a crucial role in signal transduction and the control of embryogenesis, from the early cleavage stages and during growth and development of the embryo. This review describes the involvement of ion currents in early embryo development, from marine invertebrates to human, focusing on the occurrence, modulation, and dynamic role of ion fluxes taking place on the zygote and blastomere plasma membrane, and at the intercellular communication between embryo cell stages.

5-HT-receptive structures are localized in the interblastomere cleft ofParacеntrotus lividusearly embryos

Local application of the agonists of serotonin receptors of third type 5-HTQ, SR57277A and quipazine into the interblastomere cleft of the sea urchinParacentrotus lividusembryo during first cleavage division, evokes specific membrane currents, whereas application of these drugs out of contact area show currents of lower amplitude and longer latent period. At the same time 5-HT3-receptor agonist quipazine imitates interblastomere signal in half embryos, but corresponding antagonists prevent it. Present data develop the hypothesis of protosynapse, demonstrating that the distribution of membrane serotonin receptors is limited to the period of cleavage division and localized in the interblastomere contact area. A possible role of spatial–temporal restriction of receptors at the interblastomere contact area is discussed in relation to the subsequent embryo development.

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.