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Serotonin (5-HT) is a key player in many physiological processes in both the adult organism and developing embryo. One of the mechanisms for 5-HT-mediated effects is covalent binding of 5-HT to the target proteins catalyzed by transglutaminases (serotonylation). Despite the implication in a variety of physiological processes, the involvement of serotonylation in embryonic development remains unclear. Here we tested the hypothesis that 5-HT serves as a substrate for transglutaminase-mediated transamidation of the nuclear proteins in the early embryos of both vertebrates and invertebrates. For this, we demonstrated that the level of serotonin immunoreactivity (5-HT-ir) in cell nuclei increases upon the elevation of 5-HT concentration in embryos of sea urchins, mollusks, and teleost fish. Consistently, pharmacological inhibition of transglutaminase activity resulted in the reduction of both brightness and nuclear localization of anti-5-HT staining. We identified specific and bright 5-HT-ir within nuclei attributed to a subset of different cell types: ectodermal and endodermal, macro-and micromeres, and blastoderm. Western blot and dot blot confirmed the presence of 5-HT-ir epitopes in the normal embryos of all the species examined. The experimental elevation of 5-HT level led to the enhancement of 5-HT-ir-related signal on blots in a species-specific manner. The obtained results demonstrate that 5-HT is involved in transglutaminase-dependent monoaminylation of nuclear proteins and suggest nuclear serotonylation as a possible regulatory mechanism during early embryonic development. The results reveal that this pathway is conserved in the development of both vertebrates and invertebrates.

Adrenal glands are the major organs releasing catecholamines and regulating our stress response. The mechanisms balancing generation of adrenergic chromaffin cells and protecting against neuroblastoma tumors are still enigmatic. Here we revealed that serotonin (5HT) controls the numbers of chromaffin cells by acting upon their immediate progenitor “bridge” cells via 5-hydroxytryptamine receptor 3A (HTR3A), and the aggressive HTR3Ahigh human neuroblastoma cell lines reduce proliferation in response to HTR3A-specific agonists. In embryos (in vivo), the physiological increase of 5HT caused a prolongation of the cell cycle in “bridge” progenitors leading to a smaller chromaffin population and changing the balance of hormones and behavioral patterns in adulthood. These behavioral effects and smaller adrenals were mirrored in the progeny of pregnant female mice subjected to experimental stress, suggesting a maternal-fetal link that controls developmental adaptations. Finally, these results corresponded to a size-distribution of adrenals found in wild rodents with different coping strategies.

The identification of tissue-specific promoters for gene therapeutic constructs is one of the aims of complex tumor therapy. The genes encoding the fibroblast activation protein (FAP) and the connective tissue growth factor (CTGF) can function in tumor-associated stromal cells but are practically inactive in normal adult cells. Accordingly, the promoters of these genes can be used to develop vectors targeted to the tumor microenvironment. However, the efficiency of these promoters within genetic constructs remains underexplored, particularly, at the organism level. Here, we used the model of Danio rerio embryos to study the efficiency of transient expression of marker genes under the control of promoters of the FAP, CTGF, and immediate early genes of Human cytomegalovirus (CMV). Within 96 h after the injection of vectors, the CTGF and CMV promoters provided similar equal efficiency of reporter protein accumulation. In the case of the FAP promoter, a high level of reporter protein accumulation was observed only in certain zebrafish individuals that were considered developmentally abnormal. Disturbed embryogenesis was the factor of changes in the exogenous FAP promoter function. The data obtained make a significant contribution to understanding the function of the human CTGF and FAP promoters within vectors to assess their potential in gene therapy.

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