Pre-neural serotonin influences late embryonic development and behavior patterns in zebrafish. Expression data from 2 and 4 dpf zebrafish larvae.

The presence of serotonergic system during early pre-neural development is conserved amongst all studied invertebrate and vertebrate animals. Previously, we discovered that early embryonic pre-neural serotonin relays physiological and behavioral information from mother to progeny in an invertebrate model system. However, the question of whether the similar logic might apply during vertebrate development remains unanswered. Thus, we took advantage of zebrafish model system to address this based on the systematic investigation of composition and function of early pre-neural serotonergic system in fish. As a result, we characterized the presence, distribution and activity of molecules involved in serotonin synthesis and transport at pre-neural and neural stages of development. Then, we experimentally revealed the existence of delayed developmental and behavioral effects resulting from the manipulations of pre-neural (zygote, blastula and gastrula) serotonergic system. In particular, the delayed effects included differences in the synthesis of serotonin in early serotonergic neurons in the central nervous system as well as in behavioral alterations in zebrafish larvae. At the same time, the effects resulting from manipulations of pre-neural serotonin appeared highly specific and did not coincide with any major abnormalities. Similar manipulations of the serotonergic system at later neural stages did not show similar effects, thus, demonstrating that transduction of a serotonergic signal is not based on the general level of retained serotonin but on its availability in the specific cells. Accordingly, gene expression analysis demonstrated specific changes in response to the elevation of early pre-neural serotonin, which included the delayed and pre-mature onsets of different gene expression programs. Taken together, our results introduce a novel function of early pre-neural serotonergic system in a vertebrate embryo – tuning and fine control of specific mechanisms at later neural developmental stages that result in a mild variation of an adaptive spectrum. We used microarrays to identify the aftermath of early pre-neural serotonin increase and decrease. Injections of embryos were performed at the using Eppendorf FemtoJet microinjector. We co-injected serotonin of reserpine with lysine-fixable TRITC-conjugated fluorescent dextran (Molecular Probes, USA). Total RNA was extracted from 30-40 2 and 4 dpf zebrafish larvae from each experimental group. Total RNA from each sample was used for the synthesis of cDNA, which was hybridized to 902007 Affymetrix® Zebrafish Gene 1.0 ST Array with Ambion WT terminal labeling and hybridization protocol. Experiments and controls were done in biological duplicates.