Serotonin in Early Sea Urchin Embryogenesis
Open AccessSerotonin-containing neurons are the first to develop in the mammalian embryo, and their cell processes eventually project into every region of the brain and spinal cord. Research on the function of serotonin has revolved around its role as a neurotransmitter in the central and peripheral nervous system. Although serotonin is mainly known for its role as a neurotransmitter, it is becoming increasingly apparent that it also has many diverse non-neuronal functions across species, and is present in plants, protozoans, and throughout the metazoans. Serotonin has also been implicated in the regulation of various morphogenetic events in preneural embryos including cardiac morphogenesis and establishment of left/right symmetry. In this Dissertation research I have utilized the sea urchin, Lytechinus pictus, to examine the role of serotonin in the gastrulation process. During gastrulation embryo cell rearrangements create the primary germ layers and are necessary for organ formation. Previous studies in our lab have shown that serotonin levels peak immediately prior to gastrulation in L. pictus embryos and that serotonin is synthesized by a non-neuronal tryptophan hydroxylase enzyme. Furthermore, serotonin receptor antagonists block gastrulation. These studies suggest that serotonin initiates the gastrulation process. My research examined the potential role of serotonin as the initiator of the gastrulation process in L. pictus sea urchin embryos. Previous studies in our lab suggest serotonin must act through a receptor-mediated signaling mechanism in these embryos. Seven major receptor types and approximately 30 subtypes have been identified in mammals that are collectively linked to many different signaling pathways. The types of serotonin receptors in the sea urchin genome have not been analyzed, and the receptor types involved in gastrulation are not known. Furthermore, while serotonin has been chemically detected in the blastula and gastrula embryos, its intraembryonic location is not known. In the studies described in the three Chapters of this Dissertation research I (1) determined the intraembryonic location of serotonin by confocal immunocytochemistry and examined the role of serotonin synthesis in the gastrulation process by studying the effects of serotonin synthesis inhibition; (2) performed a phylogenetic analysis of sea urchin serotonin receptors; and (3) determined which receptor(s) and signaling mechanism(s) are likely mediating gastrulation from pharmacological analyses and qPCR-generated developmental stage profiles of serotonin receptor transcripts.
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