Abstract
Abstract Serotonin (5-HT) is not only a neurotransmitter but also a mediator of developmental processes in vertebrates. In this study, we analyzed the importance of 5-HT during zebrafish development. The expression patterns of three zebrafish tryptophan hydroxylase isoforms (Tph1A, Tph1B, Tph2), the rate-limiting enzymes in 5-HT synthesis, were analyzed and compared to the appearance and distribution of 5-HT. 5-HT was found in the raphe nuclei correlating with tph2 expression and in the pineal gland correlating with tph1a and tph2 expressions. Tph2-deficient fish generated with antisense morpholino oligonucleotides exhibited morphogenesis defects during pharyngeal arch development. The correct specification of neural crest (NC) cells was not affected in tph2 morphants as shown by the expression of early markers, but the survival and differentiation of pharyngeal arch progenitor cells were impaired. An organizing role of 5-HT in pharyngeal arch morphogenesis was suggested by a highly regular pattern of 5-HT positive cells in this tissue. Moreover, the 5-HT2B receptor was expressed in the pharyngeal arches and its pharmacological inhibition also induced defects in pharyngeal arch morphogenesis. These results support an important role of Tph2-derived serotonin as a morphogenetic factor in the development of NC-derived tissues.
Highlights
The pharyngeal arch cartilage in vertebrates is formed by neural crest (NC) cells
The expression patterns of three zebrafish tryptophan hydroxylase isoforms (Tph1A, Tph1B, Tph2), the rate-limiting enzymes in 5-HT synthesis, were analyzed and compared to the appearance and distribution of 5-HT. 5-HT was found in the raphe nuclei correlating with tph2 expression and in the pineal gland correlating with tph1a and tph2 expressions
These observations raised the intriguing possibility that the availability of 5-HT to NC cells may be a common denominator of craniofacial defects in both fgf8- and shh-deficient animals. 5-HT is a neurotransmitter but mounting evidence suggests that it plays a role in early development and morphogenesis of both invertebrates and vertebrates
Summary
The pharyngeal arch cartilage in vertebrates is formed by neural crest (NC) cells. These cells arise from the border between the neural ectoderm forming the neural tube and the non-neural ectoderm forming the epidermis [1]. We investigated the role of Tph1a, Tph2, 5-HT, and the 5-HT2B receptor during the development of the pharyngeal arches in the zebrafish. 5-HT was detected by HPLC in whole zebrafish embryos at different early stages of development starting from 8-cell, blastula, gastrula, 1 dpf, and 2 dpf stages (Figure 1A).
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