Expression of tryptophan 5‐hydroxylase gene during sea urchin neurogenesis and role of serotonergic nervous system in larval behavior

Abstract

Tryptophan 5-hydroxylase (TPH) is the rate-limiting enzyme in the biosynthesis of serotonin. cDNA cloning of TPH was carried out, and the occurrence of spatiotemporal transcription of TPH message was examined in larvae of the sea urchin, Hemicentrotus pulcherrimus (HpTPH), with in situ hybridization by using the tyramide signal amplification (TSA) technique and Northern hybridization. Based on deduced amino acids sequence of HpTPH, phylogenetically sea urchin locates at the closest position to vertebrates among invertebrates, and HpTPH had common conserved sequences in a catalytic domain. Initiation of HpTPH transcription occurred at the late gastrula stage exclusively in serotonin cells of apical ganglion (SAG) that was composed of a cluster of HpTPH-positive cells and the negative cells in between. In situ hybridization showed that the mRNA expression pattern was similar to the immunohistochemical localization of serotonin cells reported before (Bisgrove and Burke [1986] Dev. Growth Differ. 28:557-569; Yaguchi et al. [2000] Dev. Growth Differ. 42:479-488). p-Chlorophenylalanine (CPA), an irreversible inhibitor of TPH activity, considerably decreased serotonin content in the serotonin cells, whereas the HpTPH expression pattern and timing, and the extension of neurofibers from SAG cells were apparently unaffected, suggesting CPA exclusively perturbed synthesis of serotonin but not nervous system organization. CPA-treated larvae did not swim, despite the occurrence of ciliary beating in culture chamber, suggesting that proper serotonin synthesis is necessary for normal swimming of the larvae.

Spatio-temporal expression of a Netrin homolog in the sea urchin Hemicentrotus pulcherrimus (HpNetrin) during serotonergic axon extension

“…Although the onset of transcription was well before the apical ganglion formation at 24-hpf prism stage (e.g. Yaguchi et al, 2000;Yaguchi and Katow, 2003), it distinctively decreased in 48-hpf plutei when formation of the serotonergic nervous system was still in progress.…”

“…Biol. 52: 1077-1088 (2008) Yaguchi and Katow, 2003), and the serotonin receptor cell network in the blastocoel (Katow et al, 2004;Katow et al, 2007). Like most neural wiring mechanisms, the neural plexus formation at the apical ganglion of the echinolarvae is associated with intricate weaving of the axons on the basal surface of the oral lobe ectoderm (Yaguchi et al, 2000).…”

Gonad-stimulating substance-like molecule from the radial nerve of the sea cucumber

“…The exploration of nervous system in the echinoderm larvae and adult made great strides during past decade in sea urchins (e. g. Beer et al, 2001;Sly et al, 2002;Yaguchi and Katow, 2003;Katow et al, 2004;Nakajima et al, 2004;Burke et al, 2006;Katow et al, 2007;Katow, 2008), starfishes (e.g. Elphick et al, 1995;Byrne et al, 2005), sea cucumbers (e.g.…”

“…The function of the echinoderm nervous systems, however, remains obscure, except a few reports, such as relaxation of cardiac stomach preparation by SALMFamide (Elphic et al, 1995), inhibiting gonad-stimulating substance secretion by SALMFamide in starfish (Mita et al, 2004), and controlling larval swimming by the serotonergic nervous system in sea urchin larvae (Yaguchi and Katow, 2003;Katow et al, 2007).…”

In situ hybridization on whole larvae: a novel method for monitoring bivalve larvae

“…Ueki et al 1994), sea urchins (e.g. Yaguchi & Katow 2003), gastropods (Nederbragt et al 2002), and the oyster Crassostrea gigas (Fabioux et al 2004).…”