Development of the γ-amino butyric acid (GABA)-ergic signaling system and its role in larval swimming in sea urchin

Abstract

SUMMARYThe present study aimed to elucidate the development and γ-amino butyric acid (GABA)-ergic regulation of larval swimming in the sea urchin Hemicentrotus pulcherrimus by cloning glutamate decarboxylase (Hp-gad), GABA A receptor (Hp-gabrA) and GABA A receptor-associated protein (Hp-gabarap), and by performing immunohistochemistry. The regulation of larval swimming was increasingly dependent on the GABAergic system, which was active from the 2days post-fertilization (d.p.f.) pluteus stage onwards. GABA-immunoreactive cells were detected as a subpopulation of secondary mesenchyme cells during gastrulation and eventually constituted the ciliary band and a subpopulation of blastocoelar cells during the pluteus stage. Hp-gad transcription was detected by RT-PCR during the period when Hp-Gad-positive cells were seen as a subpopulation of blastocoelar cells and on the apical side of the ciliary band from the 2d.p.f. pluteus stage. Consistent with these observations, inhibition of GAD with 3-mercaptopropioninc acid inhibited GABA immunoreactivity and larval swimming dose dependently. Hp-gabrA amplimers were detected weakly in unfertilized eggs and 4d.p.f. plutei but strongly from fertilized eggs to 2d.p.f. plutei, and Hp-GabrA, together with GABA, was localized at the ciliary band in association with dopamine receptor D1 from the two-arm pluteus stage. Hpgabarap transcription and protein expression were detected from the swimming blastula stage. Inhibition of the GABA A receptor by bicuculline inhibited larval swimming dose dependently. Inhibition of larval swimming by either 3-mercaptopropionic acid or bicuculline was more severe in older larvae (17 and 34d.p.f. plutei) than in younger ones (1d.p.f. prism larvae).

Mechanisms of the epithelial-to-mesenchymal transition in sea urchin embryos

“…8 Thus, the NMC ingression should be associated with the local break down of the basal lamina as it is in PMCs and NSMCs. An ECM protease astacin gene, SpAN/SpANlike, has been detected mainly in the animal ectoderm from the early blastula stage to the early gastrula stage (Table 3-2) 94 by in situ hybridization in S. purpuratus 145 and has a similar distribution pattern to that of Hp-gad transcribing cells in H. pulcherrimus 128 . Although they show a very interesting similar spatial distribution, whether the Hp-gad and SpAN/SpAN-like genes are transcribed in the same cell is not known.…”

“…5 The Hp-GAD expressing cells (GADC) are involved in larval swimming activity. 128 Ingression of ECPN cells and GADC occurs soon after the expression of each gene, which is significantly earlier than ingression of PMCs. The third NMC gene, 5HThpr, is transcribed in a cell group that ingress during gastrulation ( Table 3-2).…”

“…The cells constitute the major blastocoelar cell network 13 that contributes in transmission of serotonin signal to the ciliary epithelium to regulate larval swimming activity. 128 …”

“…144 The EMT of NMCs Recent neurogenetic studies of H. pulcherrimus have detected mesenchymal cells that express genes and proteins including encephalopsin, 5 5HThpr, 4 GAD, 4,128 and GABA (a neurotransmitter) 128 during the swimming blastula stage, in which PMC ingression is not yet occurred. Among these cell types, 5HThpr cells cannot be eliminated completely by removing the entire archenteron by microsurgery at the early gastrula stage, 13 indicating that NSMCs alone are not the ancestors of these cells.…”

Neurophysiological control of swimming behaviour, attachment and metamorphosis in black-footed abalone (Haliotis iris) larvae

“…In addition, GABAergic (Katow et al 2013), peptidergic (Baloun & Morse 1984;Trapido-Rosenthal & Morse 1986). In the present study, such variations were reduced by using the same batch of larvae and testing simultaneously across the treatments and control.…”