Spatiotemporal expression pattern of an encephalopsin orthologue of the sea urchin Hemicentrotus pulcherrimus during early development, and its potential role in larval vertical migration

Abstract

We have cloned and studied Hp-ECPN, an encephalopsin orthologue of the sea urchin Hemicentrotus pulcherrimus. Hp-ecpn cDNA was produced and found to contain a 1461-bp open reading frame that encodes 486 amino acids. Accumulation of Hp-ecpn mRNA and protein expression occurred at the 14 h postfertilization (hpf) swimming blastula stage and thereafter. The Hp-ECPN protein was N-glycosylated, and the amino acid sequence was similar to that of vertebrate encephalopsins. Whole-mount immunohistochemistry revealed the presence of Hp-ECPN in cells (ECPN cells) that appeared initially around the tip of the archenteron in 20 hpf early gastrulae. By the 54 hpf pluteus stage, ECPN cells had spread through the aboral ectoderm, and, by the eight-arm pluteus stage, were restricted to the tips of the larval arms and the posterior end of the body. The number of ECPN cells increased under conditions of continuous light, but decreased under continuous dark. Knockdown of Hp-ecpn mRNA using morpholino antisense oligonucleotides decreased the number of ECPN cells considerably, and inhibited the vertical swimming of the larvae. This suggested that Hp-ECPN plays a role in photosensitive larval swimming vertical migration. In adult tissues, the ECPN cells were detected exclusively in tube feet.

Sea urchin tube feet are photosensory organs that express a rhabdomeric-like opsin and PAX6

“…It has been hypothesized that melanopsin sets the circadian clock through non-ocular light detection [52], and is also expressed in sea urchins [30]. Additionally, an encephalopsin homologue has been sequenced from sea urchins [30,41], which is expressed at the tips of the larval arms of plutei and tube feet of adults [16,41], and potentially aids in the detection of light by planktonic larvae vertically migrating in the water column. The inverse relationship between tube foot position on the test, which equates to differences in light exposure, and expression of the green sea urchin rhabdomeric-like opsin, is phenomenologically similar to the well-known inverse relationship between light and photosynthetic pigments universally expressed from microalgae to higher plants.…”

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

“…They are the neuronal mesenchyme cells (NMC) that were initially introduced as the tertiary mesenchyme cells, 4 which were discovered to be new group of mesenchymal cells in the last couple of years. However, because the cells are characterized by the expression of neuronal genes or proteins, such as glutamate decarboxylase [GAD; g-aminobutyric acid (GABA) synthetase], serotonin receptors 4 and encephalopsin, 5 they are called NMCs in this Review. The morphogenetic analysis of PMC formation has been incorporated in sea urchin developmental biology as a classical model of the EMT (Fig.…”

“…Two of 3 NMC genes, Hp-ecpn 6 and Hp-gad, 5 are expressed in the ectoderm as early as the 15-hpf swimming blastula stage until at least the 2-arm pluteus stage in H. pulcherrimus. The Hp-ECPN expressing cells (ECPN cells) plays an essential role in photoresponsive larval swimming.…”

“…The Hp-ECPN expressing cells (ECPN cells) plays an essential role in photoresponsive larval swimming. 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.…”

Development of a dopaminergic system in sea urchin embryos and larvae

“…The swimming of marine larvae depends on ciliary propulsion and is critically important for feeding, escape responses (Strathmann, 2007;Stephens, 2008) and photosensitive vertical migration (Ooka et al, 2010). In sea urchin embryos, motile cilia are evident from the blastula stage, and rotatory movement by embryos can be observed in the fertilization envelope.…”