Nervous System Development and Neuropeptides Characterization in Embryo and Larva: Insights from a Non-Chordate Deuterostome, the Sea Cucumber Apostichopus japonicus

Abstract

Here, we described the complex nervous system at five early developmental stages (blastula, gastrula, auricularia, doliolaria and pentactula) of a holothurian species with highly economic value, Apostichopus japonicus. The results revealed that the nervous system of embryos and larvae is mainly distributed in the anterior apical region, ciliary bands or rings, and the feeding and attachment organs, and that serotonergic immunoreactivity was not observed until the embryo developed into the late gastrula; these are evolutionarily conserved features of echinoderm, hemichordate and protostome larvae. Furthermore, based on available transcriptome data, we reported the neuropeptide precursors profile at different embryonic and larval developmental stages. This analysis showed that 40 neuropeptide precursors present in adult sea cucumbers were also identified at different developmental stages of embryos and larvae, and only four neuropeptide precursors (SWYG precursor 2, GYWKDLDNYVKAHKT precursor, Neuropeptide precursor 14-like precursor, GLRFAmprecursor-like precursor) predicted in adults were absent in embryos and larvae. Combining the quantitative expression of ten specific neuropeptide precursor genes (NPs) by qRT-PCR, we revealed the potential important roles of neuropeptides in embryo development, feeding and attachment in A. japonicus larvae. In conclusion, this work provides novel perspectives on the diverse physiological functions of neuropeptides and contributes to understanding the evolution of neuropeptidergic systems in echinoderm embryos and larvae.

Sea cucumbers: an emerging system in evo-devo

“…Studies based on immunohistochemical detection of the echinoderm specific pan-neuronal marker Synaptotagmin B in sea cucumbers showed that the first neurons appear at the late gastrula stage in the anterior neuroectoderm domain [ 22 , 110 , 178 ] (Fig. 4 ).…”

“…The holothurian nervous system complexity increases as development continues and neurons are fully differentiated at the feeding auricularia stage. The auricularia nervous system consists of serotonergic ganglia located in the apical organ and neurons distributed along the ciliary band and in close proximity to the esophagus, intestine and anus [ 27 , 110 , 178 ]. Although the overall nervous system organization of holothurians is similar to echinoids and asteroids, several differences have been reported (Fig.…”

“…A great diversity of neuropeptides is detected while the auricularia feeds and grows, suggesting their involvement in feeding behavior and larval growth [ 178 ]. At this stage, neuropeptides with a role in feeding control in other organisms are present, such like orexin, insulin-like and SALFamide neuropeptides [ 178 ]. Less is known about the nervous system organization in the doliolaria and pentactula stages.…”

The Isolation, Purification and Active Mechanism of Sea Cucumber Bone-Strengthening Functional Peptides

“…Thyroid hormone PTH is a commonly used peptide composed drug for bone-related conditions such as osteoporosis [15].RANK/RANKL is a relevant pathway of bone metabolism has a direct role in relation to bone synthesis [30]. Integrin AVB3 and integrin α5β are commonly used integrin receptors associated with osteoblast proliferation.…”

Chromosomal-level genome assembly of the long-spined sea urchinDiadema setosum(Leske, 1778)

“…Owing to its critical phylogenetic position, sea urchin offers the understanding of how deuterostomes evolved (e.g. Odekunle et al, 2019; Yañez-Guerra et al, 2020; Sakai et al, 2020; Logeswaran et al 2021; Zheng et al, 2022). To date, 16 sea urchin genomes are available according to the data presented on NCBI (25 October 2023) and only five of them (all in the order Camarodonta) are assembled in chromosomal level ( Lytechinus variegatus (Davidson et al, 2020), Lytechinus pictus (Warner et al, 2021), Heliocidaris erythrogramma (Davidson et al, 2022), Heliocidaris tuberculata (Davidson et al, 2022) and Echinometra lucunter (Davidson et al, 2023).…”