Discovery and functional characterization of neuropeptides in crinoid echinoderms

Abstract

Neuropeptides are one of the largest and most diverse families of signaling molecules in animals and, accordingly, they regulate many physiological processes and behaviors. Genome and transcriptome sequencing has enabled the identification of genes encoding neuropeptide precursor proteins in species from a growing variety of taxa, including bilaterian and non-bilaterian animals. Of particular interest are deuterostome invertebrates such as the phylum Echinodermata, which occupies a phylogenetic position that has facilitated reconstruction of the evolution of neuropeptide signaling systems in Bilateria. However, our knowledge of neuropeptide signaling in echinoderms is largely based on bioinformatic and experimental analysis of eleutherozoans—Asterozoa (starfish and brittle stars) and Echinozoa (sea urchins and sea cucumbers). Little is known about neuropeptide signaling in crinoids (feather stars and sea lilies), which are a sister clade to the Eleutherozoa. Therefore, we have analyzed transcriptome/genome sequence data from three feather star species, Anneissia japonica, Antedon mediterranea, and Florometra serratissima, to produce the first comprehensive identification of neuropeptide precursors in crinoids. These include representatives of bilaterian neuropeptide precursor families and several predicted crinoid neuropeptide precursors. Using A. mediterranea as an experimental model, we have investigated the expression of selected neuropeptides in larvae (doliolaria), post-metamorphic pentacrinoids and adults, providing new insights into the cellular architecture of crinoid nervous systems. Thus, using mRNA in situ hybridization F-type SALMFamide precursor transcripts were revealed in a previously undescribed population of peptidergic cells located dorso-laterally in doliolaria. Furthermore, using immunohistochemistry a calcitonin-type neuropeptide was revealed in the aboral nerve center, circumoral nerve ring and oral tube feet in pentacrinoids and in the ectoneural and entoneural compartments of the nervous system in adults. Moreover, functional analysis of a vasopressin/oxytocin-type neuropeptide (crinotocin), which is expressed in the brachial nerve of the arms in A. mediterranea, revealed that this peptide causes a dose-dependent change in the mechanical behavior of arm preparations in vitro—the first reported biological action of a neuropeptide in a crinoid. In conclusion, our findings provide new perspectives on neuropeptide signaling in echinoderms and the foundations for further exploration of neuropeptide expression/function in crinoids as a sister clade to eleutherozoan echinoderms.

A feather star is born: embryonic development and nervous system organization in the crinoidAntedon mediterranea

“…It has been shown previously that the pentacrinoid nervous system comprises a complex basiepithelial net of serotonergic, GABAergic and peptidergic neurons, concentrated at the level of the tube feet, and a conspicuous entoneural system comprising cholinergic and peptidergic cells [4, 27]. Immunoreactivity for ß-tubulin showed that the post-metamorphic system was highly interconnected, with five bundles of fibers directing from the entoneural aboral nerve centre to a circumoral nerve ring, which was in turn connected to fibers that run in the tube feet (Fig.…”

“…It has been shown previously that the pentacrinoid nervous system comprises a complex basiepithelial net of serotonergic, GABAergic and peptidergic neurons, concentrated at the level of the tube feet, and a conspicuous entoneural system comprising cholinergic and peptidergic cells [4,27].…”

“…After a short larval phase, the doliolaria settles on the seabed and undergoes a gradual metamorphosis, during which the larval tissues are rearranged to form a transient cystidean stage that develops into a sessile pentacrinoid [17, 26, 4]. The majority of recent studies on crinoid development have focused on post-embryonic stages [22, 23, 27], while the molecular cues guiding embryogenesis still remain mostly unexplored. This is partly due to difficulties in collecting wild specimens and in manipulating crinoid gametes and embryos.…”

Relaxin-like Gonad-Stimulating Peptides in Asteroidea

“…RGP and ISL are present not only in starfish (class Asteroidea), but also in other echinoderms such as sea urchins (class Echinoidea) [33], sea cucumbers (class Holothuroidae) [34,35], brittle stars (class Ohiuroidea) [36], and sea lilies (class Crinoidea) [37]. It was revealed that sea cucumber RGP induces gamete shedding in Holothuria scabra and H. leucospilota [35].…”

Localization of relaxin‐like gonad‐stimulating peptide expression in starfish reveals the gonoducts as a source for its role as a regulator of spawning

“…A. solaris (Mita, Ikeda, et al., 2015 ; Smith et al., 2019 ), Aphelasterias japonica (Mita & Katayama, 2016 ), Asterias rubens (Lin, Mita, et al., 2017 ; Semmens et al., 2016 ), and Astropecten scoparius (Mita, Osugi, et al., 2021 ), revealing evolutionary conservation of both its structure and function. Relaxin‐type peptide precursors have also been identified in other echinoderms, including ophiuroids (brittle stars), holothurians (sea cucumbers), and crinoids (feather stars) (Aleotti et al., 2022 ; Chieu et al., 2019 ; Suwansa‐Ard et al., 2018 ; Zandawala et al., 2017 ). Furthermore, a relaxin‐type peptide triggers spawning in the sea cucumber Holothuria scabra , showing that the gonadotropic action of relaxin‐type peptides also extends to other echinoderms (Chieu et al., 2019 ).…”