Neuropeptide expression in the box jellyfish Tripedalia cystophora—New insights into the complexity of a “simple” nervous system

Abstract

Box jellyfish have an elaborate visual system and perform advanced visually guided behaviors. However, the rhopalial nervous system (RNS), believed to be the main visual processing center, only has 1000 neurons in each of the four eye carrying rhopalia. We have examined the detailed structure of the RNS of the box jellyfish Tripedalia cystophora, using immunolabeling with antibodies raised against four putative neuropeptides (T. cystophora RFamide, VWamide, RAamide, and FRamide). In the RNS, T. cystophora RF-, VW-, and RAamide antibodies stain sensory neurons, the pit eyes, the neuropil, and peptide-specific subpopulations of stalk-associated neurons and giant neurons. Furthermore, RFamide ir+ neurites are seen in the epidermal stalk nerve, whereas VWamide antibodies stain the gastrodermal stalk nerve. RFamide has the most widespread expression including in the ring and radial nerves, the pedalium nerve plexus, and the tentacular nerve net. RAamide is the putative neurotransmitter in the motor neurons of the subumbrellar nerve net, and VWamide is a potential marker for neuronal differentiation as it is found in subpopulations of undifferentiated cells both in the rhopalia and in the bell. The results from the FRamide antibodies were not included as only few cells were stained, and in an unreproducible way. Our studies show hitherto-unseen details of the nervous system of T. cystophora and allowed us to identify specific functional groups of neurons. This identification is important for understanding visual processing in the RNS and enables experimental work, directly addressing the role of the different neuropeptides in vision.

Expression of Opsins of the Box Jellyfish Tripedalia cystophora Reveals the First Photopigment in Cnidarian Ocelli and Supports the Presence of Photoisomerases

“…The opsins investigated in this study were originally identified from transcriptomics of juvenile and adult medusae of T. cystophora (Nielsen et al, 2019). Specific antibodies against three of the recovered opsins were produced in rabbits (Genosphere, Paris, France) using the following three amino acid sequences from their c-terminus:…”

“…In this study, we raised antibodies against the three unidentified opsins recently discovered in transcriptomic data from the Caribbean cubozoan, Tripedalia cystophora (Nielsen et al, 2019). We used these antibodies to examine expression not only in polyps and medusae of T. cystophora but also in the hydromedusa, in Sarsia tubulosa, and in the ocellus-carrying rhopalia of the scyphomedusae Aurelia aurita and Cassiopea xamachana.…”

Comparative investigations of cellular dynamics in the development of medusae (Cnidaria: Medusozoa)

“…The rhopalium is a tentacle-derived hollow structure bearing statocysts and photoreceptors and is found only in Acraspeda (Berrill,1949). Cubozoans also have a single nerve ring in the bell in cubozoans (Garm et al, 2006, Nielsen et al, 2021).…”

Neural Cell Type Diversity in Cnidaria

“…The rhopalium contains two lens eyes, as well as two pairs of simpler pit eyes and a statocyst ( Nilsson et al, 2005 ). Anatomical studies in Tripedalia cystophora showed that the rhopalial nervous system contains over 1,000 neurons, which can be further divided into several morphologically different cell types, some defined by the expression of neuropeptides ( Nielsen et al, 2021 ). While architecture of the neural circuits remains still largely unknown it has been shown that Tripedalia cystophora use visual cues from the surrounding world to alter its swimming behavior and thereby navigates in mangrove areas by using terrestrial cues seen through the water surface ( Petie et al, 2011 ; Garm et al, 2012 ).…”

“…While architecture of the neural circuits remains still largely unknown it has been shown that Tripedalia cystophora use visual cues from the surrounding world to alter its swimming behavior and thereby navigates in mangrove areas by using terrestrial cues seen through the water surface ( Petie et al, 2011 ; Garm et al, 2012 ). The example of the rhopalial nervous system of cubozoans shows that in certain cnidaria species the nervous system may have evolved structures that are much more complex than the widely assumed simple nerve net ( Petie et al, 2011 ; Garm et al, 2012 ; Nielsen et al, 2021 ). While one may argue that medusae have an overall more complex lifestyle since they are freely swimming, also the behavioral capacity of polyps may be more complicated than naively expected.…”