Movement and storage of nematocysts across development in the nudibranch Berghia stephanieae (Valdés, 2005)

Abstract

Background Intracellular sequestration requires specialized cellular and molecular mechanisms allowing a predator to retain and use specific organelles that once belonged to its prey. Little is known about how common cellular mechanisms, like phagocytosis, can be modified to selectively internalize and store foreign structures. One form of defensive sequestration involves animals that sequester stinging organelles (nematocysts) from their cnidarian prey. While it has been hypothesized that nematocysts are identified by specialized phagocytic cells for internalization and storage, little is known about the cellular and developmental mechanisms of this process in any metazoan lineage. This knowledge gap is mainly due to a lack of genetically tractable model systems among predators and their cnidarian prey. Results Here, we introduce the nudibranch Berghia stephanieae as a model system to investigate the cell, developmental, and physiological features of nematocyst sequestration selectivity. We first show that B. stephanieae, which feeds on Exaiptasia diaphana, selectively sequesters nematocysts over other E. diaphana tissues found in their digestive gland. Using confocal microscopy, we document that nematocyst sequestration begins shortly after feeding and prior to the formation of the appendages (cerata) where the organ responsible for sequestration (the cnidosac) resides in adults. This finding is inconsistent with previous studies that place the formation of the cnidosac after cerata emerge. Our results also show, via live imaging assays, that both nematocysts and dinoflagellates can enter the nascent cnidosac structure. This result indicates that selectivity for nematocysts occurs inside the cnidosac in B. stephanieae, likely in the cnidophage cells themselves. Conclusions Our work highlights the utility of B. stephanieae for future research, because: (1) this species can be cultured in the laboratory, which provides access to all developmental stages, and (2) the transparency of early juveniles makes imaging techniques (and therefore cell and molecular assays) feasible. Our results pave the way for future studies using live imaging and targeted gene editing to identify the molecular mechanisms involved in nematocyst sequestration. Further studies of nematocyst sequestration in B. stephanieae will also allow us to investigate how common cellular mechanisms like phagocytosis can be modified to selectively internalize and store foreign structures.

A chromosome-level genome for the nudibranch gastropodBerghia stephanieaehelps parse clade-specific gene expression in novel and conserved phenotypes

“…4A-A'''). This may be due to the fact that nematocyst sequestration relies on a largely conserved process, namely phagocytosis [36,41,67]. Our results also did not show a higher proportion clade-specific genes upregulated in the sensory rhinophores or oral tentacles compared to other tissues, which are functionally similar and homologous to tentacles in other heterobranch gastropods and caenogastropods [34,68,69].…”

“…In order to confirm the expression of clade-specific genes inferred to be upregulated in certain tissues, we localized expression of at least one gene from each of two tissues (rhinophores and distal ceras) using in situ Hybridization Chain Reaction (HCR) techniques [50] in Berghia juveniles. We also compared our list of genes upregulated in the Berghia brain to HCR gene expression profiling in the brain of adult Berghia available from Ramirez et al [51] Juveniles were selected for our experiments because adult Berghia contain pigments that make localizing expression more difficult, and both the distal ceras and rhinophores are identifiable and functional at an early juvenile stage [34, 36]. We localized a distal ceras upregulated Nudibranchia-specific gene (jg13556; annotated as collagen alpha-1, match to UniProt ID Q7LZR2, e-value = 0.000129) in juvenile distal cerata (Fig.…”

“…Berghia stephanieae (hereafter referred to as Berghia ) is a species of gastropod in the order Nudibranchia, a clade of marine slugs that lose their shell during metamorphosis [33]. This species has been used as a model for the study of both more conserved systems, such as neurodevelopment [34] and reproductive development [35], as well as clade-restricted phenotypes such as the sequestration of cnidarian nematocysts [36, 37] and endosymbiosis [38, 39]. We combined an inferred proteome from Berghia with available genome and transcriptome data from other metazoan species – including mollusks such as cephalopods, bivalves, and other gastropods – to identify clade-specific Berghia genes (i.e., restricted to Mollusca, Gastropoda, Heterobranchia, Nudibranchia, Aeolidina, or Berghia alone).…”

Nematocyst sequestration within the family Fionidae (Gastropoda: Nudibranchia) considering ecological properties and evolution

“…Eubranchus rupium and Tergipes tergipes ), have different musculature layer thicknesses. Variation of the musculature thickness may be explained by the differences in the developmental stages of studied specimens, as was shown recently for Berghia stephanieae [ 66 ]. However, all molluscs studied here were fully mature (specimens of each species commonly copulated with each other) to avoid possible ontogenetic variation.…”

Precocious Sperm Exchange in the Simultaneously Hermaphroditic Nudibranch,Berghia stephanieae

“…1974 ; Chase 2002 ; Katz and Quinlan 2019 ), nematocyst sequestration ( Goodheart and Bely 2017 ; Goodheart et al. 2018 , 2022 ), and reproduction ( Rutowski 1983 ; Rivest 1984 ; Hall and Todd 1986 ; Sekizawa et al. 2019 ).…”