Starfish ApDOCK protein essentially functions in larval defense system operated by mesenchyme cells

Ethical Considerations for Echinoderms: New Initiatives in Welfare

This paper explores the ethical considerations surrounding research on echinoderms, a group of invertebrates that has recently garnered attention in the scientific community. The importance of responsible animal handling and the need for an ethical framework that encompasses echinoderms are emphasized. The 3Rs principle, advocating for the replacement of conscious living vertebrates with non-sentient material in research, is discussed as a guiding tool in current animal research practices. As invertebrates are generally classified as non-sentient animals, the replacement dimension tends to favor them as prevalent models in experimental research. While it currently lacks the means to assess the mental states of invertebrates, there is undeniable evidence of social behavior in many species, suggesting that a lack of interactions with these organisms could potentially adversely affect their wellbeing. In the last few years, considerable progress has been made in developing an ethical framework that takes invertebrates into account, particularly cephalopods, crustaceans, and echinoderms. In this context, we discuss the development of a broader conceptual framework of 5Rs that includes responsibility and respect, which may guide practices ensuring welfare in echinoderms, even in the absence of any particular normative.

Analysis of immune response in the sea urchin larva

Sea urchin larvae deploy a complex immune system in the context of relatively simple morphology. Several types of phagocytic or granular immune cells respond rapidly to microbes and microbial components within the body cavity. Many of these cells also respond to microbial disturbances in the gut lumen. In the course of immune response, hundreds of genes are up- and downregulated, many of which have homologs involved in immunity in other species. Thus, the larval sea urchin provides an experimentally advantageous model for investigating the response to immune challenge at the level of cell behavior and gene regulatory networks. Importantly, the morphological simplicity and optical clarity of these larvae allow studies to be carried out within the intact animal. Here, we outline techniques to probe and visualize the immune system of the feeding sea urchin larva, particularly for quantifying gene expression and cell migration as the animal responds to both pathogens and symbionts. Techniques addressed in this chapter include (1) exposure of larvae to microbes and microbial products in sea water and by blastocoelar microinjection, (2) time-lapse imaging of immune response, (3) isolation of culturable bacteria associated with feeding larvae, (4) quantification of larval associations with isolated bacterial strains and (5) preparation of secreted products from isolated bacteria for testing in larval culture.

Two macrophage migration inhibitory factors regulate starfish larval immune cell chemotaxis

Immune cell recruitment is critical step in the inflammatory response and associated diseases. However, the underlying regulatory mechanisms are poorly understood in invertebrates. Mesenchyme cells of the starfish larvae, which allowed Metchnikoff to complete his landmark experiments, are important model for analysis of immune cell migration. The present study investigated the role of macrophage migration inhibitory factor (MIF)--an evolutionarily conserved cytokine that is functionally similar to chemokines--in the larvae of the starfish Patiria (Asterina) pectinifera, which were found to possess two orthologs, ApMIF1 and ApMIF2. ApMIF1 and ApMIF2 clustered with mammalian MIF and its homolog D-dopachrome tautomerase (DDT), respectively, in the phylogenetic analysis. In contrast to the functional similarity between mammalian MIF and DDT, ApMIF1 knockdown resulted in the excessive recruitment of mesenchyme cells in vivo, whereas ApMIF2 deficiency inhibited the recruitment of these cells to foreign bodies. Mesenchyme cells migrated along a gradient of recombinant ApMIF2 in vitro, whereas recombinant ApMIF1 completely blocked ApMIF2-induced directed migration. Moreover, the expression patterns of ApMIF1 and ApMIF2 messenger RNA in bacteria-challenged mesenchyme cells were consistent with in vivo observations of cell behaviors. These results indicate that ApMIF1 and ApMIF2 act as chemotactic inhibitory and stimulatory factors, respectively, and coordinately regulate mesenchyme cell recruitment during the immune response in starfish larvae. This is the first report describing opposing functions for MIF- and DDT-like molecules. Our findings provide novel insight into the mechanisms underlying immune regulation in invertebrates.