The haemocytes of the colonial aplousobranch ascidian Diplosoma listerianum: Structural, cytochemical and functional analyses

Abstract

Diplosoma listerianum is a colonial aplousobranch ascidian of the family Didemnidae that is native to the northeast Atlantic and exhibits a cosmopolitan distribution in temperate waters. It lacks a shared colonial circulation crossing the tunic, and the zooids are connected only by the common tunic. In the present study, the haemocytes of this ascidian were analysed via light and electron microscopy. Their phagocytic and enzymatic activities, staining and immunostaining properties, and lectin affinity were examined with various classical methods reconsidered and modified for small marine invertebrates. Eight morphotypes were identified in reference to corresponding cell types described in other ascidians: undifferentiated cells (haemoblasts), storage cells for nitrogenous catabolites (nephrocytes) and immunocytes. The immunocytes are involved in immune responses, acting as (1) phagocytes, rich in hydrolases and involved in the clearance of both foreign particles and effete cells (hyaline amoebocytes and macrophage-like cells); (2) cytotoxic cells, able to degranulate and induce cytotoxicity through the release of the enzyme phenoloxidase after an immune stimulus (granular amoebocytes and morula cells); and (3) basophilic cells with an affinity for ConA and NPA that contain heparin and histamine and that show sensitivity to the compound 48/80, promoting their degranulation (mast cell-like granulocytes). In addition, a particular cell type showing exceptional development of the Golgi apparatus and large vacuoles containing a filamentous material has been recognised (spherule cell), for which a role in tunic repair and fibrogenesis has been hypothesised.

Novel budding mode in Polyandrocarpa zorritensis: a model for comparative studies on asexual development and whole body regeneration

“…3e, f) [50]. Later during bud development, the membranes of these ampullar cells disintegrate, while they are in close contact with numerous hemocytes resembling morula cells [26, 51, 52]. Morula cells have been proposed as cytotoxic cells based on their phenoloxidase activity in different styelid species [53].…”

Features of a novel protein, rusticalin, from the ascidian Styela rustica reveal ancestral horizontal gene transfer event

“…About 40% of the blood cells in the ascidian Styela rustica are represented by hyalinocytes [22]. Hyalinocytes or their equivalents in other ascidian species perform functions such as phagocytosis [22, 27], cytokine synthesis [34], and protease release upon LPS induction [28]. In order to isolate the rusticalin protein of hyalinocytes and describe its gene, we conducted MALDI and RACE.…”

“…Accordingly, all rusticalin-like proteins are predicted by TargetP to be secretory. The fact that rusticalin is specific to hyalinocytes does not contradict its putative immune function since at least hyaline amoebocytes are also known to be capable of phagocytosis [27]. Another protein previously characterized as Zn-dependent metallo-protease from the ascidian Halocynthia roretzi hemocytes is activated by lipopolysaccharide (LPS) [28, 43, 44] and hence might also be involved in immune reactions.…”

“…Apart from epidermal cell layer tunic formation involves also blood cells [22, 23]. Several morphotypes of blood cells have been described for ascidians [22, 24–27], including hyalinocytes. In the blood of a solitary ascidian Styela rustica hyalinocytes and morula cells are two dominating cell groups, with an average abundance of 38 and 56%, respectively [22].…”

<p>Current Knowledge on Stem Cells in Ascidians</p>

“…The description of the ascidian haemocytes shows considerable variations among species and may exhibit 5-11 morphologically distinguishable cell types (Nette et al 1999;Hartenstein 2006;Arizza and Parrinello 2009;Blanchoud et al 2017;Cima et al 2017;. Therefore, to gain comparable information on the differing glycans of blood cells, we adopted a common standard for the haemocyte classification in ascidians, with three main groups: haemoblasts, immunocytes, and storage cells (Figure 1).…”