Relationships among hemocytes, tunic cells, germ cells, and accessory cells in the colonial ascidian Botryllus schlosseri

Abstract

Monoclonal antibodies were raised against hemocytes of the colonial ascidian Botryllus schlosseri as possible tools to study hemocyte differentiation. In this species, blood cells are involved in various biological functions, such as immunosurveillance, encapsulation of foreign bodies, metal accumulation, and allorecognition. The latter process drives the fusion or rejection of contacting colonies, according to whether they do or do not share at least one allele at the fusibility/histocompatibility (Fu/HC) locus. Hemocytes take part in the rejection reaction, which suggests that they express molecules, coded by the Fu/HC locus, on their surface. A homozygous colony at the Fu/HC locus was used to produce the antibodies, which were screened by immunocytochemistry on hemocyte monolayers, immunohistochemistry on colony paraffin sections, and immunoblotting on colony homogenates. Here, we report on one of the obtained antibodies (1D8), which recognized a surface epitope on hemocytes of the donor colony and other colonies, apparently in a manner specific to the Fu/HC genotype. It also labeled a single 80-kDa band in colony homogenates. In addition, it specifically recognized tunic cells, germ cells, and their accessory cells. These results strengthen the assumption of a close relationship among these types of cells and blood cells, and suggest a close relationship among the above cells, probably deriving from undifferentiated blood cells.

Hematological Analysis of the Ascidian Botrylloides leachii (Savigny, 1816) During Whole-Body Regeneration

“…The identified cell types are compatible with previous reports in this species (Cima et al, 2002), comparable to those in other ascidians (Cima et al, 2014) and in particular to those of the same family (Styelidae; Ballarin and Kawamura, 2009;de Barros et al, 2009;Gutierrez and Brown, 2017). Notably, while granular cells appear to be absent from other botryllid species (Hirose et al, 2003;Ballarin et al, 2011), they have been identified in Styela plicata (de Barros et al, 2009), Symplegma brakenhiemli (Gutierrez and Brown, 2017) and even in Thalia democratica (Cima et al, 2014). Their presence in more distant species of ascidians suggests either a loss in botryllids that did not affect B. leachii or that their visual characteristics are not observable in these botryllids.…”

Sexual and asexual reproduction in the colonial ascidian Botryllus schlosseri

“…Studies on self-and cross-fertilization declined in the 1970s but still offered cues regarding the successive investigations on the reproduction of B. schlosseri, primarily addressing the study of the morphology of the gonads and gametes (Burighel and Martinucci, 2000;Burighel et al, 1982;Manni et al, 1993Manni et al, , 1994Sabbadin and Zaniolo, 1979), the success of fertilization in relation to population density and sperm release (Johnson and Yund, 2004;Phillippi et al, 2004;Stewart-Savage et al, 2001;Stewart-Savage and Yund, 1997), placentation (Zaniolo et al, 1987), germ cell recognition and migration (Ballarin et al, 2011;Brown et al, 2009;Rinkevich et al, 2013;Rosner et al, 2013;Sabbadin and Zaniolo, 1979).…”

Histological and haematological analysis of the ascidianBotrylloides leachii(Savigny, 1816) during whole-body regeneration

“…By combining previous classification schemes for botryllid ascidians (Ballarin et al, 2011; Ballarin and Cima, 2005; Cima et al, 2002; Hirose et al, 2003), we propose a generalized classification of B . leachii circulatory haemocytes into five functional groups: undifferentiated cells, immunocytes, mast cell-like cells, transport cells and storage cells (Table 1).…”

“…We additionally characterised the morphological and haematological modulation of injured colonies throughout WBR. Morula cells are known constituents of the immune system involved in inflammatory responses, haemolymph clotting, homeostasis, and tunic repair (Ballarin et al, 2011, 2001; de Leo, 1992; Menin et al, 2005). The large number of infiltrated morula cells observed during stage 1 of WBR highlights a need for both clearance of decaying or foreign debris and reorganization of the injured vascular system during the first 15 h post dissection.…”

“…Although there has been a number of studies investigating the morphotypes of ascidian haemocytes (Ballarin et al, 2011; Ballarin and Cima, 2005; de Leo, 1992; Endean, 1960; Freeman, 1964; Hirose et al, 2003; Wright and Ermak, 1982), including offi leachii’s (Cima et al, 2002), improved resolution and colour images would benefit future work on this species. In addition, no common terminology has been accepted to identify these cell types, mainly because of discrepancies between their phenotype and their function in different species, as well as a lack of understanding of their differentiation lineages (Ballarin et al, 2011; Cima et al, 2002; Endean, 1960; Freeman, 1964; Goodbody, 1975; Millar and Ratcliffe, 1989; Wright, 1981). Furthermore, accurate identification is crucial for detecting and interpreting variations in the sub-populations of haemocytes during WBR.…”