Hovering between death and life: Natural apoptosis and phagocytes in the blastogenetic cycle of the colonial ascidian Botryllus schlosseri

Immune roles of a rhamnose-binding lectin in the colonial ascidian Botryllus schlosseri

“…We have already demonstrated that about 20-30% of circulating haemocytes undergo cell death during TO: the BsRBL-immunopositive haemocytes with labelled cell surfaces observed during this phase of the colonial blastogenetic cycle probably correspond to senescent cells, and labelling of their surfaces by BsRBL may represent an "eat me" signal, for clearance of these cells by phagocytes. The above-noted increase in BsRBL expression at TO is probably required to enhance phagocytosis of the effete cells of senescent zooids during this crucial phase of the colonial blastogenetic cycle, which (Cima et al 2003(Cima et al , 2010Ballarin et al 2008a). In addition, the lectin induces the release of molecules recognised by antibodies raised against mammalian IL1␣ and TNF␣, which act as immunomodulatory molecules, i.e., cytokines Menin and Ballarin 2008) and are involved in typical inflammatory responses such as the non-fusion reaction between contacting, genetically incompatible colonies (Cima et al 2004).…”

“…Each blastogenetic cycle ends with the generation change or take-over (TO), during which the zooids close their siphons and are gradually resorbed and replaced by a new generation of adult zooids, represented by buds which reach functional maturity, open their siphons, and begin filtering activity; in the meantime, a new generation of zooids originates from the body wall of the buds (Berrill 1941;Sabbadin 1955;Lauzon et al 1992). The TO is characterised by massive cell death by apoptosis in tissues of regressing zooids (Lauzon et al 1992(Lauzon et al , 1993Ballarin et al 2008aBallarin et al ,b, 2010Cima and Ballarin 2009). Colonial developmental stages lying more than one day from the preceding and following TO, are referred to as mid-cycle stages (Lauzon et al 1992;Manni et al 2007).…”

Characterization of Ambra1 in asexual cycle of a non-vertebrate chordate, the colonial tunicate Botryllus schlosseri, and phylogenetic analysis of the protein group in Bilateria

“…It is also to note that in B. schlosseri autophagic vacuoles were evidenced at transmission electron microscope during the take-over (Burighel and Milanesi, 1973;Burighel and Schiavinato, 1984). Taking into account that this colonial stage is dominated by apoptosis in adult zooids (Cima et al, 2010) and that Ambra1 in mammals contributes to apoptosis regulation (Fimia et al, 2007), it will be interesting to evaluate which is the role of Ambra1 during this critical colonial stage.…”

“…During the regression phase, adult organs undergo shrinkage and collapse, circulating phagocytes massively infiltrate senescent tissues and rapidly ingest apoptotic cells (Burighel and Schiavinato, 1984). Within 24-36 h, zooids are completely resorbed (Ballarin et al, 2008;Cima et al, 2010). Since a colony is virtually immortal, many cyclical apoptotic events occur during its life span: for this reason, B. schlosseri is considered a useful model to study programmed cell death.…”

Routes in Innate Immunity Evolution: Galectins and Rhamnose‐binding Lectins in Ascidians

“…The rise in the frequency of immunopositive cells at take-over is probably related to the massive apoptosis occurring in the tissues of old zooids during this phase of the colonial blastogenetic cycle. Previous studies (Cima et al, 2010) indicate that phagocytes change their morphology and behavior during the take-over, and 20-30% of circulating hemocytes undergo cell death. Therefore, the increase in immunolabeled cells probably has a twofold origin, deriving both from the increase in the number of phagocytes synthesizing BsRBL, which justifies the higher quantity of lectin mRNA at take-over, and in part from the interaction of BsRBL with the surfaces of senescent cells, as coating by BsRBL may either induce apoptosis in effete cells expressing complementary glycolipids, analogously to what is reported for catfish-egg RBL (Kawano et al, 2009;Shirai et al, 2009), or represent an 'eat me' signal for the clearance of dying cells by phagocytes.…”