Tail regression inCiona intestinalis(Prochordate) involves a Caspase-dependent apoptosis event associated with ERK activation

Abstract

Two apoptotic events take place during embryonic development of Ciona intestinalis. The first concerns extra-embryonic cells and precedes hatching. The second controls tail regression at metamorphosis, occurs through a polarized wave originating from tail extremity, and is caspase dependent. This was shown by: (1) in vivo incorporation of a fluorescent marker of caspase activation in different cell types of the tail; (2) detection of an activated form of caspase 3-like protein by western blotting; and (3) failure of 30% of larvae to undergo metamorphosis after treatment of fertilized eggs with a pan-caspase inhibitor. In addition, Ciona embryos express a single ERK protein, specifically phosphorylated at metamorphosis. ERK activation was shown to be located in cells of the tail. Addition of MEK inhibitor in the culture medium prevented ERK activation and metamorphosis. In silico analysis of Ciona genome pointed to 15 caspases with high homology with humans, and a single ERK gene with high homology to both mammalian ERK1 and ERK2. It is concluded that the sequence of events leading to metamorphosis includes ERK phosphorylation followed by caspase-dependent apoptosis and tail regression. Movies available on-line

Identification, Characterization, and Expression Analysis Reveal Diverse Regulated Roles of Three MAPK Genes in Chlamys farreri Under Heat Stress

“…CfERK maintained a relatively high level from D-shaped larvae to juvenile stages, indicating that it may be involved in the organ development and metamorphic process of C. farreri larvae, such as the disappearance of the velizer, the development of the gills and foot, and the formation of the secondary shell. In previous researches, the expression of ERK was essential for the tail degeneration of C. intestinalis (Chambon et al, 2002). During zebrafish embryonic development, ERK was activated by fibroblast growth factor (FGF), and it could regulate the development and formation of organs, including eye, somites, and limbs (Wong et al, 2019).…”

JNK Mediates Differentiation, Cell Polarity and Apoptosis During Amphioxus Development by Regulating Actin Cytoskeleton Dynamics and ERK Signalling

“…In contrast, in the solitary ascidian Ciona, programmed cell death is necessary for regression of the tadpole tail and settlement (Krasovec et al, 2019). Here, signalling by both ERK and JNK MAP kinases is required (Chambon et al, 2007), and tail regression fails when either the pathway is inhibited, or Caspase activity is blocked (Chambon et al, 2002;Krasovec et al, 2019).…”

Comparative transcriptomic analysis reveals gene regulation mediated by caspase activity in a chordate organism

“…In this report, we took advantage of the predictable spatiotemporal apoptotic profile of ascidians [21,22], in particular during the Ciona intestinalis metamorphosis, which is concomitant with cell survival and cell migration [21,23,24]. Ciona belongs to the Urochordata, the sister group of vertebrates [25], and has a biphasic life cycle composed of a pelagic larva and a benthic adult.…”

“…Embryogenesis generates a tadpole-like swimming larva consisting of an anterior trunk and a posterior tail which, after few hours of swimming, settles and metamorphoses into a sessile juvenile. A hallmark of metamorphosis is the apoptotic-dependent tail regression [21] during which apoptosis starts at the tip of the tail and propagates toward the trunk, making it easily anticipated; a unique feature among chordates. Using TUNEL labelling and electron microscopy, we previously described in detail this apoptotic profile.…”

“…To identify genes controlled by caspases activity during tail regression, we performed a comparative transcriptomic analysis at the beginning and at mid-tail regression between control metamorphosing larvae or larvae exposed to the pan-caspase inhibitor Z-VAD-fmk, already successfully used in Ciona [21] (Fig. S1).…”