Chaetognaths: a useful model for studying heat shock proteins. Effect of wound healing

312 (2004) 319–332

www.elsevier.com/locate/jembe

Chaetognaths: a useful model for studying heat

shock proteins. Effect of wound healing

S. Jean, L. De Jong, X. Moreau*

Laboratoire de Biologie Animale (Plancton), ER bBiodiversite et Environnement Q, case 18,

Universite de Provence, 13331 Marseille Cedex3, France

Received 23 February 2004; received in revised form 27 June 2004; accepted 20 July 2004

Abstract

The pattern of expression of Heat Shock Protein 70 (Hsp70), a highly conserved cellular protein

chaperone, was investigated in Chaetognatha, a very important phylum of marine worms, which play

a major role in marine food webs. The in toto distribution of Hsp70-like immunoreactivity was

assessed in both intact and experimentally wounded specimens of Spadella cephaloptera Busch,

1851 that have been cut transversally just above the seminal vesicles. In intact animals, the ciliary

organs, the corona ciliata, the coronal nerve and the spermatocytes express Hsp70 proteins. The

kinetic of the expression pattern has been followed during the wound healing from the lesion to 5

days after. The Hsp70 immunoreactivity was observed according to time in the cerebral and

suboesophageal ganglia and in the plexuses of the hood, the mouth, the neck and the tail region. At

the wound level, the time-dependent Hsp70 expression was detected in the epidermal cells and along

numerous muscle fibres of the tail region. Five days after the tail section, two Hsp70 immunoreactive

areas were observed on both sides of the healed wound that correspond to the sites of formation of

two new seminal vesicles. It is suggested that, in Chaetognaths, Hsp70 may be implicated in the

regulation of several cellular processes especially at the level of the spermatocytes in intact and

wounded specimens, and of the nervous system and muscular apparatus during the wound healing. It

appears that chaetognaths are a good model as indicator of stress responses for experimental studies

at the level of a whole organism.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Chaetognaths; Heat shock proteins; Spadella cephaloptera; Wound

* Corresponding author. Fax: +33 4 91 10 62 65.

0022-0981/$ -

doi:10.1016/j.

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Journal of Experimental Marine Biology and Ecology

see front matter D 2004 Elsevier B.V. All rights reserved.

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ress: [email protected] (X. Moreau).

S. Jean et al. / J. Exp. Mar. Biol. Ecol. 312 (2004) 319–332320

1. Introduction

Chaetognaths, also called arrow worms, are marine organisms that constitute a small

phylum of very abundant animals. They play an important role in marine food webs

(Feigenbaum, 1991) and most of them are planktonic.

For many experimental studies, the chaetognath appears as a model animal for the

following reasons. Indeed, this taxon includes small species; their body is transparent

allowing in toto observations especially convenient for immunolabeling. They have a

simple body plane and lack digestive glands, circulatory apparatus, respiratory and

excretory organs (Duvert et al., 2000 for review). Lastly, benthic species such as Spadella

cephaloptera Busch, 1851 are easily kept alive in laboratory conditions. In natural

environments, living specimens lacking part of their body or showing obvious scars are

not infrequent in some regions of the world (Burfield, 1927; Pierce, 1951; Duvert et al.,

2000).

A previous experimental work (Duvert et al., 2000) was conducted to study the

histological and cytological aspects of wound healing in Chaetognatha. This model

organism appears to be particularly resistant in such experiments. The authors have

shown that specimens could survive for at least 30 days after a decapitation and that, in

such conditions, they are still able to mate. Moreover, after their amputation, the

seminal vesicles are formed in about a week. In fact, chaetognaths lacking head or tail

are able to restore the organization of their bodies by re-establishing their body

cavities. For these reasons, the chaetognath S. cephaloptera has been retained to

investigate some processes involved in the cicatrisation and regeneration of tissues

during wound healing. The cutting of a part of the animal generates an immediate

stress for the organism and the injured tissues. This stressful experiment is postulated

to influence the expression of a category of very important proteins, the heat shock

proteins (Hsp).

Hsp are a family of highly conserved cellular protein chaperones identified in a wide

range of organisms from microorganisms to humans. Constitutively expressed, they play

an important role in fundamental cellular processes such as folding, secretion and

degradation of other proteins (Mayer and Bukau, 1998). They act through cycles of

substrate binding and release governed by ATP binding and hydrolysis (Bukau and

Horwich, 1998; Hartl and Hayer-Hartl, 2002). Most of these proteins, especially the Hsp70

subfamily, are stress-inducible and accumulate in cells upon exposures to various kinds of

chemical and physical stressors. Increased expression of Hsp70 has been shown to be

protective in many cultured cells and animals tissues (Kiang and Tsokos, 1998; Nollen et

al., 1999; Kalmar et al., 2002). This protection is mediated by the capacity of Hsp70 to

prevent inappropriate protein aggregation, to facilitate the restoration of the function of the

renaturated proteins, and to mediate transport of irreversible damaged proteins to

degradative organelles and proteasomes. Thus, Hsp70 proteins allow cells to adapt to

abrupt or gradual changes of their environment and to survive in some cases to lethal

conditions.

The purpose of the present study is to describe the pattern of expression of Hsp70 in the

chaetognath S. cephaloptera, and to assess the effect of wound healing on its expression.

For a better understanding of the location of the regions and body structures that express

Fig. 1. General organization of the body and main features of the head nervous system in S. cephaloptera. (A)

Light micrograph of a whole specimen. (B) Schematic representation of the head dorsal nervous system. (C)

Schematic representation of the main ventral nervous structures. cc, corona ciliata; cg, cerebral ganglion; cn,

coronal nerve; e, eye; fc, frontal connective; h, hook, hp, hood plexus; lf, lateral fin; ls, longitudinal septum; m,

mouth; mc, main connective; mp, mouth plexus; n, cerebral neuropile; np, neck plexus; on, optic nerve; sog,

suboesophageal ganglion; sv, seminal vesicle; tf, tail fin; ts, transverse septum; vsg, vestibular ganglion.

S. Jean et al. / J. Exp. Mar. Biol. Ecol. 312 (2004) 319–332 321

Hsp70, the main body regions and head nervous system, already described (Bone and

Goto, 1991; Goto et al., 1992; Duvert et al., 1997), are represented in Fig. 1.

2. Material and methods

2.1. Experimental design

The specimens of S. cephaloptera were caught during spring and summer 2003 in a

marine meadows east of Marseille (Brusc lagoon, France). In the laboratory, they were

kept in a 60-l aquarium filled with circulating and continuously aerated natural seawater at

21F1 8C where they were maintained under natural light cycle.

After a week period of acclimation, a randomized set of mature specimens were

captured. Transversal cut was done at the posterior end of tail just above the seminal

vesicles. The animals were then replaced for various periods in the aquarium, imprisoned

in small traps permeable to the aquarium seawater. Five controls and five injured

specimens for each time were then fixed in 0.1 M saline phosphate buffer (PBS, pH 7.2)

containing 4% paraformaldehyde (PFA), immediately or 15, 30 min, 1, 2, 12, 16, 24 h, 2, 3

and 5 days after the cutting. They were stored in PBS–PFA solution at 4 8C until assay.


2.2. Immunohistochemistry

Specimens were rinsed in PBS containing 1% Triton X-100 during 2 days. To saturate

nonspecific sites, entire animals were then pre-incubated for 35 min at room temperature

in 0.1 M PBS containing 1% Triton X-100, 10% goat serum and 2% bovine serum

albumin (PBS-T buffer). Animals were incubated overnight at 4 8C in a dilution (1:2000)

of a primary antibody against Hsp70 raised in mouse (Sigma, Saint Quentin-Fallavier,

France) in PBS-T buffer. This antibody reacts against both the constitutive and the

inducible form of Hsp70. Specimens were then rinsed three times and were incubated for

an hour, in the dark and at room temperature, with a secondary antibody (1:200), goat anti-

mouse IgG TRITC-conjugated (Sigma) diluted in PBS-T buffer. After rinsing in PBS for

2–3 h at room temperature, animals were mounted in a medium containing antifading

(Gel/MountR, Bibmeda, Foster City, CA, USA). Preparations were observed under a

fluorescence microscope (Leica M1560).

3. Results

3.1. Intact specimens

Fig. 2A shows the pattern of expression of Hsp70-like proteins in intact adult

specimens. A positive reaction is observed at the level of the corona ciliata and along the

coronal nerve (Fig. 2B). In the cerebral ganglion, a strong spot-like labeling is present near

the origin of the coronal nerves (Fig. 2C). Aweak labeled network in the epidermis is also

observed and it intensifies near by the corona ciliata (Fig. 2D) and ciliary organs (Fig. 2E),

these latter being distributed all along the body from the head to the tip of the tail (Fig.

2A). Sensory fibres that connect the ciliary organs are Hsp70-like immunoreactive (Fig.

2F). In the tail region, behind the transverse septum, and on both side of the longitudinal

septum, spermatocytes exhibit Hsp70 labeling (Fig. 2G,H). Content of the seminal vesicles

are not immunoreactive (Fig. 2I,J).

3.2. Wounded specimens

During wound healing, the immunoreactive structures observed on intact specimens are

still labeled. However, other labeled structures appear in some parts of the cerebral

nervous system and at the level of the wound. The following results show the

modifications of the expression pattern of Hsp70 in these body regions according to

time after tail section.

3.2.1. Expression pattern of Hsp70 in the cerebral nervous system

The first labeling appears in the cerebral ganglion 15 min after injury (Fig. 3A). It spreads

in the cerebral neuropile (Fig. 3B) and is observed until 30 min. At 30 min, the labeling is

concentrated in two symmetrical areas that correspond to cell bodies in the posterior part of

the cerebral ganglion (Fig. 3C). At the same time, the hood and the mouth plexuses are

immunoreactive (Fig. 3D,E). Two hours after injury, the cell bodies are no more reactive

Fig. 2. Expression pattern of Hsp70 in adult intact specimens of S. cephaloptera. (A) Whole intact specimen

showing constitutive Hsp70 immunoreactivity. Note a positive reaction at the level of the corona ciliata (cc) and

ciliary organs (arrowheads) that are displayed along the whole body from the head to the tail. (B) General view of

the Hsp70 immunoreactive corona ciliata and coronal nerves (cn). (C) Detail of the coronal nerves corresponding

to the area boxed in (B). Note a strong spot-like labeling in the cerebral ganglion at the origin of the coronal

nerves. (D) Enlargement of the corona ciliata. (E) Enlargement of a ciliary organ. Note the Hsp70 immunoreactive

network surrounding the ciliary fence. (F) Lateral view of a ciliary organ. Note sensory Hsp70 immunoreactive

fibres that connect the ciliary organ. (G) Detail of the tail region showing Hsp70 immunoreactive spermatocytes

on both side of the longitudinal septum (ls). (H) Detail of immunoreactive spermatocytes. (I) Enlargement of a

seminal vesicle. The spermatozoa inside the seminal vesicle are not labeled (arrow). (J) Light micrograph of the

same seminal vesicle as in (I), showing the presence of the spermatozoa (arrow). e, eye; sv, seminal vesicle.


while it is still the case for the both abovementioned plexuses. This labeling remains

unchanged until 16 h after amputation. At that time, a strong positive reaction appears in the

neck plexus and in the subKsophageal ganglion (Fig. 3F). This latter does not persist 24 h

2525

Fig. 3. Expression pattern of Hsp70 in the head nervous system in wounded specimens of S. cephaloptera cut

transversally above the seminal vesicles. (A, B) Labeling in the cerebral ganglion 15 min after injury. Labeling is

spread in the cerebral neuropile as detailed in (B). (C, D, E) Labeled structures one hour after injury. (C) Two

Hsp70 immunoreactive cell bodies in the posterior part of the cerebral ganglion. The white asterisk indicates the

location of the right eye. (D) Right hood plexus. (h) Hook. (E) Mouth plexus (arrowheads). (F, G) Labeled

structures 16 h after injury. (F) Strong labeling at the suboesophageal ganglion (arrow). Note that the hood

plexuses are still immunoreactive (arrowheads). (G) Neck plexus.


after the wound, as for the mouth and the hood plexus. However, the neck plexus remains

intensively labeled 2 days after the cutting (Fig. 3G). The intensity of the Hsp70-like

immunoreactive neck plexus decreases progressively and disappears after 3 days.

3.2.2. Expression pattern of Hsp70 at the wound level

Immediately after the transverse cut of the tail, Hsp70 is expressed just alongside the

wound. First, an intense spot-like immunoreactivity is located on one half edge of the


wound (Fig. 4A). Fifteen minutes after, this spot-like labeling spreads on the width of

the cut. It also appears anteriorly in muscle fibres that become Hsp70 immunoreactive

nearby the cut (Fig. 4B,C). During the first 12 h, the labeling progress all along the

numerous muscle fibres of the tail region (Fig. 4D,E). At 12 h, neurons of the tail plexus

Fig. 4. Expression pattern of Hsp70 at the wound level in S. cephaloptera cut transversally just above the seminal

vesicles. (A) Immunoreactive spots on a part of the edge of the wound immediately after injury. (B, C) Fifteen

minutes after injury. (B) The immunoreactive spots observed immediately after injury are now spread on the

width of the cut. Weak labeled muscle fibre (arrow). (C) Detail of the boxed area in (B). (D, E) Immunostaining of

many longitudinal muscle fibres in the tail region 12 h after injury. (E) Enlargement of (D). Labeled muscle fibres

(arrows) and tail plexus (arrowheads). Note the presence of an immunoreactive ciliary organ (co). (F) Sixteen

hours after injury. The labeling is restricted to the wound level. Muscle fibres are immunoreactive (arrows) on a

length that is about twice shorter than in (D). (G) Enlargement of immunoreactive striated muscle fibres showing

the regular expression pattern of Hsp70 (arrows). (H) Three days after injury. Expression of Hsp70 in the tail

plexus. The outline of the wound is now regular and less immunoreactive. (I) Five days after injury. Expression of

Hsp70 in two oval areas on both side of the healed wound. The wound itself is no longer immunoreactive. (J)

Light micrograph corresponding to (I) micrograph. Note that the two immunolabeled areas observed in (I) do not

correspond with a special structure in (J).


express Hsp70 (Fig. 4E). After 16 h, the labeling of the muscle fibres is restricted to the

wound level and is no more visible anteriorly in the tail region (Fig. 4F). In the wound

area, the expression pattern of Hsp70 in striated muscle fibres displays a scale-like

aspect (Fig. 4G). It becomes weaker from 1 to 5 days after the tail section (Fig. 4H),

which allows to set off the Hsp70 immunoreactive tail plexus. During this period, the

outlines of the wound, which had a rough aspect, become regular and smooth. Five days

after the operation, two strong Hsp70-like immunoreactive areas are localized on both

side of the healed wound (Fig. 4I). This unusual labeling does not seem to correspond

with a peculiar structure when animals are observed under transmitted light microscope

(Fig. 4J).

4. Discussion

Only a few studies on multicellular eukaryotes have reported the expression pattern of

Hsp proteins in intact tissues and organisms (Feder and Hofmann, 1999 for review).

Moreover, most of works dealing with Hsp70 expression have been performed under

thermal stress conditions (Feder and Hofmann, 1999 for review). For the first time, the

constitutive expression of Hsp70 proteins in non-stressed and entire animals is described

here using a new animal model, a chaetognath. Furthermore, owing to the remarkable

healing capacity of the chaetognath S. cephaloptera (Duvert et al., 2000), the expression

pattern of Hsp70 following a lesion is observed in the present study.

4.1. Distribution of Hsp70 in control animals

4.1.1. Nervous system and sensitive organs

The immunohistochemical investigations reveal the presence of Hsp70 in sensitive

organs consisting of fans of elongated cilia arranged all along the body. The ciliated

cells constitute sensory cells that receive synapses at their bases (Welsh and Storch,

1983). Cilia and sensory cells are involved in the response to short range vibrations,

chiefly to deformation by water movements in the transverse plane to the axis of the

organ. Hsp70 is also expressed in the corona ciliata. In S. cephaloptera, this organ is

elliptical and lies across the neck where an inner ring of secretory cells is surrounded by

a single ring of ciliated cells. The function of the ciliary loop remains enigmatic.

Malakhov and Frid (1984) have first described this organ at the ultrastructural level and

have shown the presence of primary receptor cells with branching cilia. To a certain

extent, as the corona ciliata is linked to the coronal nerve, which is itself connected to

the cerebral ganglion, this former may have sensitive functions. Indeed, increasing body

of evidence shows that cilia also play prominent roles as sensory organelles (Sloboda,

2002). However, on the basis of the present results, it is difficult to hypothesize the

Hsp70 function in the ciliary organs of chaetognaths. Cilia and flagella are dynamic cell

structures presenting a continuous transport of axonemal particles between them and the

cytoplasm. It has been shown that, in green microalgae, in protozoa and in sea urchin

embryos, several Hsp70 family members are associated with microtubule nucleation,

tubulin transport and/or axoneme assembly (Bloch and Johnson, 1995; Williams and


Nelsen, 1997; Stephens, 1997). Therefore, these molecular chaperones, also involved in

protein turnover, play an important role in the structure and the biogenesis of cilia

(Stephens and Lemieux, 1999). In chaetognaths, the intense Hsp70-like immunoreac-

tivity of the ciliary organs and the corona ciliata may be explained by at least two non-

exclusive hypotheses. First, the cilia of these two structures that are exposed to the

external environment might be frequently damaged and so, it can be assumed that an

intense protein turnover occurs. A second hypothesis could be linked to the presence of

nervous terminals in the ciliary organs and in the corona ciliata. Hsp70 immunoreactivity

in the coronal nerve strengthens this hypothesis. Indeed, the constitutive form of Hsp70

plays a critical role in the regulation of the neurotransmitter release at the level of the

synaptic contacts (Zinsmaier and Bronk, 2001). This process leads to repeated cycles of

exocytosis and endocytosis. It also requires that the participating components are rapidly

recycled and that they sustain an optimal conformation despite repeated use. Hsp70

proteins are involved in the process of exocytosis (Zinsmaier et al., 1994;

Mastrogiacomo et al., 1994; Bronk et al., 2001) and take part in the synaptic vesicle

recycling (Morgan et al., 2001).

4.1.2. Testes

Hsp70 proteins were also observed in circulating spermatocytes in the general cavity

of the tail region. In these animals, the spermatogenesis occurs according to a special

mode. Indeed, the testes lie in the tail cavities close to the transverse septum. Clusters of

spermatogonia continuously depart from the testes and continue their maturation while

floating in the liquid which fills the cKlomic cavities; different stages of spermato-

genesis co-exist in these tail cavities but immature spermatocytes predominate. They are

in constant motion in each tail cavity, owing to the ciliated cells that cover the median

septum (Ghirardelli, 1968). The Hsp70 protein was found to be essential for

spermatogenic cell development especially during the meiotic phase of spermatogenesis

as male mice defective for the hsp70 gene are infertile (Eddy, 1999). Indeed, Hsp70 is

required for the assembly of the maturation promoting factor which is needed for the

G2-M transition in the primary spermatocytes. In this review, it was also specified that

homologues of Hsp70 are present in the testes of mammals, birds, amphibians and

fishes, suggesting that the role of this spermatogenic cell chaperone is conserved across

phyla. In Drosophila, it seems that other molecular chaperones (Hsp23, Hsp27, Hsp60

and Hsp90) are involved in the spermatogenesis process (Michaud et al., 1997; Yue et

al., 1999; Timakov and Zhang, 2001). In this invertebrate, the synthesis of Hsp70 in

testes is observed only under heat shock conditions (Michaud et al., 1997).

Alternatively, the finding of Hsp70-like proteins in the chaetognath spermatocytes

supports the necessity of this protein during the spermatogenesis as described for

vertebrates (Eddy, 1999).

4.2. Wounded specimens

4.2.1. The cerebral nervous system

Immediately after the tail section and during the wound healing process, the expression

pattern of Hsp70 was modified, not only at wound level but also in the cerebral nervous


system. In the cerebral nervous system, the expression of Hsp70 was early and transiently

observed in the neuropile and later in some cell bodies of the cerebral ganglion. Therefore,

it can be assumed that the cerebral ganglion is involved in the regulation of the response to

the injury. This phenomenon may reveal an intensification of the neuronal activity, on the

one hand at the level of the synapses in the neuropile and, on the other hand, by an

activation of cell signaling pathways in which the formation of protein complexes and

their regulation are Hsp70-dependent. The hood, the mouth and the neck plexuses were

also immunoreactive according to time from half an hour to 3 days after the injury. These

plexus networks present numerous varicosities where Hsp70 may be over expressed in

wounded animals. However, the reasons why these plexuses, which innerve the mouth and

other head elements, are immunoreactive remain enigmatic in the wounded animals. In this

context, the labeling of the tail plexus that is frequently observed in this experiment is

more comprehensive because the plexus is partly damaged by the tail section, and so,

Hsp70 are needed to avoid protein breakdown and allow the folding of newly synthesized

proteins.

4.2.2. The tail region

Chaetognaths are built around a large hydroskeleton that is limited by a strong

connective tissue, the basement membrane, which is covered outside by a stratified

epidermis. On the internal face of the basement membrane, four large longitudinal muscle

quadrants in the trunk and in the tail maintain the body architecture and allow

locomotion. In the tail region, the transverse section of the tail affects the body

organization of chaetognaths. Immediately after the cut, a spot-like Hsp70 immunor-

eactivity was observed at the edges of the wound. The superficial localization of this

immunostaining suggests that the induction of Hsp70 occurs in epidermal cells where

these proteins play their role of molecular chaperones and mediate the cellular protection.

The wound opens the body cavity to the external environment, so animals must face

rapidly to preserve their binternal milieuQ and to survive. The sequential wound healing of

beheaded S. cephaloptera has been analyzed at the histological and the ultrastructural

levels (Duvert et al., 2000). This study has shown that, first the muscles contract rapidly

to physically close the wound and isolate the general cavity from the seawater. Then, the

muscular layer of the body wall is reshaped to close up the wound whilst a bclotQ, ahypothesized gel-like substance, is produced to increase the mechanical resistance of the

body wall. In the present study, an Hsp70-immunoreactivity in circulating spermatocytes

is observed as early as 30 min after the section of the tail region (data not shown)

indicating that the wound closure has occurred subsequently to muscular contraction.

Besides, a large and unlabeled area is also frequently visible on both side of the

longitudinal caudal septum slightly anteriorly to the wound (Fig. 4H). This dark region

may correspond to the bclotQ situated in the aqueous phase of the general cavity. This plug

does not exhibit a cellular/tissular organisation as demonstrated by Duvert et al. (2000).

Therefore, the cytosolic Hsp70 protein is not expressed in the body regions where the

bclotQ is present.The fibres of the muscular apparatus are strongly Hsp70 immunoreactive during 24 h

in wounded animals as compared with intact specimens where this typical labeling has

never been observed. This early and remarkable induction of Hsp70 expression in the


contractile apparatus may be achieved by a wide range of elaborate regulatory strategies

at both transcriptional and post-transcriptional levels as described in Drosophila

melanogaster and mammals (Huang et al., 2001; Kaarniranta et al., 1998). The

production of Hsp70 in skeletal muscles of mammals has been observed during and after

a high contractile activity (Neufer et al., 1998). The Hsp70 proteins are supposed to

influence the excitation–contraction coupling process, either directly or indirectly in

these muscles (Nosek et al., 2000). However, little is known about the relationships

between the level of expressed Hsp70 within skeletal muscles and their functions, in

particular concerning their response to the occurrence of the damaged myofibres and to

an acute contraction. High-intensity muscular contraction has been shown to produce

oxidative stress and to generate damaged proteins (Essig and Nosek, 1997). Therefore,

the increase of Hsp70 synthesis may prevent these detrimental effects of fatiguing

stimulation and may enhance an adaptation to stress (Liu et al., 2004; McArdle et al.,

2004). Finally, these proteins have also been detected during skeletal muscle

regeneration suggesting an additional function in the remodeling response of muscle

tissue (Duguez et al., 2003). Thus, in chaetognaths, it can be assumed that the presence

of Hsp70 in muscle fibres a few minutes after the tail section until 24 h may result from

the multiple processes mentioned above in relation with their contraction and

regeneration.

Five days after amputation, as the wound healing was fulfilled, two labeled areas

were visible on the lateral posterior edge of the scar in one of the specimens. The

location and shape of the labeled areas, and the delay after which the Hsp70 appears are

in agreement with the results of Duvert et al. (2000). These authors have described the

formation of the seminal vesicles in the place of the observed immunoreactive areas a

week after the tail cutting. These structures were not detected in the present study when

the chaetognaths were observed under a transmitted light microscope. Therefore, it can

be assumed that Hsp70 expression precedes the formation and the maturation of the

seminal vesicles of the injured specimen cut off above the vesicles. Although the

biological mechanism is unknown, Hsp70 may be involved in the regulation of these

phenomena.

It can be concluded that the multiple functions of the constitutive form of Hsp70,

already described in diverse organisms, are illustrated here in the Chaetognatha. These

functions imply several specific co-chaperones, also highly conserved, that participate

in vesicle secretion and recycling, protein transport, and in the regulation of the

assembly and/or disassembly of protein complexes as reviewed by Young et al.

(2003). Besides, the present study demonstrates that the considerable power of healing

of Chaetognatha requires both the constitutive and inducible forms of Hsp70. These

chaperone proteins contribute, at least in part, to restore the body wall allowing the

survival of the wounded animal. Moreover, they are involved in the sperm maturation

and in the seminal vesicle formation, i.e. two major steps of the reproductive process

of the species. The chaetognaths have already been recognized as a model animal in

phylogeny (Casanova et al., 2001), owing to both molecular data that place them at

the root of the triploblastic radiation (Telford and Holland, 1993, 1997; Papillon et

al., 2003) and their simple body plan permitting the easy observation of gene markers

(Yasuda et al., 1997; Takada et al., 2002). The present study shows that the


chaetognath could also be, when associated with Hsp70 expression, a good model

as an indicator of abiotic and biotic stress responses at the level of the whole

organism.

Acknowledgements

The authors are indebted to Dr. J.-P. Casanova, who introduced us to the biology of

chaetognaths, and to whom this article is dedicated. We thank him for his valuable

comments and his critical suggestions for the manuscript. [SS]

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Documents

Chaetognaths: a useful model for studying heat shock proteins. Effect of wound healing