Tài liệu Báo cáo khoa học: Osmotic stress sensing and signaling in fishes doc

MINIREVIEW

Osmotic stress sensing and signaling in fishes

Diego F. Fiol and Dietmar Ku¨ ltz

Physiological Genomics Group, Department of Animal Science, University of California, Davis, CA, USA

Physiological significance of osmotic

stress for fishes

Fishes represent the most ancient of five vertebrate

classes. They originated more than 500 million years

ago and have diverged into three major taxa: (a) hag￾fishes and lampreys (Agnatha); (b) cartilagenous fishes

(Chondrichthyii); and (c) ray-finned fishes (Actino￾pterygii). These three taxa employ different strategies

of systemic osmoregulation with only ray-finned fishes

being strong osmoregulators. Nevertheless, at the cellu￾lar level, all fish taxa (like other organisms) ionoregu￾late to maintain K+ and other intracellular inorganic

ion concentrations within a tightly regulated range,

which is essential to support cell metabolism.

Like other aquatic (or semiaquatic) vertebrates (e.g.

amphibians, alligators), fish are in direct contact with

environmental water. Most fishes depend on stable

water salinity to be able to osmoregulate and maintain

constant osmolality in their body fluids (internal

milieu). These are stenohaline species that can only live

in either freshwater or seawater. Nonetheless, there are

also numerous fish species that tolerate and even thrive

in water characterized by greatly fluctuating salinity.

Keywords

euryhaline fishes; osmoregulation;

osmosensing; osmotic stress; salinity

adaptation; stress signaling

Correspondence

D. Ku¨ltz, Comparative Physiological

Genomics Group, Department of Animal

Science, One Shields Avenue, Meyer Hall,

University of California, Davis, CA 95616,

USA

Fax: +1 530 752 0175

Tel: +1 530 752 2991

E-mail: [email protected]

(Received 2 July 2007, accepted

7 September 2007)

doi:10.1111/j.1742-4658.2007.06099.x

In their aqueous habitats, fish are exposed to a wide range of osmotic con￾ditions and differ in their abilities to respond adaptively to these variations

in salinity. Fish species that inhabit environments characterized by signifi￾cant salinity fluctuation (intertidal zone, estuaries, salt lakes, etc.) are eury￾haline and able to adapt to osmotic stress. Adaptive and acclimatory

responses of fish to salinity stress are based on efficient mechanisms of

osmosensing and osmotic stress signaling. Multiple osmosensors, including

calcium sensing receptor likely act in concert to convey information about

osmolality changes to downstream signaling and effector mechanisms. The

osmosensory signal transduction network in fishes is complex and includes

calcium, mitogen-activated protein kinase, 14-3-3 and macromolecular

damage activated signaling pathways. This network controls, among other

targets, osmosensitive transcription factors such as tonicity response ele￾ment binding protein and osmotic stress transcription factor 1, which, in

turn, regulate the expression of genes involved in osmotic stress acclima￾tion. In addition to intracellular signaling mechanisms, the systemic

response to osmotic stress in euryhaline fish is coordinated via hormone￾and paracrine factor-mediated extracellular signaling. Overall, current

insight into osmosensing and osmotic stress-induced signal transduction in

fishes is limited. However, euryhaline fish species represent excellent models

for answering critical emerging questions in this field and for elucidating

the underlying molecular mechanisms of osmosensory signal transduction.

Abbreviations

CaSR, calcium sensing receptor; IEG, immediate early gene; MAPK, mitogen-activated protein kinase; Ostf1, osmotic stress transcription

factor 1; TonEBP, tonicity response element binding protein; TRP, transient receptor potential.

5790 FEBS Journal 274 (2007) 5790–5798 ª 2007 The Authors Journal compilation ª 2007 FEBS