Novel Discoveries in Acid-base Regulation and Osmoregulation: New Actions of Old Hormones
Jia-Jiun Yan and Pung-Pung Hwang*
Institute of Cellular and Organismic Biology, Academia Sinica, Taipei, Taiwan
Maintaining internal ionic and pH homeostasis is critical for survival in all biological systems. Aquatic fish, similar to mammals, developed sophisticated mechanisms to transport various ions or acid equivalents under hormonal control for body fluid homeostasis when systemic ionic and acid-base status is disturbed by metabolic or environmental stresses. The mechanisms are particularly challenging to fish because aquatic environments are diverse in ion composition and pH level. To overcome the research limitations in traditional model species, zebrafish has been recently used as an emerging model to study the molecular physiology of ionic and acid-base regulation mechanisms and the actions of hormones in fish. Some of them have been identified to show novel actions that were unknown in vertebrates. Oxytocin was known to reduce blood pressure through stimulating atrial natriuretic peptide. The fish homologous, isotocin, was identified to stimulate the proliferation of epidermal stem cells and differentiation of ionocyte progenitors, consequently enhancing uptake of various ions. Stanniocalcin-1, a well-documented hypocalcemic hormone, was identified as a negative regulator for ionocyte differentiation and thus suppressing acid secretion and the uptake of Na+ and Cl-. On the other hand, estrogen-related receptor a is an orphan nuclear receptor for adaptive metabolic responses under stresses and reveals a novel action to stimulate acid secretion by regulating the differentiation of H+-ATPase expressing ionocytes. Furthermore, we recently explored that calcitonin gene-related peptide (CGRP) is a hypochloremic hormone, unlike its splice variant calcitonin, which is a hypocalcemic hormone. CGRP exerts suppressive action on Cl- uptake through down-regulating the density of Na+-Cl--cotransporter-expressing ionocytes. As such, the knowledge obtained in zebrafish not only enhances our understanding of the hormonal control of fish acid-base and osmotic regulation but also informs studies on other animal species, thereby providing insights into related fields.
Key Words: Zebrafish, acid-base regulation, ion uptake, transporters, ionocytes, isotocin, stanniocalcin, estrogen-related receptor, calcitonin gene-related peptide
Jia-Jiun Yan and Pung-Pung Hwang*
Institute of Cellular and Organismic Biology, Academia Sinica, Taipei, Taiwan
Maintaining internal ionic and pH homeostasis is critical for survival in all biological systems. Aquatic fish, similar to mammals, developed sophisticated mechanisms to transport various ions or acid equivalents under hormonal control for body fluid homeostasis when systemic ionic and acid-base status is disturbed by metabolic or environmental stresses. The mechanisms are particularly challenging to fish because aquatic environments are diverse in ion composition and pH level. To overcome the research limitations in traditional model species, zebrafish has been recently used as an emerging model to study the molecular physiology of ionic and acid-base regulation mechanisms and the actions of hormones in fish. Some of them have been identified to show novel actions that were unknown in vertebrates. Oxytocin was known to reduce blood pressure through stimulating atrial natriuretic peptide. The fish homologous, isotocin, was identified to stimulate the proliferation of epidermal stem cells and differentiation of ionocyte progenitors, consequently enhancing uptake of various ions. Stanniocalcin-1, a well-documented hypocalcemic hormone, was identified as a negative regulator for ionocyte differentiation and thus suppressing acid secretion and the uptake of Na+ and Cl-. On the other hand, estrogen-related receptor a is an orphan nuclear receptor for adaptive metabolic responses under stresses and reveals a novel action to stimulate acid secretion by regulating the differentiation of H+-ATPase expressing ionocytes. Furthermore, we recently explored that calcitonin gene-related peptide (CGRP) is a hypochloremic hormone, unlike its splice variant calcitonin, which is a hypocalcemic hormone. CGRP exerts suppressive action on Cl- uptake through down-regulating the density of Na+-Cl--cotransporter-expressing ionocytes. As such, the knowledge obtained in zebrafish not only enhances our understanding of the hormonal control of fish acid-base and osmotic regulation but also informs studies on other animal species, thereby providing insights into related fields.
Key Words: Zebrafish, acid-base regulation, ion uptake, transporters, ionocytes, isotocin, stanniocalcin, estrogen-related receptor, calcitonin gene-related peptide