Evolution of calcium homeostasis and its hormonal regulation in vertebrates
Preface: Comparative and general aspects of calcium homeostasis and its hormonal regulations
Edited by Nobuo Suzuki and Tatsuya Sakamoto
Calcium is an essential mineral to maintain cell viability and, ultimately, animal life. In all vertebrates, blood calcium levels are strictly kept at a constant concentration (around 2.5 mM) in spite of changes in the internal milieu or external environment, although the requirements for this mineral and its availability have varied considerably in the course of animal evolution especially when animals have changed their characteristic habitats. Creatures of the sea, which is rich in calcium, excrete extra calcium from the gill and kidney. On the other hand, freshwater fish, which live in a low calcium environment, and terrestrial vertebrates (tetrapods) must obtain calcium from their environments or diets. For this reason, the role of calcemic hormones appears to have changed in each animal, while the general function of each may have remained.
For example, calcitonin is a 32 amino-acid peptide hormone that has a hypocalcemic action by suppressing osteoclasts (bone resorptive cells). However, even cartilaginous fish without osteoclasts also possesses calcitonin (Copp et al., 1967). The roles of calcitonin in cartilaginous fish as well as other primitive and non-mammalian vertebrates were not elucidated for a long time, although the primary structures of calcitonins in some species have been determined. Against this background, the journal Zoological Science and the former journal Zoological Magazine published many studies on the specific/general functions of this hormone through vertebrates, i.e., Agnathans, cartilaginous fish, teleost fish, amphibians, and reptiles. Particularly, the physiological role of calcitonin in the frog was clarified by Oguro et al. (1984), and their study received the first Zoological Science Award. The roles of other calcemic hormones, e.g., staniocalcin, which was believed to be fish-specific but has been identified later in human (Olsen et al., 1996), vitamin D3, the parathyroid hormone, the parathyroid hormone-related protein, and prolactin have also been investigated in articles published in the above two journals. The roles of these hormones in various animals have been reviewed and the general functions of these hormones discussed from the evolutionary point of view also in Zoological Science (Sasayama, 1999).
A significant step forward in our understanding of calcium homeostasis was the development of excellent models of calcified tissues. Using teleost scale, which contains formative cells (osteoblasts) and osteoclasts such as mammalian bone, a new in-vitro system to analyze bone metabolism was established by Takahashi et al. (2008). This scale in vitro system can readily analyze the crucial interaction between osteoblasts and osteoclasts, as evaluated in mammals in vivo (Teitelbaum, 2000). Eventually, a drug to cure human osteoporosis was developed (Suzuki et al., 2008). Furthermore, space experiments with this scale model have been performed in the International Space Station since 2010 to examine bone metabolism under microgravity. Thus, the two journals published by the Zoological Society of Japan have been considered to lead in both basic and applied areas in this field.
From these comparative and general viewpoints, this special issue has succeeded at integrating significant studies on calcium homeostasis in vertebrates in the chapters listed below. Although this issue is limited to vertebrates, similar calcification mechanisms have been discovered in invertebrates (Sudo et al., 1997), and calcitonin and its receptor have also been identified (Sekiguchi et al., 2009). Our hope is that this issue will encourage further investigation of calcium homeostasis and that an increasing number of scientists from basic and applied areas in the world will contribute to this fertile field of calcium homeostasis.
REFERENCES
- Copp DH, Cockcroft DW, Kueh Y (1967) Calcitonin from ultimobranchial glands of dogfish and chickens. Science 158: 924-925
- Oguro C, Fujimori M, Sasayama Y (1984) Changes in the distribution of calcium in the frog, Rana nigromaculata following ultimobranchialectomy and calcitonin administration. Zool Sci 1: 82-88
- Olsen HS, Cepeda MA, Zhang QQ, Rosen CA, Vozzolo BL, Wagner GF (1996) Human stanniocalcin?a possible hormonal regulator of mineral metabolism. Proc Natl Acad Sci USA 93: 1792-1796
- Sasayama Y (1999) Hormonal control of Ca homeostasis in lower vertebrates: Considering the evolution. Zool Sci 16: 857-869
- Sekiguchi T, Suzuki N, Fujiwara N, Aoyama M, Kawada T, Sugase K, Murata Y, Sasayama Y, Ogasawara M, Satake (2009) Calcitonin in a protochordate, Ciona intestinalis: The prototype of the vertebrate Calcitonin/Calcitonin gene related peptide superfamily. FEBS J 276: 4437-4447
- Sudo S, Fujikawa T, Nagakura T, Ohkubo T, Sakaguchi K, Tanaka M, Nakashima K, Takahashi T (1997) Structures of mollusc shell framework proteins. Nature 387: 563-564
- Suzuki N, Somei M, Seki A, Reiter RJ, Hattori A (2008) Novel bromomelatonin derivatives as potentially effective drugs to treat bone diseases. J Pineal Res 45: 229-234
- Takahashi H, Suzuki N, Takagi C, Ikegame M, Yamamoto T, Takahashi A, Moriyama S, Hattori A, Sakamoto T (2008) Prolactin inhibits osteoclastic activity in the goldfish scale: A novel direct action of prolactin in teleosts. Zool Sci 25: 739-745
- Teitelbaum SL (2000) Bone resorption by osteoclasts. Science 289: 1504-1508