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Munetaka Shimizu, Ph.D.
Professor
Field Science Center for Northern Biosphere
Hokkaido University (HU)
(Graduate School/School of Fisheries Sciences, HU)
3-1-1 Minato, Hakodate, Hokkaido 041-8611, Japan
Office: +81-138-40-8897
e-mail: mune◎fish.hokudai.ac.jp
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Employment & Eduction
2021- : Professor
Field Science Center for Northern Biosphere, HU
2016 -2021: Associate Professor
Faculty of Fisheries Sciences, HU
2006-2016: Lecturer
Faculty of Fisheries Sciences, HU
1999-2005: Research Associate
School of Aquatic and Fishery Sciences
University of Washington (UW)
& Northwest Fisheries Science Center
NOAA Fisheries
1997-1999: JSPS Research Fellow
HU and UW
1997: Ph.D. in Fisheries, HU, Japan
Research at the Shimizu Lab
Research areas of Dr. Mune Shimizu are fish physiology and comparative endocrinology which are related to Aquaculture and Resource Enhancement. The research at the Shimizu Lab focuses on the mechanisms of endocrine regulation of growth in salmonids and its modulation by environments. The Shimizu Lab is also interested in understanding how growth opportunities and environments influence the life-history patterns of salmonids.
The research approaches of the Shimizu Lab are based on the current understanding in the somatotropic axis. The growth of animal is primarily regulated by growth hormone and insulin-like growth factor-I. Growth hormone (GH) from the pituitary gland stimulates hepatic production of insulin-like growth factor (IGF)-I. IGF-I from the liver circulates in the blood and mediates many of growth promoting actions of GH. Endocrine IGF-I forms a negative feedback loop to the pituitary gland through inhibiting GH synthesis and release. IGF-I is also synthesized in peripheral tissues and acts as a local growth factor, which is indeed essential for normal postnatal growth. Circulating IGF-I is tightly associated with multiple IGF-binding proteins (IGFBPs). Because the affinity to IGF-I of IGFBPs is higher than that of the receptor, IGFBPs are capable of controlling availability of IGF-I to target tissues. Dr. Shimizu's lab especially focuses on IGF-I and IGFBPs to understand how growth of salmon is regulated by these hormone/proteins. Better understanding of growth regulation and developing growth/stress indices should promote aquaculture, resource enhancement, stock management and conservation for salmon. The major projects in this lab are listed below.
Current projects
1. Mechanism of endocrine regulation of growth in salmon
2. Hormone/proteins as growth/stress indices
3. Environmental modulation of smoltification
1. Mechanism of endocrine regulation of growth in salmon
In mammals, there are six types of IGFBPs 1-6 that either inhibit or promote IGF-I activity. Teleosts underwent an extra round of whole genome duplication and thus could have two co-orthologs of each member of the IGFBP family, except IGFBP-4.
In salmon circulation, three major IGFBP bands are detected at 41, 28 and 22 kDa. The Dr. Shimizu Lab identified these forms, through protein purification, N-terminal amino acid analysis and cDNA cloning, as IGFBP-2b, -1a and -1b. Our lab is now trying to produce recombinant proteins of these IGFBPs for functional analyses. It is now clear that salmonids have 22 IGFBP repertories due to an autotetraploidization event. For instance there are four paralogs of IGFBP-1 (1a1, 1a2, 1b1 and 1b2). Based on this fact, recombinant proteins for these subtypes are being produced.
2. Hormones/proteins as growth/stress indices
The Shimizu Lab has validated and developed immunoassays for IGF-I and IGFBPs. A series of rearing experiments revealed that circulating IGF-I and IGFBP-2b were generally positively correlated with individual growth rate in salmon, whereas negative relations were found between circulating IGFBP-1s and growth under stressful conditions. The Shimizu Lab utilizes these endocrine parameters as quantitative indices of growth and stress.
An example of utilizing IGF-I and IGFBPs as endocrine tools is the evaluation of growth status in out-migrating juvenile chum salmon. Most salmonids are believed to suffer growth-dependent mortality during the early phase of their marine lives. In order for juvenile salmon to survive during this period, they should attain a certain size at a certain time. Thus, monitoring growth rate of out-migration juveniles is of great importance to evaluate the risk of growth-dependent mortality thereafter. The Shimizu Lab utilizes IGF-I and IGFBP-1b as positive and inverse growth indices, respectively, to evaluate the growth status of juvenile chum salmon on the Abashiri coast, northeastern Hokkaido, Japan.
3. Environmental modulation of smoltification
Masu salmon (Oncorhynchus masou) is one of eight Pacific salmon species distributed only on the Asian side of the Pacific Ocean. This species comprises three subspecies: masu salmon (O. masou masou), amago salmon (O. masou ishikawae), and Biwa salmon (O. masou subsp.), which differ in their distribution, life history patterns and hypo-osmoregulatory capability. Masu and amago salmon are anadromous, migrating downstream to the ocean in the second spring and first fall in their lives, respectively. The Biwa salmon subspecies has been land-locked in the Lake Biwa watershed for approximately 500,000 years and thus has reduced considerably its ability to adapt to saltwater. The research at the Shimizu Lab mainly targets to the O. masou species complex as a model to unravel the mechanisms of growth, hypo-osmoregulation, and their interaction because it has been a target of hatchery release, aquaculture and conservation.
The current project in the lab is to examine effects of photoperiod on the timing and degree of smoltification and early maturation in masu salmon from Hokkaido, Japan. A square-wave photoperiod during early summer has been proven to be effective to induce off-season smolts in masu salmon. However, the response to the photoperiod manipulation differs among strains. The Shimizu Lab is interested in disentangling environment and genetic interactions to understand the mechanism of the decision making for smoltification using the photoperiod manipulation and different strains.
