Cloning and expression of melatonin receptors in the mudskipper Boleophthalmus pectinirostris: their role in synchronizing its semilunar spawning rhythm.
The mudskipper Boleophthalmus pectinirostris, a burrow-dwelling fish inhabiting intertidal mudflats, spawns only once during the spawning season around either the first or last lunar quarters. To understand the molecular mechanisms regulating this semilunar spawning rhythm, we cloned all melatonin receptor subtypes (mtnr1a1.4, mtnr1a1.7, mtnr1b, and mtnr1c). Expression of three melatonin receptor subtypes (except mtnr1c) was found in the ovaries. In contrast, the expression of all receptor subtypes was found in the diencephalon and the pituitary. In the fully-grown follicles, only mtnr1a1.7 mRNA was detected in both the isolated follicle layers and denuded oocytes. Interestingly, the transcript levels of both mtnr1a1.4 in the diencephalon and mtnr1a1.7 in the ovary displayed two cycles within one lunar month, and peaked around the first and last lunar quarters. We used 17α,20β-dihydroxy-4-pregnen-3-one (DHP), a maturation-inducing hormone, as a biomarker to examine the involvement of melatonin receptors in the control of the spawning cycle. Melatonin significantly increased the plasma DHP level 1h post intraperitoneal injection. Melatonin also directly stimulated ovarian fragments in vitro to produce a significantly higher amount of DHP. Taken together, these results provided the first evidence that melatonin receptors were involved in the synchronization of the semilunar spawning rhythm in the female mudskipper by acting through the HPG axis and/or directly on ovarian tissues to stimulate the production of DHP.
State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, China; College of Ocean and Earth Sciences, Xiamen University, Xiamen 361005, China.
Lu Yan
LY
Hong
State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, China; College of Ocean and Earth Sciences, Xiamen University, Xiamen 361005, China.
Wan Shu
WS
Hong
College of Ocean and Earth Sciences, Xiamen University, Xiamen 361005, China.
Wen Bo
WB
Zhu
Shenzhen Key Laboratory of Marine Genomics, Marine and Fisheries Institute, BGI, Shenzhen 518083, China.
Qiong
Q
Shi
Shenzhen Key Laboratory of Marine Genomics, Marine and Fisheries Institute, BGI, Shenzhen 518083, China.
Xin Xin
XX
You
State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, China; College of Ocean and Earth Sciences, Xiamen University, Xiamen 361005, China. Electronic address: chenshixi@xmu.edu.cn.
Shi Xi
SX
Chen
D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular / Q000379:methods*; D005260:Female; D008969:Molecular Sequence Data; D016081:Moon; D010053:Ovary / Q000254:growth & development / Q000378:metabolism; D010473:Perciformes / Q000378:metabolism*; D010507:Periodicity; D010802:Phylogeny; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D044094:Receptors, Melatonin / Q000235:genetics / Q000378:metabolism*; D012098:Reproduction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012621:Seasons; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution
D012333:RNA, Messenger; D044094:Receptors, Melatonin
17α,20β-Dihydroxy-4-pregnen-3-one; Boleophthalmus pectinirostris; Diurnal rhythm; Melatonin receptor; Semilunar periodicity