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Diurnal and Circadian Oscillations in Expression of Kisspeptin, Kisspeptin Receptor and Gonadotrophin‐Releasing Hormone 2 Genes in the Grass Puffer, A Semilunar‐Synchronised Spawner
Author(s) -
Ando H.,
Ogawa S.,
Shahjahan Md.,
Ikegami T.,
Doi H.,
Hattori A.,
Parhar I.
Publication year - 2014
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1111/jne.12165
Subject(s) - kisspeptin , endocrinology , medicine , circadian rhythm , biology , clock , preoptic area , gonadotropin releasing hormone , hypothalamus , circadian clock , hormone , luteinizing hormone
In seasonally breeding animals, the circadian and photoperiodic regulation of neuroendocrine system is important for precisely‐timed reproduction. Kisspeptin, encoded by the K iss1 gene, acts as a principal positive regulator of the reproductive axis by stimulating gonadotrophin‐releasing hormone ( G n RH ) neurone activity in vertebrates. However, the precise mechanisms underlying the cyclic regulation of the kisspeptin neuroendocrine system remain largely unknown. The grass puffer, T akifugu niphobles , exhibits a unique spawning rhythm: spawning occurs 1.5–2 h before high tide on the day of spring tide every 2 weeks, and the spawning rhythm is connected to circadian and lunar‐/tide‐related clock mechanisms. The grass puffer has only one kisspeptin gene ( kiss2 ), which is expressed in a single neural population in the preoptic area ( POA ), and has one kisspeptin receptor gene ( kiss2r ), which is expressed in the POA and the nucleus dorsomedialis thalami. Both kiss2 and kiss2r show diurnal variations in expression levels, with a peak at Z eitgeber time ( ZT ) 6 (middle of day time) under the light/dark conditions. They also show circadian expression with a peak at circadian time 15 (beginning of subjective night‐time) under constant darkness. The synchronous and diurnal oscillations of kiss2 and kiss2r expression suggest that the action of K iss2 in the diencephalon is highly dependent on time. Moreover, midbrain G n RH 2 gene ( gnrh2 ) but not G n RH 1 or G n RH 3 genes show a unique semidiurnal oscillation with two peaks at ZT 6 and ZT 18 within a day. The cyclic expression of kiss2 , kiss2r and gnrh2 may be important in the control of the precisely‐timed diurnal and semilunar spawning rhythm of the grass puffer, possibly through the circadian clock and melatonin, which may transmit the photoperiodic information of daylight and moonlight to the reproductive neuroendocrine centre in the hypothalamus.