Research paperTemperature affects sexual maturation through the control of kisspeptin, kisspeptin receptor, GnRH and GTH subunit gene expression in the grass puffer during the spawning season
Introduction
Among the environmental factors, temperature plays an important role in the control of reproduction in vertebrates. Temperature directly affects molecular, biochemical, and physiological processes, especially in the ectothermic vertebrates (Pankhurst and King, 2010, Strussmann et al., 2010). In teleost fish, gonadal development, spawning and gonadal regression are greatly influenced by water temperature (Pankhurst and King, 2010, Wang et al., 2010, Okuzawa and Gen, 2013). Both anomalous increase and decrease in water temperature inhibit gonadal development, maturation and spawning. The increase in water temperature suppresses fish reproduction, decreases fish abundance and even induces extinction (Soria et al., 2008, Portner and Peck, 2010).
Ovarian development and maturation have been shown to be inhibited in above or below the temperature limit in a number of fish species (Wang et al., 2010). A decrease in water temperature showed limited accumulation of yolk and uncompleted or delayed final oocyte maturation in the blue gourami (Cheal and Davis, 1974) and mummichog (Cerda et al., 1996). Low temperature inhibited ovulation, reduced fecundity and size of vitellogenic oocytes in Prochilodus argenteus (Arantes et al., 2011). Both low and high temperature prevented gonadal development in the pikeperch (Hermelink et al., 2011). In the goldfish, ovulation induced by gonadotropin-releasing hormone (GnRH) was delayed with an increase in temperature (Rottmann and Shireman, 1985). However, the molecular and endocrine mechanisms that underlie these effects are poorly understood.
In fish, like other vertebrates, the central regulation of reproduction occurs through hypothalamus-pituitary-gonadal (HPG) axis. GnRH synthesized in the hypothalamus, regulates the synthesis and release of two gonadotropins (GTHs), follicle-stimulating hormone (FSH) and luteinizing hormone (LH), from the pituitary, which stimulate gonadal development and secretion of sex steroid hormones (Yaron et al., 2003, Zohar et al., 2010). It is now witnessed that kisspeptin plays an important role in the control of reproduction through regulating GnRH secretion in mammals. In teleost fish, kisspeptin and its receptor (Kissr, GPR54) system has been shown to have a stimulatory role in the control of reproduction (Parhar et al., 2004, Chang et al., 2012, Tena-Sempere et al., 2012, Zmora et al., 2012, Ohga et al., 2014, Espigares et al., 2015, Park et al., 2016). However, recently, it was demonstrated that the kisspeptin/Kissr system was dispensable for reproduction in zebrafish using gene knockout models (Tang et al., 2015). Furthermore, GnRH1 neurons do not co-express Kissr in medaka (Kanda et al., 2013). These results suggest that the physiological pathways that control reproduction are complex in fish, and kisspeptin may have a stimulatory role on GnRH neurons directly and/or indirectly via interneurons. It should be also noted that genes for kisspeptin and Kissr were diversified during the evolution of teleost fish, increasing the complexity of the kisspeptin/Kissr system (Kitahashi et al., 2009, Ogawa and Parhar, 2013). In the present study, however, the grass puffer (Takifugu niphobles), which has only a single set of genes for kisspeptin (kiss2) and Kissr (kiss2r) was utilized as a research model. Our previous studies on their expression in the hypothalamus and pituitary strongly support the concept that Kiss2 has an important role in the control of reproduction like other fishes mentioned above (Ando et al., 2013, Ando et al., 2014, Shahjahan et al., 2010).
The effects of temperature on the HPG axis have been examined in regard to GnRH and GTH subunit gene expression. Increase and decrease in water temperature (4 °C) suppresses gnrh3 mRNA levels in the blue gourami (David and Degani, 2011, Levy et al., 2011). The expression of gnrh1 in the brain and lhb in the pituitary was suppressed by high water temperature in the red seabream (Okuzawa and Gen, 2013). Elevated temperature also reduced fshb and lhb mRNA levels in the pejerrey (Soria et al., 2008). However, there is a paucity of information concerning the effect on kisspeptin, except one study in zebrafish, in which low and high temperature decreased kiss2 and gnrh3 mRNA levels (Shahjahan et al., 2013), and there is a clear need of further study to understand the effects of temperature on kisspeptin and its receptor gene expression.
The grass puffer shows unique reproductive physiology that is synchronized with seasonal, lunar and daily cycles. During the spawning season from spring to early summer, spawning occurs only during spring tide every two weeks (Motohashi et al., 2010, Ando et al., 2013). The fish usually aggregate at a certain seashore location for spawning 2–3.5 h before high tide at dusk, and spawning continues for 1–2 h before high tide during the rising tidal phase. Therefore, temperature as well as light, tide and time are considered to be important factors for the control of reproduction in the grass puffer (Ando et al., 2013). During the spawning periods, gnrh2, kiss2, kiss2r, lpxrfa and lpxrfa-r showed daily and circadian fluctuations in expression in the hypothalamus in association with the expression of melatonin receptor genes (Ikegami et al., 2009, Shahjahan et al., 2011, Ando et al., 2013, Ando et al., 2014), indicating the possible role of circadian clock and the pineal hormone, melatonin, in the control of reproduction of this species.
In our previous study, we found that gnrh1, kiss2 and kiss2r in the brain, and fshb and lhb in the pituitary showed seasonal fluctuations with gonadal development and regression (Shahjahan et al., 2010, Shahjahan et al., 2010, Ando et al., 2013). As a result, we hypothesized that a rise in water temperature in summer may trigger the end of the spawning season in the grass puffer. High water temperature leads to termination of the spawning period in the bitterling (Shimizu and Hanyu, 1982), honmoroko (Okuzawa et al., 1989) and pejerrey (Soria et al., 2008). Likewise, low temperature may postpone the commencement of spawning in Prochilodus argenteus (Arantes et al., 2011). Therefore, in the present study, we aimed to investigate the effects of low and high temperature on the expression of genes encoding kisspeptin (kiss2), kisspeptin receptor (kiss2r), three gonadotropin-releasing hormones (gnrh1, gnrh2 and gnrh3) and three gonadotropin subunits (gpa, fshb and lhb) in the grass puffer during the spawning period. We also examined the plasma levels of cortisol as an indicator of stress in fish during the experimental periods.
Section snippets
Fishes
Mature male grass puffer were collected at spawning grounds in Sado, Niigata in June for the 1st experiment, and in Kawana, Shizuoka in July for the 2nd experiment. The water temperature of sampling sites was 18 and 21 °C in Sado and Kawana, respectively. The fish were transferred to the Sado Marine Biological Station, Niigata University, Japan, and reared in indoor tanks (500 L) with flow of seawater under natural photoperiod (LD 14:10) for 2 weeks. The water temperature during the
Changes in GSI and expression of kiss2 in the 1st experiment
In the 1st experiment, the GSI showed no distinct changes in response to temperature changes in any exposure periods (Fig. 1A). The absolute amounts of kiss2 mRNA in the diencephalon/midbrain sample were examined by real-time PCR assay. In the day-3, no changes were observed in any temperature regime, while in the day-7, a decreasing tendency were observed in low temperature (11 °C), whereas an increasing tendency were observed in high temperature (25 °C) compared to the normal temperature (18 °C)
Discussion
To know the role of temperature in the regulation of reproductive function, we investigated the effects of exposure to low and high temperature on the expression of genes encoding kisspeptin, kisspeptin receptor and three GnRHs in the brain and genes encoding GTH subunits in the pituitary of sexually mature male grass puffer. In parallel to GSI, the kiss2 and kiss2r mRNA levels were significantly decreased by the low and high temperature exposures, concomitant with the decrease in gnrh1, fshb
Acknowledgments
We are grateful to Dr. Satoshi Awata, Mr. Tomonobu Uryu and Mr. Yoichiro Kato for their help in collecting fish. This study was supported by MEXT/JSPS KAKENHI grants (245700659 and 16H04812 to H.A.).
References (45)
- et al.
Molecular neuroendocrine basis of lunar-related spawning in grass puffer
Gen. Comp. Endocrinol.
(2013) - et al.
Influence of water temperature on induced reproduction by hypophysation, sex steroids concentrations and final oocyte maturation of the “curimata-pacu” Prochilodus argenteus (Pisces: Prochilodontidae)
Gen. Comp. Endocrinol.
(2011) - et al.
Pattern of vitellogenesis and follicle maturational competence during the ovarian follicular cycle of Fundulus heteroclitus
Gen. Comp. Endocrinol.
(1996) - et al.
Kisspeptin-1 directly stimulates LH and GH secretion from goldfish pituitary cells in a Ca2+-dependent manner
Gen. Comp. Endocrinol.
(2012) - et al.
Sexual behavior: social and ecological influences in the Anabantoid fish, Trichogaster trichopterus
Behav. Biol.
(1974) - et al.
Extrahypophyseal expression of gonadotropin subunits in pejerrey Odontesthes bonariensis and effects of high water temperatures on their expression
Gen. Comp. Endocrinol.
(2012) - et al.
Influence of temperature on puberty and maturation of pikeperch, Sander lucioperca
Gen. Comp. Endocrinol.
(2011) - et al.
Synchronized diurnal and circadian expressions of four subtypes of melatonin receptor genes in the diencephalon of a puffer fish with lunar-related spawning cycles
Neurosci. Lett.
(2009) - et al.
Effect of environmental temperature on growth- and reproduction-related hormones gene expression in the female blue gourami (Trichogaster trichopterus)
Comp. Biochem. Physiol. A: Mol. Integr. Physiol.
(2011) - et al.
Anatomy of the kisspeptin systems in teleosts
Gen. Comp. Endocrinol.
(2013)
Functional analysis of kisspeptin peptides in adult immature chub mackerel (Scomber japonicus) using an intracerebroventricular administration method
Neurosci. Lett.
Effects of photoperiod and temperature on gonadal maturation, and plasma steroid and gonadotropin levels in a cyprinid fish, the honmoroko Gnathopogon caerulescens
Gen. Comp. Endocrinol.
High water temperature impairs ovarian activity and gene expression in the brain-pituitary-gonadal axis in female red seabream during the spawning season
Gen. Comp. Endocrinol.
Year-to-year differences in plasma levels of steroid hormones in pre-spawning chum salmon
Gen. Comp. Endocrinol.
Kisspeptin2 stimulates the HPG axis in immature Nile tilapia (Oreochromis niloticus)
Comp. Biochem. Physiol. B: Biochem. Mol. Biol.
Stress and fish reproduction: the roles of allostasis and hormesis
Gen. Comp. Endocrinol.
Differential expression of three types of gonadotropin-releasing hormone genes during the spawning season in grass puffer, Takifugu niphobles
Gen. Comp. Endocrinol.
Elevation of Kiss2 and its receptor gene expression in the brain and pituitary of grass puffer during the spawning season
Gen. Comp. Endocrinol.
Temperature differentially regulates the two kisspeptin systems in the brain of zebrafish
Gen. Comp. Endocrinol.
Hypothalamic and dietary control of temperature-mediated longevity
Ageing Res. Rev.
Comparative insights of the kisspeptin/kisspeptin receptor system: lessons from non-mammalian vertebrates
Gen. Comp. Endocrinol.
Regulation of fish gonadotropins
Int. Rev. Cytol.
Cited by (54)
Transcriptomic response to GnRH down regulation by RNA interference in clam Ruditapes philippinarum, suggest possible role in reproductive function
2023, Comparative Biochemistry and Physiology -Part A : Molecular and Integrative PhysiologyScreening and characterization of X chromosome-specific markers in mandarin fish (Siniperca chuatsi)
2023, AquacultureCitation Excerpt :After the overwintering period, most of the nutrients taken by female fish need to be used for gonad development, while the male fish consume less nutrients of this (Liang, 1996), so the growth rate of male fish is faster than that of female fish at this stage. During the breeding period, female fish that reach sexual maturity will spawn naturally under the influence of external environmental factors such as temperature (Sunde et al., 2019; Shahjahan et al., 2017; Rahman et al., 2019). Postpartum female fish are easily infected with water molds and Oomycetes due to large consumption of nutrients and changes in body steroid hormone levels (Cao et al., 2012; van den Berg et al., 2013; Pickering and Pottinger, 1985), resulting in a large number of deaths of cultured individuals.