Synchronised Expressions of LPXRFamide Peptide and its Receptor Genes: Seasonal, Diurnal and Circadian Changes During Spawning Period in Grass Puffer

Abstract

Among the RFamide peptide family, the LPXRFamide peptide (LPXRFa) group regulates the release of various pituitary hormones and, recently, LPXRFa genes were found to be regulated by photoperiod via melatonin. As a first step towards investigating the role of LPXRFa on reproductive function in grass puffer (Takifugu niphobles), which spawns in semilunar cycles, genes encoding LPXRFa and its receptor (LPXRFa-R) were cloned, and seasonal, diurnal and circadian changes in their absolute amounts of mRNAs in the brain and pituitary were examined by quantitative real-time polymerase chain reaction. The grass puffer LPXRFa precursor contains two putative RFamide peptides and one possible RYamide peptide. LPXRFa and LPXRFa-R genes were extensively expressed in the diencephalon and pituitary. The expression levels of both genes were significantly elevated during the spawning periods in both sexes in the brain and pituitary, although they were low in the spawning fish just after releasing eggs and sperm. The treatment of primary pituitary cultures with goldfish LPXRFa increased the amounts of follicle-stimulating hormone β- and luteinising hormone β-subunit mRNAs. In the diencephalon, LPXRFa and LPXRFa-R genes showed synchronised diurnal and circadian variations with one peak at zeitgeber time 3 and circadian time 15, respectively. The correlated expression patterns of LPXRFa and LPXRFa-R genes in the diencephalon and pituitary and the possible stimulatory effects of LPXRFa on gonadotrophin subunit gene expression suggest the functional significance of the LPXRFa and LPXRFa-R system in the regulation of lunar-synchronised spawning of grass puffer.

GnIH plays a negative role in regulating GtH expression in the common carp, Cyprinus carpio L.

“…Considering the changes in GnIH mRNA during reproduction, we concluded that GnIH plays a negative role in regulating GtH in the common carp. The results are consistent to those for the zebrafish and goldfish (Qi et al, 2013;Zhang et al, 2010), but opposite to the results obtained for the grass puffer, tilapia, and salmon (Amano et al, 2006;Biran et al, 2014;Shahjahan et al, 2011). The differing results may be related to the protein sequence of common carp GnIH compared with those of the goldfish, zebrafish, grass puffer, and tilapia.…”

“…However, there different kinds of GnIHRs existed. In goldfish, zebrafish and common carp, three kinds of GnIHRs were found, but grass puffer and tilapia have only one receptor (Biran et al, 2014;Qi et al, 2013;Shahjahan et al, 2011;Zhang et al, 2010). Different numbers of GnIH receptors may also contribute to different functions of GnIH in teleosts.…”

“…However, when incubating sockeye salmon (Oncorhynchus nerka) pituitary cell with different doses of goldfish GnIH-I/II/III peptides, FSH, LH, and GH concentrations increased significantly (Amano et al, 2006). In the grass puffer (Takifugu niphobles), incubation of pituitary cells with different doses of goldfish GnIH-I resulted in an increase in FSH and LH mRNA levels (Shahjahan et al, 2011). Administration of the GnIH-II peptide to tilapia pituitary cells or intraperitoneal injection of female tilapia resulted in an increase in FSH and LH proteins (Biran et al, 2014).…”

“…In zebrafish, GnIH peptides were called GnIH-1/2/3 (Qi et al, 2013). However, GnIH peptides were called LPXRFa-1/2/3 because of the conserved LPXRF sequence at the C-terminal, but most peptides in tilapia and grass puffer do not contained the LPXRFa (Biran et al, 2014;Shahjahan et al, 2011).…”

“…So far, GnIH cDNA sequences have been identified in goldfish, grass puffer, zebrafish and tilapia (Biran et al, 2014;Shahjahan et al, 2011;Sawada et al, 2002;Zhang et al, 2010). In most of these reports, GnIH peptides were named LPXRFa-1/2/3.…”