ABSTRACT
Kisspeptin is crucial for the generation of the circadian-gated preovulatory gonadotrophin-releasing hormone (GnRH)-LH surge in female rodents, with expression in the anteroventral periventricular nucleus (AVPV) peaking in the late afternoon of pro-oestrus. Given kisspeptin expression is established before puberty, the aim of the present study was to investigate kisspeptin and clock gene rhythms during the neonatal period. Anterior and posterior hypothalami were collected from C57BL/6J mice on Postnatal Days (P) 5, 15 and 25, at six time points across 24h, for analysis of gene expression by reverse transcription-quantitative polymerase chain reaction. Expression of aryl hydrocarbon receptor nuclear translocator-like gene (Bmal1) and nuclear receptor subfamily 1, group D, member 2 (Rev-erbα) in the anterior hypothalamus (containing the suprachiasmatic nucleus) was not rhythmic at P5 or P15, but Bmal1 expression exhibited rhythmicity in P25 females, whereas Rev-erbα expression was rhythmic in P25 males. KiSS-1 metastasis-suppressor (Kiss1) expression did not exhibit time-of-day variation in the anterior (containing the AVPV) or posterior (containing the arcuate nucleus) hypothalami in female and male mice at P5, P15 or P25. The data indicate that the kisspeptin circadian peak in expression observed in the AVPV of pro-oestrous females does not manifest at P5, P15 or P25, likely due to inadequate oestrogenic stimuli, as well as incomplete development of clock gene rhythmicity before puberty.
Subject(s)
CLOCK Proteins/metabolism , Circadian Rhythm/physiology , Gene Expression Regulation, Developmental , Hypothalamus/metabolism , Kisspeptins/metabolism , ARNTL Transcription Factors/genetics , ARNTL Transcription Factors/metabolism , Animals , CLOCK Proteins/genetics , Female , Kisspeptins/genetics , Male , Mice , Mice, Inbred C57BL , Nuclear Receptor Subfamily 1, Group D, Member 1/genetics , Nuclear Receptor Subfamily 1, Group D, Member 1/metabolism , Proestrus/genetics , Proestrus/metabolism , Receptors, Kisspeptin-1/genetics , Receptors, Kisspeptin-1/metabolism , Sex FactorsABSTRACT
Kisspeptin, the neuropeptide product of the Kiss1 gene, is critical in driving the hypothalamic-pituitary-gonadal (HPG) axis. Kisspeptin neurons in the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (Arc) of the hypothalamus mediate differential effects, with the Arc regulating negative feedback of sex steroids and the AVPV regulating positive feedback, vital for the preovulatory surge and gated under circadian control. We aimed to characterize hypothalamic Kiss1 and Kiss1r mRNA expression in nonpregnant and pregnant mice, and investigate potential circadian regulation. Anterior and posterior hypothalami were collected from C57BL/6J mice at diestrus, proestrus, and days 6, 10, 14, and 18 of pregnancy, at six time points across 24h, for real-time PCR analysis of gene expression. Analysis confirmed that Kiss1 mRNA expression in the AVPV increased at ZT13 during proestrus, with a luteinizing hormone surge observed thereafter. No diurnal regulation was seen at diestrus or at any stage of pregnancy. Anterior hypothalamic Avp mRNA expression exhibited no diurnal variation, but Avpr1a peaked at 12:00h during proestrus, possibly reflecting the circadian input from the suprachiasmatic nucleus to AVPV Kiss1 neurons. Rfrp (Npvf) expression in the posterior hypothalamus did not demonstrate diurnal variation at any stage. Clock genes Bmal1 and Rev-erbα were strongly diurnal, but there was little change between diestrus/proestrus and pregnancy. Our data indicate the absence of the circadian input to Kiss1 in pregnancy, despite high gestational estradiol levels and normal clock gene expression, and may suggest a disruption of a kisspeptin-specific diurnal rhythm that operates in the nonpregnant state.
