Advances in circadian clock regulation of reproduction

Circadian system coordination: new perspectives beyond classical models

Background

This review examines novel interaction mechanisms contributing to the robustness of circadian rhythms, focusing on enhanced communication between the suprachiasmatic nucleus (SCN) and peripheral clocks. While classical models explain biological clocks through molecular interactions and biochemical signaling, they incompletely account for several key features: precision maintenance despite cellular noise, rapid system-wide synchronization, and temperature compensation. We propose that the SCN, acting as a central hub, may utilize non-classical mechanisms to maintain robust synchronization of peripheral clocks, contributing to biological timekeeping stability. The clinical implications of this model are significant, potentially offering new approaches for treating circadian-related disorders through quantum-based interventions. Recent advances in quantum biosensors and diagnostic tools show promise for early detection and monitoring of circadian disruptions, while quantum-based therapeutic strategies may provide novel treatments for conditions ranging from sleep disorders to metabolic syndromes.

Aim of review

To evaluate classical models of circadian rhythm robustness and propose a novel synchronization model incorporating quantum mechanical principles, supported by recent advances in quantum biology and chronobiology, with emphasis on potential clinical applications.

Key scientific concepts

Recent research in quantum biology suggests potential mechanisms for enhanced circadian system coordination. The proposed model explores how quantum effects, including entanglement and coherence, may facilitate rapid system-wide synchronization and temporal coherence across tissues. These mechanisms could explain features not fully addressed by classical models: precision maintenance in noisy cellular environments, rapid resynchronization following environmental changes, temperature compensation of circadian periods, and sensitivity to weak electromagnetic fields. The framework integrates established chronobiology with quantum biological principles to explain system-wide temporal coordination and suggests new therapeutic approaches for circadian-related disorders.

Seasonal mRNA Expression of Circadian Clock Genes in the Lizard Brain

Seasonally breeding animals undergo physiological and behavioral changes to time reproduction to occur during specific seasons. These changes are regulated by changing environmental conditions, which may be communicated to the brain using the central circadian clock. This clock consists of a daily oscillation in the expression of several core genes, including period (per), cryptochrome (cry), circadian locomotor output cycles kaput (clock), and basic helix-loop-helix ARNT-like protein 1 (bmal1). We began to examine seasonal regulation of four core circadian clock genes in a dissection of the reptile brain containing the hypothalamus-per1, cry1, bmal1 and clock. Our study focused on examining mRNA expression in the morning and compared levels between breeding and nonbreeding animals. We found that per1 and bmal1 mRNA expression was highest in the nonbreeding compared to breeding season in the anole hypothalamus. We also found that cry1 mRNA expression was higher in the female compared to the male anole hypothalamus. We found support for the idea that core circadian genes play a role in regulating changes between the seasons and/or sexes, although more work is needed to elucidate what processes might be differentially regulated. To our knowledge, this is the first examination of the expression of these four genes in the reptilian brain.

Dynamic Transcriptional Regulation of the Hypothalamic-Pituitary-Testis Axis in the Seasonally Breeding Teleost Sebastes schlegelii

Spermatogenesis, the process of male germ cell development, is tightly regulated by the hypothalamic-pituitary-testis (HPT) axis in seasonally breeding teleosts. Despite its importance, our understanding of how the brain and male germ cells coordinate key transitions-such as testis initiation and maturation-remains limited, particularly in species with distinct seasonal reproductive cycles. Black rockfish (Sebastes schlegelii), a marine viviparous teleost, exhibits a prolonged testis quiescent phase lasting three-quarters of the year, with testis initiation occurring in September and maturation concluding in November and December. The mechanisms underlying these transitions are poorly characterized, leaving a critical gap in our knowledge of seasonal spermatogenesis and its regulation. Addressing this gap is crucial for advancing artificial breeding technologies, which could significantly benefit the aquaculture industry. RNA-seq was used to explore the gene regulatory networks involved in testis initiation in S. schlegelii. Transcriptomic analyses of brain and testis were conducted across key developmental phases. In the brain, upregulated genes were notably involved in neuroactive ligand-receptor interactions, whereas in the testis, differentially expressed genes were linked to cell cycle processes and ATP-dependent chromatin remodeling. Our findings reveal the molecular mechanisms underlying testis initiation in S. schlegelii, providing omics evidence for the role of the HPT axis in regulating this process. By elucidating the gene regulatory networks of the brain and testis during critical transitions, this study advances our understanding of spermatogenesis in seasonally breeding teleosts. These insights pave the way for developing year-round artificial breeding technologies, contributing to the sustainable management of commercially valuable fish species.

Influence of lifestyle and the circadian clock on reproduction

Background

The biological reproductive process requires the precise coordination of annual and daily signals to adapt to environmental shifts. Humans and animals have developed shared neuroendocrine systems that have adapted to process daily and seasonal light signals within the hypothalamic-pituitary -gonadal axis. However, the stability of circadian and seasonal biological processes is at risk due to industrialization and contemporary round-the-clock lifestyles. These threats include skipping breakfast, excessive artificial illumination during inappropriate hours because of irregular work schedules, nighttime urban lighting, and widespread environmental pollution from endocrine-disrupting chemicals. This review aimed to explore the interplay between lifestyle factors, circadian rhythms, and reproductive functions.

Methods

This review examined the reciprocal influences of circadian clocks on reproductive hormones, exploring the underlying mechanisms and their implications for fertility and reproductive health. We emphasized key findings regarding molecular clock components, endocrine pathways, and the critical importance of synchronizing circadian rhythms with hormonal cycles.

Main Findings

The intersection of reproductive endocrinology and circadian biology reveals complex interactions between hormonal regulation and circadian rhythms. Circadian rhythm misalignments due to environmental factors, including late-night work and skipping breakfast, negatively impact endocrine and reproductive functions.

Conclusions

More strategies are needed to mitigate the effects of circadian disruption on reproductive functions.

Vasoactive intestinal peptide excites GnRH neurons via KCa3.1, a potential player in the slow afterhyperpolarization current

Vasoactive intestinal peptide (VIP) is an important component of the suprachiasmatic nucleus (SCN) which relays circadian information to neuronal populations, including GnRH neurons. Human and animal studies have shown an impact of disrupted daily rhythms (chronic shift work, temporal food restriction, clock gene disruption) on both male and female reproduction and fertility. To date, how VIP modulates GnRH neurons remains unknown. Calcium imaging and electrophysiology on primary GnRH neurons in explants and adult mouse brain slice, respectively, were used to address this question. We found VIP excites GnRH neurons via the VIP receptor, VPAC2. The downstream signaling pathway uses both Gs protein/adenylyl cyclase/protein kinase A (PKA) and phospholipase C/phosphatidylinositol 4,5-bisphosphate (PIP2) depletion. Furthermore, we identified a UCL2077-sensitive target, likely contributing to the slow afterhyperpolarization current (IAHP), as the PKA and PIP2 depletion target, and the KCa3.1 channel as a specific target. Thus, VIP/VPAC2 provides an example of Gs protein-coupled receptor-triggered excitation in GnRH neurons, modulating GnRH neurons likely via the slow IAHP. The possible identification of KCa3.1 in the GnRH neuron slow IAHP may provide a new therapeutical target for fertility treatments.

Circadian clock gene BMAL1 regulates STAR expression in goose ovarian preovulatory granulosa cells

The ovarian circadian clock plays a regulatory role in the avian ovulation-oviposition cycle. However, little is known regarding the ovarian circadian clock of geese. In this study, we investigated rhythmic changes in clock genes over a 48-h period and identified potential clock-controlled genes involved in progesterone synthesis in goose ovarian preovulatory granulosa cells. The results showed that BMAL1, CRY1, and CRY2, as well as 4 genes (LHR, STAR, CYP11A1, and HSD3B) involved in progesterone synthesis exhibited rhythmic expression patterns in goose ovarian preovulatory granulosa cells over a 48-h period. Knockdown of BMAL1 decreased the progesterone concentration and downregulated STAR mRNA and protein levels in goose ovarian preovulatory granulosa cells. Overexpression of BMAL1 increased the progesterone concentration and upregulated the STAR mRNA level in goose ovarian preovulatory granulosa cells. Moreover, we demonstrated that the BMAL1/CLOCK complex activated the transcription of goose STAR gene by binding to an E-box motif. These results suggest that the circadian clock is involved in the regulation of progesterone synthesis in goose ovarian preovulatory granulosa cells by orchestrating the transcription of steroidogenesis-related genes.