G1/S cell cycle regulators mediate effects of circadian dysregulation on tumor growth and provide targets for timed anticancer treatment.

Circadian disruption has multiple pathological consequences, but the underlying mechanisms are largely unknown. To address such mechanisms, we subjected transformed cultured cells to chronic circadian desynchrony (CCD), mimicking a chronic jet-lag scheme, and assayed a range of cellular functions. The results indicated a specific circadian clock-dependent increase in cell proliferation. Transcriptome analysis revealed up-regulation of G1/S phase transition genes (myelocytomatosis oncogene cellular homolog [Myc], cyclin D1/3, chromatin licensing and DNA replication factor 1 [Cdt1]), concomitant with increased phosphorylation of the retinoblastoma (RB) protein by cyclin-dependent kinase (CDK) 4/6 and increased G1-S progression. Phospho-RB (Ser807/811) was found to oscillate in a circadian fashion and exhibit phase-shifted rhythms in circadian desynchronized cells. Consistent with circadian regulation, a CDK4/6 inhibitor approved for cancer treatment reduced growth of cultured cells and mouse tumors in a time-of-day-specific manner. Our study identifies a mechanism that underlies effects of circadian disruption on tumor growth and underscores the use of treatment timed to endogenous circadian rhythms.

Asymmetric vasopressin signaling spatially organizes the master circadian clock.

The suprachiasmatic nucleus (SCN) is the neural network that drives daily rhythms in behavior and physiology. The SCN encodes environmental changes through the phasing of cellular rhythms across its anteroposterior axis, but it remains unknown what signaling mechanisms regulate clock function along this axis. Here we demonstrate that arginine vasopressin (AVP) signaling organizes the SCN into distinct anteroposterior domains. Spatial mapping of SCN gene expression using in situ hybridization delineated anterior and posterior domains for AVP signaling components, including complementary patterns of V1a and V1b expression that suggest different roles for these two AVP receptors. Similarly, anteroposterior patterning of transcripts involved in Vasoactive Intestinal Polypeptide- and Prokineticin2 signaling was evident across the SCN. Using bioluminescence imaging, we then revealed that inhibiting V1A and V1B signaling alters period and phase differentially along the anteroposterior SCN. V1 antagonism lengthened period the most in the anterior SCN, whereas changes in phase were largest in the posterior SCN. Further, separately antagonizing V1A and V1B signaling modulated SCN function in a manner that mapped onto anteroposterior expression patterns. Lastly, V1 antagonism influenced SCN period and phase along the dorsoventral axis, complementing effects on the anteroposterior axis. Together, these results indicate that AVP signaling modulates SCN period and phase in a spatially specific manner, which is expected to influence how the master clock interacts with downstream tissues and responds to environmental changes. More generally, we reveal anteroposterior asymmetry in neuropeptide signaling as a recurrent organizational motif that likely influences neural computations in the SCN clock network.

An LHX1-Regulated Transcriptional Network Controls Sleep/Wake Coupling and Thermal Resistance of the Central Circadian Clockworks.

The suprachiasmatic nucleus (SCN) is the central circadian clock in mammals. It is entrained by light but resistant to temperature shifts that entrain peripheral clocks [1-5]. The SCN expresses many functionally important neuropeptides, including vasoactive intestinal peptide (VIP), which drives light entrainment, synchrony, and amplitude of SCN cellular clocks and organizes circadian behavior [5-16]. The transcription factor LHX1 drives SCN Vip expression, and cellular desynchrony in Lhx1-deficient SCN largely results from Vip loss [17, 18]. LHX1 regulates many genes other than Vip, yet activity rhythms in Lhx1-deficient mice are similar to Vip-/- mice under light-dark cycles and only somewhat worse in constant conditions. We suspected that LHX1 targets other than Vip have circadian functions overlooked in previous studies. In this study, we compared circadian sleep and temperature rhythms of Lhx1- and Vip-deficient mice and found loss of acute light control of sleep in Lhx1 but not Vip mutants. We also found loss of circadian resistance to fever in Lhx1 but not Vip mice, which was partially recapitulated by heat application to cultured Lhx1-deficient SCN. Having identified VIP-independent functions of LHX1, we mapped the VIP-independent transcriptional network downstream of LHX1 and a largely separable VIP-dependent transcriptional network. The VIP-independent network does not affect core clock amplitude and synchrony, unlike the VIP-dependent network. These studies identify Lhx1 as the first gene required for temperature resistance of the SCN clockworks and demonstrate that acute light control of sleep is routed through the SCN and its immediate output regions.

Tanycytes of the hypothalamic median eminence form a diet-responsive neurogenic niche.

Adult hypothalamic neurogenesis has recently been reported, but the cell of origin and the function of these newborn neurons are unknown. Using genetic fate mapping, we found that median eminence tanycytes generate newborn neurons. Blocking this neurogenesis altered the weight and metabolic activity of adult mice. These findings reveal a previously unreported neurogenic niche in the mammalian hypothalamus with important implications for metabolism.