Circadian rhythms synchronize mitosis in Neurospora crassa

Abstract

The cell cycle and the circadian clock communicate with each other, resulting in circadian-gated cell division cycles. Alterations in this network may lead to diseases such as cancer. Therefore, it is critical to identify molecular components that connect these two oscillators. However, molecular mechanisms between the clock and the cell cycle remain largely unknown. A model filamentous fungus, Neurospora crassa, is a multinucleate system used to elucidate molecular mechanisms of circadian rhythms, but not used to investigate the molecular coupling between these two oscillators.In this report, we show that a conserved coupling between the circadian clock and the cell cycle exists via serine/threonine protein kinase-29 (STK-29), the Neurospora homolog of mammalian WEE1 kinase. Based on this finding, we established a mathematical model that predicts circadian oscillations of cell cycle components and circadian clock-dependent synchronized nuclear divisions. We experimentally demonstrate that G1 and G2 cyclins, CLN-1 and CLB-1, respectively, oscillate in a circadian manner with bioluminescence reporters. The oscillations of clb-1 and stk-29 gene expression are abolished in a circadian arrhythmic frq ko mutant. Additionally, we show the light-induced phase shifts of a core circadian component, frq, as well as the gene expression of the cell cycle components clb-1 and stk-29, which may alter the timing of divisions. We then used a histone hH1-GFP reporter to observe nuclear divisions over time, and show that a large number of nuclear divisions occur in the evening. Our findings demonstrate the circadian clock-dependent molecular dynamics of cell cycle components that result in synchronized nuclear divisions in Neurospora. M olecular mechanisms of circadian rhythms provide temporal information to other cellular processes, such as metabolism, to optimize their outcomes (1-3). For instance, circadian oscillations of rate-limiting genes in glucose metabolism suggest time-of-day specific regulatory mechanisms that maintain glucose homeostasis in mammals (3). Circadian clockgated cell division cycles have been observed in various organisms, including mammals, indicating that cell divisions preferentially occur at specific times of the day (4-7). In the mouse liver, expression of the cell cycle kinase-encoding gene, wee1, is directly activated by a heterodimeric circadian transcription factor, CLOCK-BMAL1, providing a molecular link between the cell cycle and circadian rhythms (5). This suggests that circadian clock-regulated WEE1 promotes periodic inhibition of mitotic cycles between G2 and M phase by phosphorylating and inactivating the mitotic cyclin-dependent kinase (CDK) (8). On the other hand, circadian-independent cell divisions have been reported in rat-1 fibroblasts despite the fact that these cells maintain robust circadian rhythms (9). These data suggest that not all cells with circadian rhythms may display circadian-gated cell division cycles.The multinucleate fungus Neurospora crassa has played a pivotal role i...

Intercellular Coupling of the Cell Cycle and Circadian Clock in Adult Stem Cell Culture

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“…The cell cycle consists of a series of phases, including DNA replication, various checkpoints and cell division, that allow cell proliferation. Previous studies in cyanobacteria, fungi, plant, zebrafish, and mammals have showed that circadian clocks influence the cell cycle to gate the timing of different phases of DNA synthesis, checkpoints, and cytokinesis (Dekens et al, 2003; Dong et al, 2010; Feillet et al, 2014; Hirayama et al, 2005; Hong et al, 2014; Kowalska et al, 2013; Laranjeiro et al, 2013; Masri et al, 2013; Matsu-Ura et al, 2016; Matsuo et al, 2003; Mori et al, 1996; Nagoshi et al, 2004). …”

Dissecting the Mechanisms of the Clock in Neurospora

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