Daily expression of clock genes in central and peripheral tissues of tree sparrow (<i>Passer montanus</i>)
Creators: name: Zothanmawii Renthlei
name: Tennison Gurumayum
name: Borah, Bijoy Krishna
name: Trivedi, Amit Kumar
Publisher: name: Taylor & Francis
Year: 2018
Subjects: subject: Biochemistry
subject: Medicine
subject: Genetics
subject: FOS: Biological sciences
subject: FOS: Biological sciences
subject: Molecular Biology
subject: Neuroscience
subject: Physiology
subject: 39999 Chemical Sciences not elsewhere classified
subject: FOS: Chemical sciences
subject: FOS: Chemical sciences
subject: Ecology
subject: 69999 Biological Sciences not elsewhere classified
subject: Developmental Biology
subject: 110309 Infectious Diseases
subject: FOS: Health sciences
subject: FOS: Health sciences
subject: 60506 Virology

description: Almost all organisms live in a fluctuating environment. To achieve synchrony with the fluctuating environment, organisms have evolved with time-tracking mechanism commonly known as biological clocks. This circadian clock machinery has been identified in almost all cells of vertebrates and categorized as central and peripheral clocks. In birds, three independent circadian clocks reside within the nervous tissues in the hypothalamus, pineal and retina, which interact with each other and produce circadian time at a functional level. There is limited knowledge available of the molecular clockwork, and of integration between central and peripheral clocks in birds. Here, we studied daily expression of canonical clock genes (<i>Bmal1, Clock, Per2, Per3, Cry1</i> and <i>Cry2</i>) and clock-controlled gene (<i>Npas2</i>) in all three central tissues (hypothalamus, pineal and retina) and in peripheral tissues (liver, intestine and muscle). Wild caught adult male tree sparrows were exposed to equinox photoperiod (12L:12D) for 2 weeks and after that birds were sacrificed (<i>N</i> = 5 per time point) at six time points (ZT1, ZT5, ZT9, ZT13, ZT17 and ZT21; ZT0 is lights on). Daily expression of clock genes was studied using qPCR. <i>Bmal1, Clock, Per2, Per3, Cry1, Cry2</i> and <i>Npas2</i> showed daily oscillation in all tissues except <i>Cry2</i> in hypothalamus, pineal and intestine. We observed tissue-specific expression pattern for all clock and clock-controlled genes. <i>Bmal1</i> transcripts expressed during early phase of night. <i>Clock</i> acrophase was observed during middle or late day time in the central clock while during early-to-middle phase of night in peripheral tissues. <i>Npas2</i> expression pattern was similar to <i>Bmal1. Per</i> genes peaked either late at night or early during day time. However, <i>Cry</i> genes were peaked <b>either at late day time (<i>Cry1</i>in retina, liver and intestine; <i>Cry2</i> in liver and intestine) or at early night phase (<i>Cry1</i> in hypothalamus, pineal and muscle; <i>Cry2</i> in hypothalamus, pineal, retina and muscle)</b>. Our results are consistent with the autoregulatory circadian feedback loop, and suggest a conserved tissue-level circadian time generation in tree sparrows. Change in peak expression timing of these genes in different tissues implicates tissue-specific contribution of individual clock genes in the circadian time generation.