Molecular and Neural Mechanisms of Temperature Preference Rhythm in Drosophila melanogaster

Abstract

Temperature influences animal physiology and behavior. Animals must set an appropriate body temperature to maintain homeostasis and maximize survival. Mammals set their body temperatures using metabolic and behavioral strategies. The daily fluctuation in body temperature is called the body temperature rhythm (BTR). For example, human body temperature increases during wakefulness and decreases during sleep. BTR is controlled by the circadian clock, is closely linked with metabolism and sleep, and entrains peripheral clocks located in the liver and lungs. However, the underlying mechanisms of BTR are largely unclear. In contrast to mammals, small ectotherms, such as Drosophila, control their body temperatures by choosing appropriate environmental temperatures. The preferred temperature of Drosophila increases during the day and decreases at night; this pattern is referred to as the temperature preference rhythm (TPR). As flies are small ectotherms, their body temperature is close to that of the surrounding environment. Thus, Drosophila TPR produces BTR, which exhibits a pattern similar to that of human BTR. In this review, we summarize the regulatory mechanisms of TPR, including recent studies that describe neuronal circuits relaying ambient temperature information to dorsal neurons (DNs). The neuropeptide diuretic hormone 31 (DH31) and its receptor (DH31R) regulate TPR, and a mammalian homolog of DH31R, the calcitonin receptor (CALCR), also plays an important role in mouse BTR regulation. In addition, both fly TPR and mammalian BTR are separately regulated from another clock output, locomotor activity rhythms. These findings suggest that the fundamental mechanisms of BTR regulation may be conserved between mammals and flies. Furthermore, we discuss the relationships between TPR and other physiological functions, such as sleep. The dissection of the regulatory mechanisms of Drosophila TPR could facilitate an understanding of mammalian BTR and the interaction between BTR and sleep regulation.

Keywords: Drosophila melanogaster; body temperature rhythm; calcitonin receptor; circadian clock; circadian rhythms; diuretic hormone 31; dorsal neurons; temperature preference rhythm.

Figure 1.

Human BTR and fly TPR. (a) Daily human core body temperature fluctuation (figures replotted using an example from Duffy et al., 1998, Figure 3). (b) Drosophila TPR (figures replotted using an example from Kaneko et al., 2012, Figure 1). (c) The inverse proportionality between daily fluctuations in core body temperature and sleep propensity in humans (figure replotted using an example from Lack et al., 2008, Figure 1). The black line and dashed line in the graph represent human core body temperature and sleep propensity, respectively. The shadowed areas in the graphs in (a) and (c) or in (b) indicate a period of sleep or nighttime, respectively. Abbreviations: BTR = body temperature rhythm; TPR = temperature preference rhythm; ZT = zeitgeber time.

Figure 2.

Drosophila TPR. (a) The apparatus for the Drosophila temperature preference behavior assay (modified from Goda and Hamada, 2019, Figure 2). Peltier devices are set on the bottom of the apparatus to heat and cool the metal plate. A plexiglass cover is placed on the plate, and air chambers are made between the plate and the cover with a temperature gradient from 18 to 32 °C. Flies enter the chambers through the holes on the cover. (b) Drosophila temperature preference behavior assay. Thirty minutes after the flies entered the chambers, they settled at the preferred temperature locations in the chambers. Flies avoid noxious cold and warm temperatures, and then they determine their Tp by the balance between cold and warm avoidance behaviors. TRPA1 is a warm-sensing molecule that is used for warm avoidance behavior (Hamada et al., 2008). (c, d) TPR in w¹¹¹⁸ (c) and per⁰¹ (d) flies (figure replotted using an example from Kaneko et al., 2012, Figure 2). The red and blue lines show TPR under LD and DD, respectively. The temperature preference assays were not performed continuously for 24 h; instead, they were independently performed for 30 min at different times of the day. The flies used for the behavioral assay were never reused. More than five trials were performed in each time interval, and the preferred Tp and SEM were calculated (Goda et al., 2014). The shadowed areas in the graphs represent nighttime. Abbreviations: TPR = temperature preference rhythm; TRPA1 = transient receptor potential cation channel A1; LD = light-dark; DD = dark-dark. Color version of the figure is available online. *p < 0.05. **p < 0.01. ***p < 0.001 (comparison with ZT 1-3).

Figure 3.

Core clock cells receive temperature inputs. (a) The core clock cells in the fly brain hemisphere (b) The warm- and cold-sensing neurons responsible for temperature preference behavior in the brain. ACs are warm-sensing neurons located at the antennal nerve between the antenna and the brain, and cold-sensing neurons are located in the antenna (modified from Umezaki 2019, Biomedical gerontology). (c) A schematic diagram of the current model for thermosensation and TPR regulation in Drosophila. In this model, the DN2-DN1p microcircuit and DN1as are responsible for TPR, and the DN2-DN1p microcircuit also regulates the Tp setpoint. In DN2-DN1p microcircuits, DN1ps receive clock information from DN2s and warm-temperature information from ACs (red arrowhead). DN1ps also receive warm- and cold-temperature information from peripheral thermosensors. In addition, cold-temperature information from the peripheral thermosensors is transferred to DN1as through TPNIIs (blue arrowhead). Warm and cold stimuli change the neuronal activities in DN1ps and DN2s (gray dotted arrowheads). The red and blue arrows represent warm- and cold-temperature information pathways, respectively. Abbreviations: AC = anterior cell; TPR = temperature preference rhythm; DN1a = anterior dorsal neuron 1; DN1p = posterior dorsal neuron 1; DN2 = dorsal neuron 2; DN3 = dorsal neuron 3; sLNv = small ventrolateral neuron; lLNv = large ventrolateral neuron; 5th-sLNv = fifth small ventrolateral neuron; LNd = dorsolateral neuron; LPN = lateral posterior neuron; TPN = thermosensory projection neuron; TPNII = type II TPN. Color version of the figure is available online.

Figure 4.

TPR phenotypes of Dh31r, Dh31, and Pdf mutant flies and models for molecular mechanisms of TPR regulation. TPR in Dh31r mutant (a: orange line), Dh31 mutant (b: blue line), and Pdf mutant (c: green line) flies compared with w¹¹¹⁸ flies (a-c: gray line) (replotted using an example from Goda et al., 2018, Figure 1 (a) and Goda et al., 2016, Figure 3 (b, c)). The shadowed areas in the graphs represent nighttime. *p < 0.05. **p < 0.01. ***p < 0.001 (compared with ZT 1-3, only daytime)(d) Schematic diagrams of the daytime (ZT 0-12), night-onset (ZT9-12 to ZT13-15), and predawn Tp (ZT 21-24) regulations (modified from Goda and Hamada, 2019, Figure 7). Abbreviations: TPR = temperature preference rhythm; Tp = preferred temperature; ZT = zeitgeber time; DH31R = diuretic hormone 31 receptor; PDF = pigment dispersing factor. Color version of the figure is available online.

Figure 5.

Mammal CALCR and Drosophila DH31R regulate BTR. (a) The BTR in LD cycles in control (blue line) and Calcr knockout (red line) mice (modified from Goda et al., 2018, Figure 6). The bars at the top of the graph represent light (white bar) and dark (black bar) cycles. The body temperatures in the middle of the night are significantly different between control and Calcr knockout mice. *p < 0.05 (comparison between Calcr knockout and control mice at ZT 20). (b) A schematic diagram showing the evolutionally conserved function of the calcitonin receptor for BTR in Drosophila and mammals. Calcitonin receptors in both Drosophila and mammals are responsible for BTR regulation but not for locomotor activity rhythms. Abbreviations: CALCR = calcitonin receptor; DH31R = diuretic hormone 31 receptor; BTR = body temperature rhythm; LD = light-dark; TPR = temperature preference rhythm. Color version of the figure is available online.