Heterogeneity of the Peripheral Circadian Systems in Drosophila melanogaster: A Review

Abstract

Circadian rhythms in organisms are involved in many aspects of metabolism, physiology, and behavior. In many animals, these rhythms are produced by the circadian system consisting of a central clock located in the brain and peripheral clocks in various peripheral tissues. The oscillatory machinery and entrainment mechanism of peripheral clocks vary between different tissues and organs. The relationship between the central and peripheral clocks is also tissue-dependent. Here we review the heterogeneous nature of peripheral circadian clocks in the fruit fly Drosophila melanogaster and their dependence on the central clock, and discuss their significance in the temporal organization of physiology in peripheral tissues/organs.

Keywords: Drosophila; circadian clock; circadian rhythm; cryptochrome; molecular oscillatory mechanism; peripheral oscillator; physiological rhythms.

Figure 1

Function of CRY in peripheral circadian clocks and the relationship between central and peripheral clocks in Drosophila melanogaster. (A) The functions of CRY vary in peripheral circadian clocks. In most peripheral circadian systems, CRY functions as a photoreceptor (^*) and a core component (^**) of the clock. However, CRY acts as a photoreceptor (^*), but not as a core component of the clock, in the epidermis, which controls cuticle deposition rhythm, and in the prothoracic gland (PG). CLK, CLOCK; CRY, CRYPTOCHROME; CYC, CYCLE; per, period; tim, timeless. (B) Various relationships between central and peripheral clocks. (a) Most peripheral oscillators are independent of the central clock. (b) Some peripheral oscillators, such as oenocyte oscillators, are a slave to the central clock, receiving phase information to maintain an appropriate phase relationship to the central clock. (c) Some peripheral oscillators, such as those in PG, receive light and temporal signals from the central clock to drive oscillation and coordinate molecular oscillation. See Table 1 for more examples.