[Frontiers in Bioscience 15, 1040-1074, June 1, 2010]

Circadian clocks in crustaceans: identified neuronal and cellular systems

Johannes Strauss, Heinrich Dircksen

Department of Zoology, Stockholm University, Svante Arrhenius vag 18A, S-10691 Stockholm, Sweden


1. Abstract
2. Introduction
2. Introduction: crustacean circadian biology
2.1. Rhythms and circadian phenomena
2.2. Chronobiological systems in Crustacea
2.3. Pacemakers in crustacean circadian systems
3. The cellular basis of crustacean circadian rhythms
3.1. The retina of the eye
3.1.1. Eye pigment migration and its adaptive role
3.1.2. Receptor potential changes of retinular cells in the electroretinogram (ERG)
3.2. Eyestalk systems and mediators of circadian rhythmicity
3.2.1. Red pigment concentrating hormone (RPCH)
3.2.2. Crustacean hyperglycaemic hormone (CHH)
3.2.3. Pigment-dispersing hormone (PDH)
3.2.4. Serotonin
3.2.5. Melatonin
3.2.6. Further factors with possible effects on circadian rhythmicity
3.3. The caudal photoreceptor of the crayfish terminal abdominal ganglion (CPR)
3.4. Extraretinal brain photoreceptors
3.5. Integration of distributed circadian clock systems and rhythms
4. Comparative aspects of crustacean clocks
4.1. Evolution of circadian pacemakers in arthropods
4.2. Putative clock neurons conserved in crustaceans and insects
4.3. Clock genes in crustaceans
4.3.1. Current knowledge about insect clock genes
4.3.2. Crustacean clock-gene
4.3.3. Crustacean period-gene
4.3.4. Crustacean cryptochrome-gene
5. Perspective
6. Acknowledgements
7. References


Circadian rhythms are known for locomotory and reproductive behaviours, and the functioning of sensory organs, nervous structures, metabolism and developmental processes. The mechanisms and cellular bases of control are mainly inferred from circadian phenomenologies, ablation experiments and pharmacological approaches. Cellular systems for regulation summarised here comprise the retina, the eyestalk neuroendocrine X-organ-sinus gland system, several neuropeptides such as red pigment concentrating, hyperglycaemic and pigment-dispersing hormones, and factors such as serotonin and melatonin. No master clock has been identified, but a model of distributed clockwork involves oscillators such as the retinular cells, neurosecretory systems in the optic lobes, putative brain pacemakers, and the caudal photoreceptor. Extraretinal brain photoreceptors mediate entrainment. Comparative analyses of clock neurons and proteins known from insects may allow the identification of candidate clock neurons in crustaceans as putative homologues in the two taxa. Evidence for the existence of "insect-like" intracellular clock proteins and (light sensitive) transcription factors is scarce, but clock-, period-, and cryptochrome-gene products have been localised in the CNS and other organs rendering further investigations into crustacean clockwork very promising.