TY  - JOUR
A1  - Schwarzenberger, Anke
A1  - Wacker, Alexander
T1  - Melatonin synthesis follows a daily cycle in Daphnia
JF  - Journal of plankton research
N2  - In freshwater systems, Daphnia has been demonstrated to show adaptive responses following the light-dark cycle. The adjustment of these responses to the change of day and night is probably transmitted via the hormone melatonin. The rate-limiting enzyme in melatonin synthesis is the arylalkylamine N-transferase (AANAT). We identified three genes coding for insect-like AANATs in Daphnia, of which we measured the gene expression in an ecologically relevant light-dark cycle. We demonstrated that Daphnia's insect-like AANAT gene expression oscillated in a daily manner, and that the highest peak of expression after the onset of darkness was followed by a peak of melatonin production at midnight. Moreover, we could show an oscillation of endogenous melatonin synthesis in Daphnia. In most organisms, melatonin synthesis is due to rhythmic expression of genes of the circadian clock, since transcription of aanats is directly linked to a circadian transcription factor. We could demonstrate that putative clock genes and insect-like AANAT genes of Daphnia were equally expressed. Therefore, we propose that melatonin synthesis is coupled to the expression of Daphnia clock genes, and that insect-like AANATs of crustaceans have a similar function as AANATs of vertebrates: The initiation of melatonin synthesis. In future studies with Daphnia, it will be necessary to take the time of day into account since melatonin concentrations might influence stress responses.
KW  - arylalkylamine N-transferase
KW  - insect-like AANAT
KW  - qPCR
KW  - circadian clock
KW  - clock genes
Y1  - 2015
U6  - https://doi.org/10.1093/plankt/fbv029
SN  - 0142-7873
SN  - 1464-3774
VL  - 37
IS  - 3
SP  - 636
EP  - 644
PB  - Oxford Univ. Press
CY  - Oxford
ER  -