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  - 
TY  - JOUR
A1  - Koussoroplis, Apostolos-Manuel
A1  - Schwarzenberger, Anke
A1  - Wacker, Alexander
T1  - Diet quality determines lipase gene expression and lipase/esterase activity in Daphnia pulex
JF  - Biology open : BiO
N2  - We studied the short- (12 h) and long-term (144 h) response of Daphnia pulex lipases to quality shifts in diets consisting of different mixtures of the green alga Scenedesmus with the cyanobacterium Synechococcus, two species with contrasting lipid compositions. The lipase/esterase activity in both the gut and the body tissues had fast responses to the diet shift and increased with higher dietary contributions of Synechococcus. When screening the Daphnia genome for TAG lipases, we discovered a large gene-family expansion of these enzymes. We used a subset of eight genes for mRNA expression analyses and distinguished between influences of time and diet on the observed gene expression patterns. We identified five diet-responsive lipases of which three showed a sophisticated short- and long-term pattern of expression in response to small changes in food-quality. Furthermore, the gene expression of one of the lipases was strongly correlated to lipase/esterase activity in the gut suggesting its potentially major role in digestion. These findings demonstrate that the lipid-related enzymatic machinery of D. pulex is finely tuned to diet and might constitute an important mechanism of physiological adaptation in nutritionally complex environments.
KW  - Cyanobacteria
KW  - Digestive enzyme activity
KW  - Nutritional quality
KW  - Lipases
Y1  - 2017
U6  - https://doi.org/10.1242/bio.022046
VL  - 6
SP  - 210
EP  - 216
PB  - The company of Biologists
CY  - Cambridge
ER  -