Daily variation in melatonin synthesis and arylalkylamine N‐acetyltransferase activity in the nematode Caenorhabditis elegans

Abstract

Melatonin influences circadian rhythms and seasonal behavioral changes in vertebrates; it is synthesized from serotonin by N-acetylation by arylalkylamine N-acetyltransferase (AA-NAT) and O-methylation by N-acetylserotonin methyltransferase. However, its physiology and function in invertebrate models are less understood. In this work, we studied daily variations in melatonin synthesis and AA-NAT activity in the nematode Caenorhabditis elegans. Under light-dark conditions (LD), a rhythmic pattern of melatonin levels was observed, with higher levels toward the middle of the night, peaking at zeitgeber time (ZT) 18, and with a minimum value around ZT0-6. AA-NAT activity showed a diurnal and circadian fluctuation with higher levels of activity during the early night, both under LD and constant darkness conditions. A peak was found around ZT12 and circadian time (CT) 12. In addition, we investigated whether this nocturnal AA-NAT activity is inhibited by light. Our results show that both white and blue light pulses significantly inhibited AA-NAT activity at ZT18. This work demonstrates the daily fluctuation of melatonin synthesis and AA-NAT activity in the adult nematode C. elegans. In summary, this study takes additional advantage of an extremely useful invertebrate model system, which has only recently been exploited for circadian studies.

Circadian regulation of olfaction and an evolutionarily conserved, nontranscriptional marker in Caenorhabditis elegans

“…Over the last decade, there have been numerous reports of daily rhythms in the soil-dwelling nematode, C. elegans (6)(7)(8)(9)(10)(11)(12), although the connection between molecules and behavior has been lacking. Reasons for this may include a lack of known clock gene homologs as starting points, a number of low-amplitude behavioral rhythms, and the use of conditions that are far from ecological.…”

“…Previously, protocols used for clock research on the nematode, C. elegans (6)(7)(8)(9)(10)(11)(12), have shown circadian rhythms in behaviors (e.g., locomotor activity, defecation, and pharyngeal pumping rate), metabolism (e.g., resistance to osmotic stress), or the expression of hundreds of genes without a connection to rhythmic behaviors. Clearly, taken together, one would conclude that the nematode has a circadian system.…”

Aging signaling pathways and circadian clock-dependent metabolic derangements

“…First, pigment dispersing factor (PDF) and its receptor, which in insects play a role in transducing circadian oscillations to downstream processes (a function analogous to that of VIP: Vasoactive Intestinal Peptide in mammals) 51, 52 , have, been identified in C. elegans , and shown to be involved in circadian rhythmicity in locomotion 53 . Second, circadian cycling of the levels of melatonin and its synthase has recently been identified 54 , though not yet functionally characterized. Further downstream, profiling of genes expressed in rhythmic fashion during and after 12-hour light:dark or warm:cool cycles identified GO terms relating to a broad diversity of biological processes, chief among them metabolic processes, enriched in the genes that can be driven and/or entrained by cycling temperature in particular 42 .…”

Long-term imaging of circadian locomotor rhythms of a freely crawling C. elegans population

“…locomotor activity (Saigusa et al, 2002; Simonetta and Golombek, 2007), defecation and pharyngeal pumping rate (Migliori et al, 2011), metabolism e.g. resistance to osmotic stress (Kippert et al, 2002), and melatonin levels (Migliori et al, 2012). Although these studies indicate that C. elegans has a circadian system, little remains known about the molecular and neural components of the C. elegans circadian clock.…”