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Zebrafish serotonin N-acetyltransferase-2: marker
for development of pineal photoreceptors and circadian clock
function.
Gothilf Y, Coon SL, Toyama R, Chitnis A,
Namboodiri MA, Klein DC.
Section on Neuroendocrinology,
Laboratory of Developmental Neurobiology, National Institute of Child
Health and Human Development, National Institutes of Health, Bethesda,
Maryland 20892-4480, USA.
Serotonin N-acetyltransferase (AANAT),
the penultimate enzyme in melatonin synthesis, is typically found only
at significant levels in the pineal gland and retina. Large changes in
the activity of this enzyme drive the circadian rhythm in circulating
melatonin seen in all vertebrates. In this study, we examined the
utility of using AANAT messenger RNA (mRNA) as a marker to monitor the
very early development of pineal photoreceptors and circadian clock
function in zebrafish. Zebrafish AANAT-2 (zfAANAT-2) cDNA was isolated
and used for in situ hybridization. In the adult, zfAANAT-2 mRNA is
expressed exclusively in pineal cells and retinal photoreceptors.
Developmental analysis, using whole mount in situ hybridization,
indicated that pineal zfAANAT-2 mRNA expression is first detected at 22
h post fertilization. Retinal zfAANAT-2 mRNA was first detected on day 3
post fertilization and appears to be associated with development of the
retinal photoreceptors. Time-of-day analysis of 2- to 5-day-old
zebrafish larvae indicated that zfAANAT-2 mRNA abundance exhibits a
dramatic 24-h rhythm in a 14-h light, 10-h dark cycle, with high levels
at night. This rhythm persists in constant darkness, indicating that the
zfAANAT-2 mRNA rhythm is driven by a circadian clock at this stage. The
techniques described in this report were also used to determine that
zfAANAT-2 expression is altered in two well characterized genetic
mutants, mindbomb and floating head. The observations described here
suggest that zfAANAT-2 mRNA may be a useful marker to study development
of the pineal gland and of circadian clock mechanisms in
zebrafish.
PMID: 10499549 [PubMed - indexed for MEDLINE]
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