1) The expression of clock genes in the avian premammillary nucleus (PMM) was examined under short and long photoperiods to understand photoperiodic time measurement and its effects on seasonal reproduction. 2) Under long photoperiods, the Per3 gene was phase-delayed by 16 hours compared to short photoperiods. Cry1 and Per3 genes were also induced by light pulses at Zeitgeber time 14, the photosensitive phase. 3) In contrast, clock genes in the pineal gland and suprachiasmatic nucleus showed different patterns of expression depending on photoperiod and light pulses, suggesting they may not be directly associated with photosensitivity and reproduction

1. ORIGINAL ARTICLE
Photoperiodic Modulation of Clock Gene Expression in the Avian
Premammillary Nucleus
B. Leclerc,*1
S. W. Kang,*1
L. J. Mauro,* S. Kosonsiriluk,* Y. Chaiseha and M. E. El Halawani*
*Department of Animal Science, University of Minnesota, St Paul, MN, USA.
School of Biology, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima, Thailand.
The seasonal rhythms of endocrine and metabolic physiological pro-
cesses in breeding birds are known to be synchronised by the per-
ception of environmental cues such as day length (1, 2). The timing
of neuroendocrine events important for avian reproduction is set
by internal clocks and by deep brain photoreceptors that receive
and integrate this photoperiodic information (3, 4). Shifts in timing
as a result of input from these structures will result in the modula-
tion of endocrine-related gene expression, which will drive the
function of the reproductive organs.
The location of the clocks or circadian oscillators and the photo-
receptors responsible for reproductive photoperiodic time measure-
ment (PTM) in birds is unknown. The medial basal hypothalamic
Journal of
Neuroendocrinology
Correspondence to:
Mohamed E. El Halawani, 495
AnSci ⁄ VetMed, 1988 Fitch Avenue,
St Paul, MN 55108, USA (e-mail:
elhal001@umn.edu).
1
B.L. and S.W.K. contributed equally to
this study.
The premammillary nucleus (PMM) has been shown to contain a daily endogenous dual-oscilla-
tion in dopamine (DA) ⁄ melatonin (MEL) as well as c-fos mRNA expression that is associated
with the daily photo-inducible phase of gonad growth in turkeys. In the present study, the
expression of clock genes (Bmal1, Clock, Cry1, Cry2, Per2 and Per3) in the PMM was determined
under short (8 : 16 h light ⁄ dark cycle) and long (16 : 8 h light ⁄ dark cycle) photoperiods relative
to changes associated with the diurnal rhythm of DA and MEL. Constant darkness (0 : 24 h
light⁄ dark cycle) was used to assess the endogenous response of clock genes. In addition, light
pulses were given at zeitgeber time (ZT) 8, 14 and 20 to ascertain whether clock gene expression
is modulated by light pulse stimulation and therefore has a daily phase-related response. In the
PMM, the temporal clock gene expression profiles were similar under short and long photoperi-
ods, except that Per3 gene was phase-delayed by approximately 16 h under long photoperiod.
In addition, Cry1 and Per3 genes were light-induced at ZT 14, the photosensitive phase for
gonad recrudescence, whereas the Clock gene was repressed. Gene expression in established cir-
cadian pacemakers, the visual suprachiasmatic nucleus (vSCN) and the pineal, was also deter-
mined. Clock genes in the pineal gland were rhythmic under both photoperiods, and were not
altered after light pulses at ZT 14, which suggests that pineal clock genes may not be associated
with the photosensitive phase and reproductive activities. In the vSCN, clock gene expression
was phase-shifted depending on the photoperiod, with apexes at night under short day length
and during the day under long day length. Furthermore, light pulses at ZT 14 induced the Per2
gene, whereas it repressed the Bmal1 gene. Taken together, the changes in clock gene expres-
sion observed within the PMM were unique compared to the pineal and vSCN, and were
induced by long photoperiod and light during the daily photosensitive phase; stimuli that are
also documented to promote reproductive activity. These results show that Cry1 and Per3 are
involved in the photic response associated with the PMM neuronal activation and are coincident
with an essential circadian mechanism (photosensitive phase) controlling the reproductive neu-
roendocrine system.
Key words: light pulse, clock genes, DA-MEL neurones, PMM, birds, seasonal reproduction.
doi: 10.1111/j.1365-2826.2009.01942.x
Journal of Neuroendocrinology 22, 119–128
ª 2010 The Authors. Journal Compilation ª 2010 Blackwell Publishing Ltd
Journal of Neuroendocrinology
From Molecular to Translational Neurobiology