Project description:Annual cycles in daylength provide an initial predictive environmental cue that plants and animals use to time seasonal biology. Seasonal changes in photoperiodic information acts to entrain endogenous programs in physiology to optimize an animal’s fitness. Attempts to identify the neural and molecular substrates of photoperiodic time measurement in birds have, to date, focussed on blunt changes in light exposure during a restricted period of photoinducibility. The objectives of these studies were first to characterise a molecular seasonal clock in Japanese quail and second, to identify the key transcripts involved in endogenously generated interval timing that underlies photosensitivity in birds. We hypothesized that the mediobasal hypothalamus (MBH) provides the neuroendocrine control of photoperiod-induced changes in reproductive physiology, and that the pars distalis of the pituitary gland contains an endogenous internal timer for the short photoperiod dependent development of reproductive photosensitivity. Here we report distinct seasonal waveforms of transcript expression in the MBH, and pituitary gland and discovered the patterns were not synchronized across tissues. Follicle-stimulating hormone-β (FSHβ) expression increased during the simulated spring equinox, prior to photoinduced increases in prolactin, thyrotropin-stimulating hormone-β and testicular growth. Diurnal analyses of transcript expression showed sustained elevated levels of FSHβ under conditions of the spring equinox, compared to autumnal equinox, short (<12L) and long (>12L) photoperiods. FSHβ expression increased in quail held in non-stimulatory short photoperiod, indicative of the initiation of an endogenously programmed interval timer. These data identify that FSHβ establishes a state of photosensitivity for the external coincidence timing of seasonal physiology. The independent regulation of FSHβ expression provides an alternative pathway through which other supplementary environmental cues, such as temperature, can fine tune seasonal reproductive maturation and involution.

Project description:The aim of this experiment was to explore transcriptomic changes in the gills of Altantic salmon (Salmo salar) following a model lab based parr smolt transformation from fresh water (FW) to salt water (SW). The process of smoltification (migration from FW to SW) is stimulated by long day photoperiod, which acts on the tissue-specific levels of active thyroid hormone (triiodothyronine, T3) through the expression of thyroid hormone type 2 deiodinase (dio2), responsible for conversion of inactive thyroxine (T4) to T3. To gain insight into the functional significance of dio2 induction, we performed a SW-challenge experiment in which we inhibited dio2 activity by addition of iopanoic acid (IOP) to the SW. We also assessed the ability of co-treatment with T3 to override IOP effects. Juvenile fish maintained in FW were subjected to a standard smolt photoperiod regime known to stimulate smoltification, after which they were randomly allocated to one of the four treatments: SW, SW+IOP, SW+IOP+T3 and FW as a control. Fish (n = 8-10 per treatment) were exposed to these conditions for 6 h and then sacrificed to obtain gill tissue for microarray analysis, carried out using a custom-designed Agilent oligonucleotide microarray platform Salar_2 (one glass slide with 4 x 44K arrays, Agilent design ID: 025520, array design A-MEXP-2065), developed and validated for Atlantic salmon (for details, see specific protocols) . In total, 36 hybridisations were performed on gills from individual fish, with 8-10 replicate fish per treatment. We identified 1939 genes whose expression was significantly increased or decreased by transfer from FW to SW. For a subset of 259 genes, this SW response was abolished if IOP was added to the SW, but maintained if T3 was also present during IOP treatment. This group of genes constitutes a candidate list, for which SW-inducibility appears to be dependent on locally mediated changes in gill T3 availability. The results of this experiment have been submitted for publication in Current Biology and are currently under review.

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Dissociating Mechanisms That Underlie Seasonal and Developmental Programs for the Neuroendocrine Control of Physiology in Birds

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