Seasonal alterations in the daily rhythms in hypothalamic expression of genes involved in the photoperiodic transduction and neurosteroid‐dependent processes in migratory blackheaded buntings

Abstract

The present study investigated seasonal alterations in the daily rhythms of hypothalamic expression of genes involved in the photoperiodic regulation of annual cycles in birds. We measured the 4-hourly mRNA expression of genes involved in the photoperiodic transduction (OPN5, EYA3, CGA, TSHβ, DIO2, DIO3) and neurosteroid-dependent processes (AR, CYP19, ERα, ERβ) in the hypothalamus of migratory blackheaded buntings photoinduced with photosensitive, photostimulated (early and late stimulated) and photorefractory seasonal states. There were significant differences in daily mRNA profiles between the photoperiodic states. Particularly, increased CGA, TSHβ and DIO2 and decreased DIO3 mRNA levels in the early photostimulated state, compared to the photosensitive state, suggest that thyroid hormones have a role in photostimulation in buntings. Similar differences in the expression of genes coding for the aromatase enzyme (CYP19) and receptors for oestrogen (ERα, ERβ) (but not androgen; AR) indicate that there is seasonal alteration in the neuro-oestrogen-mediated functions. Furthermore, peak expression times of CGA, TSHβ and DIO2 genes at hours 14-15 of the day in the early stimulated state indicated molecular regulation of the daily rhythm of photoinducibility in buntings. Most significantly, however, we found an attenuated daily rhythm in thyroid hormone modulatory genes and a switch of peak expression time from day to night in CYP19 mRNA rhythm in the subsequent late photostimulated state, although testicular maturation still persisted. These alterations in daily rhythms may have signalled the initiation of processes underlying other seasonal phenologies in parallel with the gonadal response, such as a manifestation of the night-time flight in buntings. These results show alterations in daily rhythms underlying the transcriptional regulation of the photoperiod-induced seasonal states in migratory blackheaded buntings.

Hypothalamic and liver transcriptome from two crucial life‐history stages in a migratory songbird

“…In LD, birds exhibit fat deposition and weight gain, Zugunruhe (migratory restlessness; intense nocturnal activity and wing whirring in captive birds), and show elevated circulating concentrations of metabolites (e.g. glucose, triglycerides) and metabolic hormones, such as insulin and corticosterone (Agatsuma & Ramenofsky, ; Bairlein, ; Bartell & Gwinner, ; Fuchs, Haney, Jechura, Moore, & Bingman, ; Gwinner & Czeschlik, ; Mishra, Singh, & Kumar, ; Rani, Malik, Trivedi, Singh, & Kumar, ; Trivedi, Kumar, Rani, & Kumar, ).…”

“…birds fatten and gain weight, develop nocturnal Zugunruhe and show elevated plasma corticosterone, testosterone and luteinizing hormone (LH) concentrations and gonadal recrudescence (Jain & Kumar, 1995;Mishra et al, 2017;Misra et al, 2004;Rani et al, 2006). Hypothalamus and liver mRNA levels of the circadian clock and light-and thyroid hormone-responsive genes and of genes involved in carbohydrate and fat metabolism and oxidative phosphorylation show changes with alteration in the seasonal state (Mishra et al, 2017;Singh et al, 2015;Trivedi et al, 2014;Trivedi, Malik, Rani, & Kumar, 2015). We predicted transcriptome-wide changes in the hypothalamus and liver with photostimulation of the spring migratory state in black-headed buntings.…”

Transcriptome‐wide changes in testes reveal molecular differences in photoperiod‐induced seasonal reproductive life‐history states in migratory songbirds

“…We interpret this as a difference in the activation of apoptotic pathways, perhaps by p53 dependent cellular apoptosis (Jackson, Cho, Stein, & Liang, ), during LD‐induced states. Perhaps, there is the concurrent activation, albeit at different rates, of the molecular processes underlying the testicular maturation and the onset of photorefractoriness in buntings, as suggested by previous studies in other photoperiodic songbirds including canaries ( Serinus canarius ; Storey & Nicholls, ), European starlings ( Sturnus vulgaris ; Dawson, ) and redheaded buntings (Mishra, Bhardwaj, Malik, & Kumar, ). It is suggested that the exposure to a stimulatory photoperiod initiates concurrently the testicular maturation and development of refractoriness but at different rates: photostimulation of the testicular maturation is overridden by that of the development of photorefractoriness by a week of exposure to long days (Nicholls, Goldsmith, & Dawson, ; Storey & Nicholls, ).…”

“…All procedures were approved by the Institutional Animal Ethics Committee of the Department of Zoology, University of Lucknow (protocol no: LU/ZOOL/IRPHA/Protocol2.3/NOV07), where the experiment was done. We used testes from the experiment, as earlier described (Mishra, Singh, & Kumar, ; D. Singh, Trivedi, Rani, Panda, & Kumar, ). Briefly, adult male black‐headed buntings were maintained until the beginning (for about 40 weeks) of the experiment under short days (SD; 8L:16D, winter‐like photoperiod) in which they were unstimulated and photosensitive SDSE, or exposed to long days (LD, 16L:8D, summer‐like photoperiod) in which following testicular maturation cycle they were photorefractory, LDRF (similar to post‐breeding condition; D. Singh et al, ).…”

“…Thereafter, gene‐specific primers (Table ) were used for measurement of mRNA expression using SYBR green chemistry on Applied Biosystems StepOne Plus thermal cycler (Applied Biosystems, Foster City, CA). Both target and reference genes ( β‐actin ) were run in duplicates and relative mRNA expression levels were calculated by method (Livak & Schmittgen, ) as routinely done in our laboratory (Mishra, Singh, et al, Mishra, Bharadhwaj, et al, ; D. Singh et al, ). We first calculated Δ C t value as a difference between the threshold cycles ( C t ) of target and reference gene ( C t [target] − C t [reference] ).…”