Effects of photoperiod extension on clock gene and neuropeptide RNA expression in the SCN of the Soay sheep

In mammals, changing daylength (photoperiod) is the main synchronizer of seasonal functions. The photoperiodic information is transmitted through the retino-hypothalamic tract to the suprachiasmatic nuclei (SCN), site of the master circadian clock. To investigate effects of day length change on the sheep SCN, we used in-situ hybridization to assess the daily temporal organization of expression of circadian clock genes (Per1, Per2, Bmal1 and Fbxl21) and neuropeptides (Vip, Grp and Avp) in animals acclimated to a short photoperiod (SP; 8h of light) and at 3 or 15 days following transfer to a long photoperiod (LP3, LP15, respectively; 16h of light), achieved by an acute 8-h delay of lights off. We found that waveforms of SCN gene expression conformed to those previously seen in LP acclimated animals within 3 days of transfer to LP. Mean levels of expression for Per1-2 and Fbxl21 were nearly 2-fold higher in the LP15 than in the SP group. The expression of Vip was arrhythmic and unaffected by photoperiod, while, in contrast to rodents, Grp expression was not detectable within the sheep SCN. Expression of the circadian output gene Avp cycled robustly in all photoperiod groups with no detectable change in phasing. Overall these data suggest that synchronizing effects of light on SCN circadian organisation proceed similarly in ungulates and in rodents, despite differences in neuropeptide gene expression

Anti-angiogenic VEGFAxxxb transcripts are not expressed in the medio-basal hypothalamus of the seasonal sheep

Source at https://doi.org/10.1371/journal.pone.0197123.This study investigated Vegfa expression in the pars tuberalis (PT) of the pituitary and medio-basal hypothalamus (MBH) of sheep, across seasons and reproductive states. It has recently been proposed that season impacts alternative splicing of Vegfa mRNA in the PT, which shifts the balance between angiogenic VEGFAxxx and anti-angiogenic VEGFAxxxb isoforms (with xxx the number of amino acids of the mature VEGFA proteins) to modulate seasonal breeding. Here, we used various RT-PCR methodologies and analysis of RNAseq datasets to investigate seasonal variation in expression and splicing of the ovine Vegfa gene. Collectively, we identify 5 different transcripts for Vegfa within the ewe PT/MBH, which correspond to splicing events previously described in mouse and human. All identified transcripts encode angiogenic VEGFAxxx isoforms, with no evidence for alternative splicing within exon 8. These findings led us to investigate in detail how “Vegfaxxxb-like” PCR products could be generated by RT-PCR and misidentified as endogenous transcripts, in sheep and human HEK293 cells. In conclusion, our findings do not support the existence of anti-angiogenic VEGFAxxxb isoforms in the ovine PT/MBH and shed new light on the interpretation of prior studies, which claimed to identify Vegfaxxxb isoforms by RT-PCR

Discontinuity in the molecular neuroendocrine response to increasing daylengths in Ile-de-France ewes: Is transient Dio2 induction a key feature of circannual timing?

This is the peer reviewed version of the following article: Dardente, H., Lomet, D., Chesneau, D., Pellicer-Rubio, M.-T. & Hazlerigg, D. (2019). Discontinuity in the molecular neuroendocrine response to increasing daylengths in Ile‐de‐France ewes: Is transient Dio2 induction a key feature of circannual timing? Journal of Neuroendocrinology, 31(8), e 12775, which has been published in final form at https://doi.org/10.1111/jne.12775. . This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.In mammals, melatonin is responsible for the synchronisation of seasonal cycles to the solar year. Melatonin is secreted by the pineal gland with a profile reflecting the duration of the night and acts via the pituitary pars tuberalis (PT), which in turn modulates hypothalamic thyroid hormone status via seasonal changes in the production of locally‐acting thyrotrophin. Recently, we demonstrated that, in the Soay sheep, photoperiodic induction of Tshb expression and consequent downstream hypothalamic changes occur over a narrow range of photoperiods between 12 and 14 hours in duration. In the present study, we aimed to extend our molecular characterisation of this pathway, based on transcriptomic analysis of photoperiodic changes in the pituitary and hypothalamus of ovariectomised, oestradiol‐implanted Ile‐de‐France ewes. We demonstrate that photoperiodic treatments applied before the winter solstice elicit two distinctive modes of accelerated reproductive switch off compared to ewes held on a simulated natural photoperiod, with shut‐down occurring markedly faster on photoperiods of 13 hours or more than on photoperiods of 12 hours and less. This pattern of response was reflected in gene expression profiles of photoperiodically sensitive markers, both in the PT (Tshb, Fam150b, Vmo1, Ezh2 and Suv39H2) and in tanycytes (Tmem252 and Dct). Unexpectedly, the expression of Dio2 in tanycytes did not show any noticeable increase in expression with lengthening photoperiods. Finally, the expression of Kiss1, the key activator of gonadotrophin‐releasing hormone release, was proportionately decreased by lengthening photoperiods, in a pattern that correlated strongly with gonadotrophin suppression. These data show that stepwise increases in photoperiod lead to graded molecular responses at the level of the PT, a progressive suppression of Kiss1 in the hypothalamic arcuate nucleus and luteinising hormone/follicle‐stimulating hormone release by the pituitary, despite apparently unchanged Dio2 expression in tanycytes. We hypothesise that this apparent discontinuity in the seasonal neuroendocrine response illustrates the transient nature of the thyroid hormone‐mediated response to long days in the control of circannual timing

Ancestral TSH mechanism signals summer in a photoperiodic mammal

SummaryIn mammals, day-length-sensitive (photoperiodic) seasonal breeding cycles depend on the pineal hormone melatonin, which modulates secretion of reproductive hormones by the anterior pituitary gland [1]. It is thought that melatonin acts in the hypothalamus to control reproduction through the release of neurosecretory signals into the pituitary portal blood supply, where they act on pituitary endocrine cells [2]. Contrastingly, we show here that during the reproductive response of Soay sheep exposed to summer day lengths, the reverse applies: Melatonin acts directly on anterior-pituitary cells, and these then relay the photoperiodic message back into the hypothalamus to control neuroendocrine output. The switch to long days causes melatonin-responsive cells in the pars tuberalis (PT) of the anterior pituitary to increase production of thyrotrophin (TSH). This acts locally on TSH-receptor-expressing cells in the adjacent mediobasal hypothalamus, leading to increased expression of type II thyroid hormone deiodinase (DIO2). DIO2 initiates the summer response by increasing hypothalamic tri-iodothyronine (T3) levels. These data and recent findings in quail [3] indicate that the TSH-expressing cells of the PT play an ancestral role in seasonal reproductive control in vertebrates. In mammals this provides the missing link between the pineal melatonin signal and thyroid-dependent seasonal biology

Assaisonnement au VEGFxxxb anti-angiogénique pour votre mouton ? Non, merci.

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Scientific English Writing. How to conceive, write and publish papers that get cited

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Bases moléculaires des rythmes biologiques

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Habilitation à Diriger des Recherches

Diplôme : HD

Calendar cells and circannual cycle

Calendar cells and circannual cycle. COST action BM110