Biology subjects

Fontaine, R.

Publications and source records attributed to Fontaine, R..

13 recordsLinked to original sources

bioRxiv2025

Shivering, but not adipose tissue thermogenesis, increases as a function of mean skin temperature in cold-exposed men and women

Skin cooling results in the activation of heat generating mechanisms to counteract heat lost to the environment. Here, we aim to understand the extent that variations in cold-stimulated heat production may be driven by differences in the contribution of shivering and non-shivering thermogenesis (NST) and the interaction with biological sex. Using a novel mean skin temperature clamping technique in healthy men and women, our data shows that cold-stimulated heat production rises with increasing shivering and myocardial oxidative metabolism in a skin temperature-dependent fashion. Shivering and myocardial thermogenesis were also moderately associated. In contrast, adipose tissue NST did not increase in a linear manner to reductions in skin temperature. Men and women displayed similar thermoregulatory responses, although women presented more pronounced shivering through a greater recruitment of lower-body muscles and greater number of motor units recruited. Thus, shivering contributes proportionally to cold-induced thermogenesis whereas adipose tissue thermogenesis displays an all-or-none response.

physiology↗

bioRxiv2025

Photoperiod decoder 1 regulates seasonal changes in energy metabolism through the growth hormone signaling pathway

Seasonal changes in metabolism are crucial for animals to adapt to annual environmental fluctuations. However, the molecular mechanisms underlying these adaptations remain poorly understood. Here, we identified a novel gene, photoperiod decoder 1 (phod1), which exhibits a unique bimodal expression pattern under long-day conditions in Japanese medaka fish (Oryzias latipes). While phod1 is conserved across many vertebrates, except for eutherians, its function remained unknown. Single-cell RNA sequencing analysis revealed that phod1 is predominantly expressed in specific pituitary cells that co-express opsin and circadian clock genes. Transcriptomic analysis using phod1 knockout fish demonstrated that phod1 is essential for photoperiodic regulation of growth hormone. Furthermore, transcriptomic and metabolomic analyses of the liver, the primary target of growth hormone, revealed significant alterations in energy metabolism. Behavioral analysis also showed that phod1 knockout fish exhibited significantly reduced locomotor activity. These findings indicate that phod1 plays a crucial role in seasonal metabolic adaptation through modulation of the growth hormone signaling pathway.

physiology↗

bioRxiv2024

Additions to the list of arthropods of Reunion Island

Contribution to the inventory of arthropods of Reunion Island This work is a synthesis of new taxa for the Reunion Island identified between 1963 and 2022 and not published to date. The collections were carried out mainly by researchers and technicians from CIRAD or FDGDON. Sampling mainly targeted at crop pests and their natural enemies. The list includes 101 taxa new for Reunion. The Hymenoptera and Hemiptera are the most represented orders.

zoology↗

bioRxiv2023

Photoperiod regulates gonadotrope cell division in medaka via melatonin, Tsh and folliculostellate cells

In vertebrates, pituitary gonadotropins (follicle-stimulating and luteinizing hormones: FSH and LH) regulate gonadal development and maturation, therefore playing an essential role in reproduction. The seasonal regulation of gonadotropins has been widely studied in mammals and birds, and in these taxa thyroid-stimulating hormone (TSH) was found to play a critical role. By contrast, the seasonal regulation of gonadotropins remains unclear in teleost fish. In addition, the seasonal regulation of gonadotrope (gonadotropin-producing cell) proliferation has not been elucidated in any vertebrate group. Using the teleost fish medaka as a model, we show for the first time that long photoperiod enables reproduction by stimulating gonadotropin mRNA synthesis and gonadotrope cell proliferation. In female medaka, this proliferation is achieved by gonadotrope mitosis. We then demonstrate that in female medaka, photoperiod stimulates gonadotropin mRNA production and mitosis via an indirect intra-pituitary pathway, involving pituitary Tsh cells. We show that non-endocrine folliculostellate cells in the pituitary mediate the Tsh signal regulating gonadotrope activity and proliferation, as they are the only pituitary cells to express Tsh receptors and send projections to gonadotropes. Finally, we show that melatonin suppresses pituitary tshba expression in fish exposed to long photoperiod, suggesting that short photoperiod inhibits gonadotropin synthesis via melatonin in both fish and mammals. This study therefore demonstrates that in fish, photoperiod regulates gonadotrope cell activity and mitosis via a melatonin-Tsh pathway. It also reveals the existence of a novel intra-pituitary pathway for seasonal regulation of gonadotropes, involving folliculostellate cells, which we propose might also exist in other vertebrates. SIGNIFICANCEIn seasonally breeding mammals and birds, the production of the hormones that regulate reproduction (gonadotropins) by gonadotropes is controlled by the pituitary thyroid-stimulating hormone (TSH) through an indirect pathway via the brain. However, in fish, how seasonal environmental signals influence gonadotropins remains unclear. Here, we show that in a long day seasonally breeding fish, medaka, photoperiod not only regulates the activity (hormone production) of the gonadotropes but also their proliferation. We also reveal a novel intra-pituitary pathway that regulates gonadotrope cell activity and number. This pathway involves melatonin, Tsh, and folliculostellate cells. Interestingly, as all these components are also found in the mammalian pituitary, this study suggests the existence of an alternative regulatory mechanism of seasonal gonadotropin production across vertebrates.

neuroscience↗

bioRxiv2023

Impact of light pollution at night on male reproductive success in Japanese medaka (Oryzias latipes)

Environmental light is perceived and anticipated by organisms to synchronize their biological cycles. Therefore, exposure to artificial light at night could disrupt diurnal and seasonal rhythmicity. Reproduction is a complex physiological process involving integration of environmental signals by the brain, and release of endocrine signals by the pituitary that regulate gametogenesis and spawning. In addition, males from many species form a dominance hierarchy that, through a combination of aggressive and protective behavior, influences their reproductive success. In this study, we investigated the effect of different light regimes, including light pollution at night and continuous light, on the fitness of male fish within a dominance hierarchy using a model fish, the Japanese medaka. In normal light/dark rhythm conditions, we observed that dominant males are more aggressive, remain closer to the female, and spend ten-fold more time spawning than subordinates. By using males with different genotypes, we determined the paternity of the progeny and found that even though subordinate males spend less time with the females, they are equally successful at fertilizing eggs in normal light conditions due to an efficient sneaking behavior. However, when exposed to light at night, dominant males fertilize more eggs. We indeed found that when exposed to nocturnal light pollution, dominant males produce higher quality sperm than subordinate males. Surprisingly, we did not find differences in circulating sex steroid levels, pituitary gonadotropin levels, or gonadosomatic index between dominant and subordinate males, neither in control nor night light condition. Continuous light was found to completely inhibit establishment of male hierarchy. This study is the first to report an effect of light pollution on sperm quality with an impact on male fertilization success in any vertebrate. It has broad implications for fish ecology in urban areas with potential impacts on the genetic diversity of these fish populations. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=95 SRC="FIGDIR/small/536935v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@149072dorg.highwire.dtl.DTLVardef@1763cd7org.highwire.dtl.DTLVardef@194586aorg.highwire.dtl.DTLVardef@38c518_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIIn a triadic relationship, subordinate medaka show sneaking behavior during female spawning, allowing them to produce about 50% of the offspring. C_LIO_LIContinuous light inhibits establishment of male hierarchy. C_LIO_LILight pollution at night shifts the balance of reproductive efficiency between dominant and subordinate males, benefiting dominant males. C_LIO_LIExposure to light pollution at night improves sperm quality in dominant fish relative to subordinates, but does not clearly affect reproductive hormone levels. C_LI

zoology↗

bioRxiv2022

Sexually dimorphic regulation of gonadotrope cell hyperplasia in medaka pituitary via mitosis and transdifferentiation

The two pituitary gonadotropins, Fsh and Lh, regulate the reproductive function in vertebrates. While many studies have investigated the regulation of gonadotropin production and release by the sex steroid feedback, its role on the regulation of gonadotrope cell number remains unclear. Using medaka as a model and an optimized protocol to restore physiological sex steroids levels following gonadectomy, we show that gonadal sex steroids not only decrease fshb transcript levels, but also Fsh cell number in both sexes. We then investigated the origin of the Fsh cell hyperplasia induced by gonadectomy. In both sexes, BrdU incubation shows that this is achieved via Fsh cell mitosis. In situ hybridization reveals that new Fsh cells also originate from transdifferentiating Tsh cells in females, but not in males. Both phenomena are inhibited by sex steroid supplementation via feeding. In males (but not females), gonadectomy (without recovery with sex steroid supplementation) also reduces sox2 transcript levels and Sox2-immunopositive population volume, suggesting that sox2-progenitors may be recruited to produce new Fsh cells. Opposite to Fsh cells, gonadectomy decreases lhb levels in both sexes, and levels are not restored by sex steroid supplementation. In addition, the regulation of Lh cell number also seems to be sex dependent. Removal of gonadal sex steroids stimulates Lh cell mitosis in male (like Fsh cells), but not in females. To conclude, our study provides the first evidence on sexually dimorphic mechanisms used in the fish pituitary to remodel gonadotrope populations in response to sex steroids. HIGHLIGHTS- Supplementing gonadectomized fish with sex steroids via feeding allows for the recovery of physiological circulating levels of sex steroids. - Gonadal sex steroids not only regulate gonadotrope cell activity, but also gonadotrope cell number. - Removal of gonadal sex steroids induces Fsh cell hyperplasia via mitosis of Fsh cells in both sexes, and transdifferentiation of Tsh cells into bi-hormonal Tsh/Fsh cells in females only. - Gonadectomy also reduces the number of Sox2 progenitor cells in males (but not in females), suggesting that they may be recruited to contribute to Fsh cell hyperplasia. - Removal of gonadal sex steroids stimulates Lh cell mitosis in males, but not in females.

neuroscience↗

bioRxiv2022

Sperm collection and computer-assisted sperm analysis in the teleost model Japanese medaka (Oryzias latipes)

Japanese medaka (Oryzias latipes) are a teleost fish and an emerging vertebrate model for ecotoxicology, developmental, genetics, and physiology research. Medaka are also used extensively to investigate vertebrate reproduction, which is an essential biological function as it allows a species to perpetuate. Sperm quality is an important indicator of male fertility and thus reproduction success. Techniques for extracting sperm and sperm analysis are well documented for many species, including for teleost fish. Collecting semen is relatively simple in larger fish but can be more complicated in small model fish as they produce less sperm and are more delicate. This article therefore describes two methods of sperm collection in the small model fish Japanese medaka: testes dissection and abdominal massage. We demonstrate that both approaches are viable for medaka and show that abdominal massage can be performed a repeated number of times as the fish quickly recover from the procedure. We also describe a protocol for computer-assisted sperm analysis in medaka to objectively assess several important indicators of medaka sperm quality (motility, progressivity, duration of motility, relative concentration). The use of these procedures combined with the other advantages of using this small teleost model will greatly improve the understanding of the environmental, physiological, and genetic factors influencing fertility in vertebrate males. SUMMARYThis article describes two quick and efficient methods to collect semen from the small model fish medaka (Oryzias latipes), as well as a protocol to reliably assess sperm quality using computer-assisted sperm analysis (CASA).

physiology↗

bioRxiv2021

Ectopic expression of lipid homeostasis genes in rare cells of the teleost pituitary gland

Directing both organismal homeostasis and physiological adaptation, the pituitary is a key endocrine gland in all vertebrates. It communicates the needs of the organism to different organs by secreting hormones into the bloodstream. Here, we have used the model fish medaka to investigate the developmental dynamics in the pituitary using a comprehensive RNA-seq time series. By linking developmental expression trends to single-cell RNA-seq profiles, we show how the transcriptional activities of cell types change during sexual maturation. One of the most prominent changes is the decline of the non-endocrine folliculo-stellate cell populations, and especially of rare cells expressing genes encoding secreted lipid transport proteins. As these genes are typically associated with the liver, this reveals the existence of unexpected connections between endocrine communication, lipid homeostasis, and sexual maturation.

physiology↗

bioRxiv2021

Sexual maturation in Atlantic salmon male parr may be triggered both in early spring and late summer under standard farming conditions

Male Atlantic salmon (Salmo salar) display different sexual strategies, maturing either as parr during the freshwater phase (as sneaky spawners), or as post smolts following one or several years at sea. First sexual maturation (puberty) occurs at different times depending on environmental and genetic factors. To improve our knowledge on the timing (age and season) of first sexual maturation in Atlantic salmon male parr, we investigated pubertal activation in second generation farmed salmon from the Norwegian river Figgjo, reared under natural conditions of photoperiod and water temperature. Histological analysis, in combination with morphometric measurements, plasma androgen levels and pituitary gonadotropin gene expression analysis revealed that, as previously reported, some male parr initiated early sexual maturation in spring at one year of age. Interestingly, some male parr were observed to initiate sexual maturation already in autumn, six months after hatching (under-yearlings), much earlier than reported in previous studies. One-year old maturing males showed a low induction in gonadotropin levels, while under-yearling maturing males displayed a significant increase in fshb transcripts as compared to immature fish. Plasma testosterone, detectable also in immature males, increased constantly during testes development, while 11-ketotestosterone, undetectable in immature and early maturing males, increased during more advanced stages of maturation. A mild feminization of the testes (ovotestes) was detected in a subset of samples. This study brings new knowledge on the little investigated field of sexually maturing under-yearlings in Atlantic salmon. This is also the first study comparing the physiology of under-yearling vs one-year old maturing male parr, thus bringing new insights to the remarkable plasticity of Atlantic salmon puberty.

physiology↗

bioRxiv2020

Characterization of hormone-producing cell types in the teleost pituitary gland using single-cell RNA-seq

The pituitary is the vertebrate endocrine gland responsible for the production and secretion of several essential peptide hormones. These, in turn, control many aspects of an animals physiology and development, including growth, reproduction, homeostasis, metabolism and stress responses. In teleost fish, each hormone is presumably produced by a specific cell type. However, key details on the regulation of, and communication between these cell types remain to be resolved. We have therefore used single-cell sequencing to generate gene expression profiles for 2592 and 3804 individual cells from the pituitaries of female and male adult medaka (Oryzias latipes), respectively. Based on expression profile clustering, we define 15 and 16 distinct cell types in the female and male pituitary, respectively, of which ten are involved in the production of a single peptide hormone. Collectively, our data provide a high-quality reference for studies on pituitary biology and the regulation of hormone production, both in fish and in vertebrates in general.

physiology↗

bioRxiv2019

Gonadotropes in medaka grow long extensions with varicosity-like swellings, projecting towards each other and blood vessels.

Accumulating evidence in the scientific literature indicates that some pituitary cell types are organized in complex networks. Previous observations have indicated that this may also be the case in medaka (Oryzias latipes), where long cellular extensions with varicosity-like swellings are formed by luteinizing hormone (Lh)-producing gonadotropes expressing green fluorescent protein. In this study, immunofluorescence of intact pituitaries reveal that Lh beta polypeptides are mainly located in the varicosity-like swellings and at the extremity of the extensions. Some extensions approach nearby Lh-producing cells, and other extensions are in close contact with blood vessels. To investigate whether these extensions may contribute to network formation, we followed their development using confocal and fluorescent microscopy on primary cultures. During the first two days in culture, the extensions initiated the formation of homotypic cellular networks and clustering. The extensions were classified as either major or minor. Major extensions were several cell diameters long, dependent on microtubules, and displaying varicosity-like swellings at regular intervals. Minor extensions typically protruded from the major, were significantly shorter and thinner, and dependent on actin. The swellings were dependent on both microtubules and actin. Flash photolysis of caged Ca2+ showed that the signal was propagated along the major extensions, intensifying in each swelling, indicating a continuous structure. However, the Ca2+ signal did not transfer to the next cell in the network, but was transferred between cells merged at their somas. In summary, Lh-producing gonadotropes in medaka display a complex cellular structure of extensions, possibly linked to communication with blood vessels and/or other gonadotrope cells.

cell biology↗

bioRxiv2019

Gnrh1-induced responses are indirect in female medaka Fsh cells

Reproductive function in vertebrates is stimulated by gonadotropin-releasing hormone (GnRH) that controls the synthesis and release of the two pituitary gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH and LH, which regulates different stages of gonadal development, are produced by two different cell types in the fish pituitary, in contrast to mammals and birds, thus allowing the investigation of their differential regulation. In the present work, we show by fluorescent in situ hybridization that Lh cells in adult female medaka express Gnrh receptors, whereas Fsh cells do not. This is confirmed by patch clamp recordings and cytosolic Ca2+ measurements on dispersed pituitary cells, where Lh cells, but not Fsh cells, respond to Gnrh1 by increased action potential frequencies and cytosolic Ca2+ levels. In contrast, both Fsh and Lh cells are able to respond electrically and by elevating the cytosolic Ca2+ levels to Gnrh1 in brain-pituitary tissue slices. Using Ca2+ uncaging in combination with patch clamp recordings and cytosolic Ca2+ measurements, we show that Fsh and Lh cells form homo- and heterotypic networks in the pituitary. Taken together, these results show that the effects of Gnrh1 on Fsh release in adult female medaka is indirect, likely mediated via Lh cells.

physiology↗

bioRxiv2019

Plasticity in medaka gonadotropes via cell proliferation and phenotypic conversion

Follicle stimulating hormone (Fsh) and luteinizing hormone (Lh) produced by the gonadotropes, play a major role in control of reproduction. Contrary to mammals and birds, Lh and Fsh are mostly produced by two separate cell types in teleost. Here, we investigated gonadotrope plasticity, using transgenic lines of medaka (Oryzias latipes) where DsRed2 and hrGfpII are under the control of fshb and lhb promotors respectively. We found that Fsh cells first appear in the pituitary at 8 dpf. Similar to in Lh cells, Fsh cells show hyperplasia from juvenile to adult stages. Hyperplasia is stimulated by estradiol exposure. Both Fsh and Lh cells show hypertrophy during puberty with similar morphology. They also share similar behavior, using their cellular extensions to make networks. We observed bi-hormonal gonadotropes in juvenile and adult fish but not during larval stage where only mono-hormonal cells are observed, suggesting the existence of phenotypic conversion between Fsh and Lh in later stages. This is demonstrated in cell culture, where some Fsh start to produce lhb, a phenomenon enhanced by gonadotropin releasing hormone (Gnrh) stimulation. We have previously shown that medaka Fsh cells lack Gnrh receptors, but here we show that with time in culture, some Fsh cells start responding to Gnrh, while fshb mRNA levels are significantly reduced, both suggestive of phenotypic change. All together, these results reveal high plasticity of gonadotropes due to both estradiol sensitive proliferation and Gnrh promoted phenotypic conversion, and also shows that gonadotropes lose part of their identity when kept in cell culture.

physiology↗