Yolk Corticosterone Research Articles

Nutritional and physiological responses to dietary phosphorus levels and phytase in pullets and laying hens

The objective of this study was to determine the effects of dietary available phosphorus (P) levels and dietary phytase added into the very low-P diet on the performance, mineral balance, odor emission, and stress responses in growing pullets and laying hens during 13 to 32 wk of age. One hundred sixty-eight pullets (Hy-Line Brown) were randomly assigned into 1 of 4 dietary treatments with 7 replicates of 6 birds each. Experimental diets were formulated to contain 3 graded P levels at 0.25, 0.35, and 0.45% during 13 to 15 wk (phase 1), 0.25, 0.35, and 0.45% during 16 to 18 wk (phase 2), and 0.20, 0.30, and 0.40% during 19 to 32 wk (phase 3). In addition, dietary phytase (500 FTU/kg matrix values) was added into the very low-P diets (0.20% during 13-15 wk, 0.25% during 16-18 wk, and 0.20% during 19-32 wk) to meet the nutritional adequacy with standard P diets. In all phases, decreasing dietary P levels did not affect (P > 0.05) growth, laying performance, and egg qualities. Decreasing dietary P levels linearly increased the relative duodenal and oviduct weights (P < 0.05), and quadratically increased the relative ovary weight in pullets (P = 0.016). Dietary phytase lowered (P = 0.021) the relative duodenal weight compared with the very low-P diet. Tibia breaking strength and tibia Mg contents in pullets were linearly lowered (P < 0.05) as dietary P levels decreased. Dietary phytase tended to increase (P = 0.091) tibia breaking strength and significantly increased (P = 0.025) tibia Mg content compared with the very low-P diet. Dietary P levels and dietary phytase affected (P < 0.05) ileal crypt depth and ileal villus height: crypt depth ratio in pullets. Decreasing dietary P levels linearly decreased (P < 0.01) crude fat digestibility and P excretion in both pullets and laying hens. Dietary phytase reversed (P < 0.05) the very low-P diet-mediated decrease of crude fat digestibility in pullets and laying hens. Dietary P levels and dietary phytase affected (P < 0.05) odor emission including ammonia in pullets and total volatile fatty acids in laying hens. Finally, lowering dietary P levels increased (P < 0.01) yolk corticosterone concentrations and the increased corticosterone concentration by the very low-P diet was reversed by dietary phytase. Collectively, our study shows that decreasing dietary P levels induced nutritional and physiological responses in pullets and laying hens and these P-mediated negative effects were mitigated by dietary phytase.

Interplay of cooperative breeding and predation risk on egg allocation and reproductive output.

Predation risk can influence behavior, reproductive investment, and, ultimately, individuals' fitness. In high-risk environments, females often reduce allocation to reproduction, which can affect offspring phenotype and breeding success. In cooperative breeders, helpers contribute to feed the offspring, and groups often live and forage together. Helpers can, therefore, improve reproductive success, but also influence breeders' condition, stress levels and predation risk. Yet, whether helper presence can buffer the effects of predation risk on maternal reproductive allocation remains unstudied. Here, we used the cooperatively breeding sociable weaver Philetairus socius to test the interactive effects of predation risk and breeding group size on maternal allocation to clutch size, egg mass, yolk mass, and yolk corticosterone. We increased perceived predation risk before egg laying using playbacks of the adults' main predator, gabar goshawk (Micronisus gabar). We also tested the interactive effects of group size and prenatal predator playbacks on offspring hatching and fledging probability. Predator-exposed females laid eggs with 4% lighter yolks, but predator-calls' exposure did not clearly affect clutch size, egg mass, or egg corticosterone levels. Playback-treatment effects on yolk mass were independent of group size, suggesting that helpers' presence did not mitigate predation risk effects on maternal allocation. Although predator-induced reductions in yolk mass may decrease nutrient availability to offspring, potentially affecting their survival, playback-treatment effects on hatching and fledging success were not evident. The interplay between helper presence and predator effects on maternal reproductive investment is still an overlooked area of life history and physiological evolutionary trade-offs that requires further studies.

Maternally derived avian corticosterone affects offspring genome-wide DNA methylation in a passerine species.

Avian embryos develop in an egg composition which reflects both maternal condition and the recent environment of their mother. In birds, yolk corticosterone (CORT) influences development by impacting pre- and postnatal growth, as well as nestling stress responses and development. One possible mechanism through which maternal CORT may affect offspring development is via changes to offspring DNA methylation. We sought to investigate this, for the first time in birds, by quantifying the impact of manipulations to maternal CORT on offspring DNA methylation. We non-invasively manipulated plasma CORT concentrations of egg-laying female zebra finches (Taeniopygia castanotis) with an acute dose of CORT administered around the time of ovulation and collected their eggs. We then assessed DNA methylation in the resulting embryonic tissue and in their associated vitelline membrane blood vessels, during early development (5 days after lay), using two established methods - liquid chromatography-mass spectrometry (LC-MS) and methylation-sensitive amplification fragment length polymorphism (MS-AFLP). LC-MS analysis showed that global DNA methylation was lower in embryos from CORT-treated mothers, compared to control embryos. In contrast, blood vessel DNA from eggs from CORT-treated mothers showed global methylation increases, compared to control samples. There was a higher proportion of global DNA methylation in the embryonic DNA of second clutches, compared to first clutches. Locus-specific analyses using MS-AFLP did not reveal a treatment effect. Our results indicate that an acute elevation of maternal CORT around ovulation impacts DNA methylation patterns in their offspring. This could provide a mechanistic understanding of how a mother's experience can affect her offspring's phenotype.

First person – Emily Harders

ABSTRACT First Person is a series of interviews with the first authors of a selection of papers published in Biology Open, helping researchers promote themselves alongside their papers. Emily Harders is first author on ‘ Avian extraembryonic membranes respond to yolk corticosterone early in development’, published in BiO. Emily conducted the research described in this article while a master's student in Dr Ryan Paitz's lab at Illinois State University, Normal, USA. She is now currently a specimen processing technician at Nebraska Medicine in Omaha, Nebraska, while she applies for PhD programs. She is interested in understanding how maternal/fetal signalling is regulated in extraembryonic tissues.

Avian extraembryonic membranes respond to yolk corticosterone early in development.

During times of maternal stress, developing embryos can be exposed to elevated levels of glucocorticoids, which can affect development and permanently alter offspring phenotype. In placental species, the placenta mediates fetal exposure to maternal glucocorticoids via metabolism, yet the placenta itself responds to glucocorticoids to regulate offspring growth and development. In oviparous species, maternal glucocorticoids can be deposited into the egg yolk and are metabolized early in development. This metabolism is mediated by the extraembryonic membranes, but it is unknown if the extraembryonic membranes also respond to maternal glucocorticoids in a way comparable to the placenta. In this study, we quantified the expression of acyl-CoA thioesterase 13 (Acot13) as an initial marker of the membrane's response to corticosterone in chicken (Gallus gallus) eggs. Acot13 regulates fatty acid processing in the embryo, to potentially regulate resource availability during development. We addressed the following questions using Acot13 expression: 1) Do the extraembryonic membranes respond to yolk corticosterone early in development? 2) Is the response to corticosterone dependent on the dose of corticosterone? 3) What is the duration of the response to corticosterone? 4) Does a metabolite of corticosterone (5β-corticosterone) elicit the same response as corticosterone? We found that corticosterone significantly induces the expression of Acot13 on day four of development and that expression of Acot13 increases with the dose of corticosterone. Further, we found expression of Acot13 is significantly elevated by corticosterone on days four and six of development compared to oil treated eggs, but not on days eight and ten. Although this response is transient, it occurs during a critical period of development and could initiate a cascade of events that ultimately alter offspring phenotype. Finally, we found that 5β-corticosterone does not increase the expression of Acot13, indicating that metabolism inactivates corticosterone. Ultimately, this study provides insight into the mechanisms underlying how maternally deposited glucocorticoids can affect embryonic development.

Extraembryonic metabolism of corticosterone protects against effects of exposure

When females experience stress during reproduction, developing embryos can be exposed to elevated levels of glucocorticoids, which can permanently affect offspring development, physiology, and behavior. However, the embryo can regulate exposure to glucocorticoids. In placental species, the placenta regulates embryonic exposure to maternal steroids via metabolism. In a comparable way, recent evidence has shown the extraembryonic membranes of avian species also regulate embryonic exposure to a number of maternal steroids deposited in the yolk via metabolism early in development. However, despite the known effects of embryonic exposure to glucocorticoids, it is not yet understood how glucocorticoids are metabolized early in development. To address this knowledge gap, we injected corticosterone into freshly laid chicken (Gallus gallus) eggs and identified corticosterone metabolites, located metabolomic enzyme transcript expression, tracked metabolomic enzyme transcript expression during the first six days of development, and determined the effect of corticosterone and metabolites on embryonic survival. We found that yolk corticosterone was metabolized before day four of development into two metabolites: 5β-corticosterone and 20β-corticosterone. The enzymes, AKR1D1 and CBR1 respectively, were expressed in the extraembryonic membranes. Expression was dynamic during early development, peaking on day two of development. Finally, we found that corticosterone exposure is lethal to the embryos, yet exposure to the metabolites is not, suggesting that metabolism protects the embryo. Ultimately, we show that the extraembryonic membranes of avian species actively regulate their endocrine environment very early in development.

The Effect of Low Temperature on Laying Performance and Physiological Stress Responses in Laying Hens.

The present study investigated the effect of low temperature on laying performance, egg quality, body temperature, yolk malondialdehyde, yolk corticosterone, and serum biochemistry in laying hens. A total of 40 laying hens (Hy-Line Brown) aged 36 weeks were housed in one of two environmental chambers kept at 12 ± 4.5 °C (low temperature) or 24 ± 3 °C (normal temperature) for 4 weeks. Low vs. normal temperature significantly increased (p < 0.05) live body weight, feed intake, and feed conversion ratio in laying hens. Skin surface temperature, but not rectal temperature, was decreased in laying hens exposed to low vs. normal temperature. Hens exposed to low temperature laid an intense eggshell color compared with those raised in a normal temperature. Malondialdehyde concentrations in yolk were increased in low-temperature-exposed laying hens compared with those at normal temperature conditions, but this effect was only noted on day 7, post the low-temperature exposure (p = 0.04). Finally, low vs. normal temperature increased the concentrations of total cholesterol and triglyceride in serum. Collectively, this study indicates that exposure to low temperature in laying hens initially disrupted antioxidant system and altered lipid metabolism in laying hens without inducing stress responses.

Yolk corticosterone and progesterone levels in Greater Rhea (Rhea americana) eggs vary in a changing social environment.

Maternal hormones in avian egg yolks may signal and prepare offspring for the prevailing conditions. However, this adjustment requires some degree of flexibility in regulating yolk hormone deposition. The Greater Rhea (Rhea americana) has a particular mating system that combines mixed polygyny and polyandry, communal nesting, and exclusive paternal care of chicks. In this species, we previously found that yolk hormone deposition varies among eggs of different captive populations and could influence chicks' physiology and behavior. However, it is still unknown whether females can modify yolk hormone deposition in a changing social environment. Using a captive population of Greater Rheas, in this study, we quantified yolk hormone levels before and after a reduction in the number of females present in the population. We found that females deposited on average higher yolk corticosterone and lower yolk progesterone after the change in their social environment. Since corticosterone deposited into the yolk comes exclusively from the female's plasma, our results suggest that females had, on average, higher plasma corticosterone levels. The change in the number of females may increase the events of male-male competitions, courtships, and matings, leading to an increase of corticosterone in the females' plasma and then into their eggs. Since we previously found that higher yolk corticosterone and lower yolk progesterone were associated with the production of chicks that have an attenuated stress response, the present study results suggest that yolk hormone deposition is mediated by flexible mechanisms that could adjust development to the prevailing conditions.

Comparison of stress biomarkers in laying hens raised under a long-term multiple stress condition

The objective of the current experiment was to compare various stress biomarkers including the heterophil to lymphocyte ratio (H:L ratio) in blood and the corticosterone (CORT) concentrations in feathers, claws, and egg yolk and to find the potential stress biomarkers in laying hens exposed to a long-term multiple stress condition. A total of 24 Hy-Line Brown laying hens at 47 wk of age were allotted to 2 distinct conditions including normal condition (NC) and multiple stress condition (MC) with 8 replicated cages. In NC treatment, 8 hens were raised individually in the cage (0.16 m2/hen) under the temperature of 21 ± 0.6°C. In MC treatment, 16 hens were raised with 2 hens per cage to decrease space allowance (0.08 m2/hen) and the temperature was maintained at 31 ± 1.6°C. The experiment lasted for 8 wk. The common diets and water were fed on an ad libitum basis during the experiment. Results indicated no interactions between stress conditions and duration of stress exposure for all measurements. Hens in MC treatment had a greater (P < 0.01) blood H:L ratio than those in NC treatment. The greater (P < 0.05) H:L ratio for MC treatment was observed at all weeks. Hens in MC treatment had greater (P < 0.05) feather CORT concentrations than those in NC treatment. Feather CORT concentrations were increased (P < 0.05) with duration of the experiment. However, stress conditions did not influence claw CORT concentrations. A tendency (P = 0.081) was observed for greater yolk CORT concentrations in MC treatment than in NC treatment. In conclusion, the H:L ratio in blood and CORT concentrations in feathers and egg yolks are considered potential stress biomarkers in laying hens exposed to stress conditions, although each measurement has its respective limitations. However, CORT concentrations in the claw appear to be insensitive to a long-term stress exposure.

Impact of relative humidity on the laying performance, egg quality, and physiological stress responses of laying hens exposed to high ambient temperature.

The present study investigated the effects of relative humidity (RH) on the laying performance, egg quality, and stress indicators of laying hens raised at high ambient temperatures. A total of 180 Hy-Line Brown laying hens (68-wk-old) were randomly allotted to one of the following three RH conditions for 12h a day (9:00 a.m.-9:00 p.m.) over four weeks: low RH (LRH; 25% RH), moderate RH (MRH; 50% RH), and high RH (HRH; 75% RH); ambient temperature was 30°C under all treatments. None of the RH treatments affected hen-day egg production, egg weight, or egg mass (P>0.05). However, feed intake was lower in the HRH group than in the LRH group (P<0.05). Plasma corticosterone (CORT) concentration on day 21, yolk CORT concentration on day 3, and albumen CORT concentration on day 7 following RH exposure were higher in the HRH group than in the LRH group (P<0.05). Moreover, plasma HDL-cholesterol concentration on day 14 was higher in the HRH group than in the LRH group (P<0.05). On days 3 and 14, the Haugh unit decreased (P<0.05) in the LRH group compared with that in the MRH and HRH groups. The HRH-exposed laying hens showed the lowest (P<0.05) eggshell thickness on day 14. The absolute weights of eggshell, yolk, and albumen decreased in the HRH group compared with those in the MRH and LRH groups. Overall, high RH lowered feed intake and egg quality except for the Haugh unit, and induced stress response as manifested by elevated plasma, yolk, and albumen CORT concentrations. To our best knowledge, the present study is the first to demonstrate the role of RH in triggering temperature stress responses in laying hens.

Measurement of corticosterone in the plasma, eggs and faeces of laying hens

Context Stress responses in chickens are commonly assessed from measurements of corticosterone in blood, but there is an increasing research effort to develop non-blood means of assessing the activity of the hypothalamo–pituitary (HPA) axis. It is common to measure corticosterone in the eggs and faeces. Aims We extended previous work by undertaking a study of caged laying hens comparing basal concentrations of corticosterone in plasma, faeces, egg albumen and egg yolk on a between-cage basis. We tested the hypothesis that there are positive relationships between corticosterone in plasma and corticosterone in each of the other matrices. Methods Blood samples were collected from each bird at a single point in time. In Experiment 1, these comparisons (between plasma concentrations of corticosterone on Day 1 and egg albumen, egg yolk and faecal concentrations of corticosterone on Days 1, 3 and 4 of the study) were made for hens of two ages under basal conditions, whereas, in Experiment 2, the comparisons (between plasma concentrations of corticosterone on Day 3 and egg albumen, egg yolk and faecal concentrations of corticosterone on Days 1 and 2 of the study) were made for hens housed at different space allowances with and without access to a nest box. The birds without a nest box had not had experience with a nest box prior to sampling. Key results There was a statistically significant (P = 0.012), but limited, positive relationship between plasma and egg albumen concentrations of corticosterone under basal conditions in Experiment 2. There were no other statistically significant (P &gt; 0.05) relationships in either experiment. These results suggest that measures of corticosterone in the albumen, yolk and faeces of laying hens are unlikely to be robust predictors of basal concentrations of corticosterone in the blood. Conclusions Although there was some indication that concentrations of corticosterone in albumen may be related to concentrations in blood under basal conditions, based on all the results, this suggestion is made cautiously. Implications More comprehensive research is required to establish if measures of corticosterone in egg components and faeces are related to chronic basal activity of the hypothalamo–pituitary axis in laying hens. There is also a need to understand the impact of corticosterone on production, reproduction and welfare in hens from measures in both blood and non-blood matrices.

Sex-specific effects of hatching order on nestling baseline corticosterone in a wild songbird

Variation in nestling growth and survival is often influenced by hatching order, with first-hatched offspring having an advantage over later-hatched younger siblings. In house wrens (Troglodytes aedon), this effect of hatching order is especially evident in asynchronously hatched broods and can lead to sex-specific differences in the size and condition of nestlings. Females appear to allocate the sex of their offspring across the laying order to capitalize on these differences. We hypothesized that levels of circulating corticosterone, the primary metabolic hormone in birds, mediates these sex-specific effects in nestlings. We predicted that: i) baseline levels of corticosterone in nestlings should vary along the hatching order, ii) effects of hatching order on baseline corticosterone should be sex specific, and iii) any sex-specificity of hatching order on baseline corticosterone could be contingent on the degree of hatching synchrony. We tested these predictions in a study in which we measured baseline corticosterone in first- and last-hatched nestlings in synchronously and asynchronously hatching broods. To assess whether any differences in nestling baseline corticosterone levels could be attributed to pre-natal maternal effects, the post-natal environment, or both, we conducted two additional studies in which we measured i) yolk corticosterone in first- and last-laid eggs and ii) baseline corticosterone in nestlings that were cross-fostered to create simulated ‘asynchronously’ hatched broods. There was a significant interaction between sex and relative hatching order in their effects on nestling baseline corticosterone, but no effect of hatching synchrony. Corticosterone levels remained relatively constant across the hatching order in males but decreased in females. There was a significant effect of laying order on yolk corticosterone, with first-laid eggs containing significantly higher levels of yolk corticosterone than last-laid eggs. Cross-fostering of nestlings at different points of development had no significant effect on nestling corticosterone levels. These results indicate that sex-dependent differences in corticosterone levels across the hatching order may arise, at least in part, from embryonic exposure to maternally derived corticosterone, whereas the post-natal rearing environment plays, at best, a minimal role in determining nestling baseline corticosterone levels.

Prenatal yolk corticosterone exposure promotes skeletal growth and induces oxidative imbalance in yellow-legged gull embryos.

Maternally derived hormones induce variation in offspring phenotype, with consequences that can carry over into post-natal life and even into adulthood. In birds, maternal egg corticosterone (CORT) is known to exert contrasting effects on offspring morphology, physiology and behaviour after hatching. However, information on the effects of CORT exposure on pre-hatching embryonic development is limited. We experimentally increased yolk CORT levels in yellow-legged gull (Larus michahellis) eggs, and assessed the effects on embryo pre-hatching development and oxidative status of brain and liver. CORT-supplemented embryos reached a larger skeletal size and liver mass compared with controls. Embryos from CORT-injected last-laid eggs showed decreased activity of the hepatic antioxidant enzymes superoxide dismutase and catalase, while intermediate-laid eggs showed increased levels of lipid peroxidation. However, elevated yolk CORT did not affect oxidative stress endpoints in the brain. Our results indicate that elevated yolk CORT levels affect prenatal embryo development by promoting skeletal growth, and induce laying sequence- and organ-specific oxidative imbalance, with potential adverse consequences during postnatal life, especially for late-hatched offspring.

Experimental manipulation of maternal corticosterone: Hormone transfer to the yolk in the zebra finch Taeniopygia guttata

Maternally-derived hormones affect offspring physiological and behavioural phenotype, plausibly as an adaptive response to maternal environmental conditions. Corticosterone (CORT), the principal avian glucocorticoid produced in response to stress, is recognised as a potential mediator of such maternal reproductive effects. Maternally-derived yolk CORT is implicated in mediating offspring growth and hatchling begging behaviour. However, determining the potential for maternal effects in opportunistic breeders subject to variable environments relies on understanding whether natural variation in maternal circulating hormones may directly impact the embryo during development. Therefore, we tested whether elevated maternal CORT concentrations increase yolk CORT concentrations in zebra finch (Taeniopygia guttata) eggs. We remotely dosed breeding females with biologically-relevant doses of CORT, or the oil vehicle, 0–3 h prior to the predicted time of ovulation, and allowed pairs to produce two clutches, one under each treatment, in a crosswise, balanced design. CORT dosing elevated maternal plasma CORT and increased mean yolk CORT by a factor of 1.75 compared to the egg yolks of control mothers. Importantly, CORT concentrations did not differ between inner and outer layers of yolk. We found no egg lay order effect and maternal CORT dosing did not influence reproductive outputs (clutch initiation date, clutch size or egg mass). Our results confirm the direct impact of biologically-relevant increases in maternal CORT on yolk CORT, providing evidence that maternal CORT concentrations during yolk deposition to the follicle alters embryonic exogenous CORT exposure. Further research is required to determine the impact of maternal CORT on embryonic developmental programming.

Physiological and behavioral responses of laying hens exposed to long-term high temperature.

The present study was conducted to investigate the impact of a 42d period of heat stress on laying hens with respect to rectal temperature, body-surface temperature, heart rate, heterophil to lymphocyte ratio (H/L ratio), corticosterone (CORT) in plasma and yolk samples, and video-assessed behaviors. A total of one hundred twenty 56-week-old ISA-brown laying hens were continuously exposed to one of three temperature regimes: optimal (LT; 22°C), moderate (MT; 27°C), and high (HT; 32°C). The relative humidity was maintained at 50% in all treatments. HT vs. MT and LT increased rectal temperature, heart rate, and body-surface temperature on all days (P<0.05). HT vs. LT raised (P<0.05) the H/L ratio in blood at day 42 following heat exposure. On the other hand, both HT- and MT-exposed laying hens had higher (P<0.05) plasma CORT compared with those on LT group only at 28 and 42d following heat treatment. Yolk CORT was elevated (P<0.05) in the HT vs. MT and LT groups at 3 and 14d following heat treatment. Panting and wing elevation were the most relevant behaviors in laying hens exposed to HT vs. MT and LT. The study shows that rectal and body-surface temperature, heart rate, and behavior, but not CORT or H/L ratio, are the reliable indicators for assessing the stress status of laying hens over extended period of heat stress.

The relation between liver damage and reproduction in female Japanese quail (Coturnix japonica) exposed to high ambient temperature

Reproductive failure associated with heat stress is a well-known phenomenon in poultry. High temperatures also induce various metabolic disturbances in many animals. Because the liver plays a central role in metabolism, the present study aimed to clarify the relationship between liver and reproduction in Japanese quails exposed to high temperatures. In the consecutive 20-D experimental period, quails were treated with 25°C (control) or 34°C (heat) from 12:00 to 16:00. Eggs were collected for hatching. On completion of the experimental period, quails were humanely euthanized for hormone analyses (e.g., serum and ovarian follicles). Serum metabolites were analyzed using GC/MS. Liver and ovary samples were collected for mRNA levels, histomorphology, and metabolic analysis. Ovary and oviduct weights significantly decreased after daily heat exposure. The number and weight of hierarchical follicles also decreased. Consequently, egg weight decreased. Although there was no difference in fertilization rate, chick birth weight significantly decreased in the heated group. Corticosterone and 17β-estradiol in the serum significantly increased in the heated group. Yolk corticosterone and 17β-estradiol concentration and content were higher in the heated group. Ovary sterologenic enzymes gene P450scc and estrogen receptor expression level increased. The FSH receptor decreased in heat-stressed quails. MetaboAnalyst analysis indicated that high temperature affects propanoate metabolism, beta-alanine metabolism, aspartate metabolism, and histidine metabolism. Triglyceride and cholesterol levels in the liver increased in the heated group. The heated group also had an increased mRNA expression of AGPAT5, apoptosis gene caspase3, and the immunocytokine genes IL-6 and TLR4. However, NF-κB gene expression decreased. These results suggest that high temperatures affect lipid metabolism and apoptosis and cause inflammation in the liver. High temperature induced ovarian dysfunction, which resulted in the decline of hierarchical follicle number and weight, egg weight, and chick birth weight. The increased level of 17β-estradiol suggests liver damage. Protecting liver function from damage may assist quails cope in summer.

Maternal betaine suppresses adrenal expression of cholesterol trafficking genes and decreases plasma corticosterone concentration in offspring pullets

BackgroundLaying hens supplemented with betaine demonstrate activated adrenal steroidogenesis and deposit higher corticosterone (CORT) in the egg yolk. Here we further investigate the effect of maternal betaine on the plasma CORT concentration and adrenal expression of steroidogenic genes in offspring pullets.ResultsMaternal betaine significantly reduced (P < 0.05) plasma CORT concentration and the adrenal expression of vimentin that is involved in trafficking cholesterol to the mitochondria for utilization in offspring pullets. Concurrently, voltage-dependent anion channel 1 and steroidogenic acute regulatory protein, the two mitochondrial proteins involved in cholesterol influx, were both down-regulated at mRNA and protein levels. However, enzymes responsible for steroid syntheses, such as cytochrome P450 family 11 subfamily A member 1 and cytochrome P450 family 21 subfamily A member 2, were significantly (P < 0.05) up-regulated at mRNA or protein levels in the adrenal gland of pullets derived from betaine-supplemented hens. Furthermore, expression of transcription factors, such as steroidogenic factor-1, sterol regulatory element-binding protein 1 and cAMP response element-binding protein, was significantly (P < 0.05) enhanced, together with their downstream target genes, such as 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase, LDL receptor and sterol regulatory element-binding protein cleavage-activating protein. The promoter regions of most steroidogenic genes were significantly (P < 0.05) hypomethylated, although methyl transfer enzymes, such as AHCYL, GNMT1 and BHMT were up-regulated.ConclusionsThese results indicate that the reduced plasma CORT in betaine-supplemented offspring pullets is linked to suppressed cholesterol trafficking into the mitochondria, despite the activation of cholesterol and corticosteroid synthetic genes associated with promoter hypomethylation.

Effect of maternal environment on yolk immunoreactive corticosterone and its influence on adrenocortical and behavioral activity in chicks of Greater Rhea (Rhea americana)

Maternal corticosterone in avian eggs may modify offspring phenotype in order to increase survival in poor environments. In the Greater Rhea (Rhea americana), we previously found that yolk immunoreactive corticosterone is influenced by the quality of the maternal environment: eggs laid by females of the intensive rearing system (IRS), living in poor captive conditions, had higher yolk immunoreactive corticosterone than those produced by females of the semi-extensive rearing system (SRS), living in better conditions. Here, we evaluate if these different hormone levels are associated with the production of different phenotypes. We collected eggs from the IRS and SRS for hormonal quantification and artificial incubation. Then, half of the chicks selected from each environment were exposed to a capture and restraint protocol, and the rest remained undisturbed and were used as controls. In the IRS, we found that higher yolk immunoreactive corticosterone was associated with the production of chicks that had reduced hatchability, lower hatchling mass and higher baseline fecal glucocorticoid metabolites (FGM) than those produced by SRS females. Moreover, after capture and restraint, IRS chicks did not modify their FGM nor their behaviors compared to their controls, while SRS chicks increased their FGM and spent more time ambulating and less time pecking, compared to their controls. These results indicate that yolk immunoreactive corticosterone could modify offspring phenotype. Although future studies are needed to elucidate their implications for fitness, our results suggest that yolk corticosterone could be mediating an adaptive maternal effect that allows individuals to better cope with poor conditions.

Yolk corticosterone in the Gouldian Finch (Erythrura gouldiae)

ABSTRACTMaternal hormones are thought to play an important role in determining the rate of evolutionary adaptation. Previous avian studies have shown that the transfer of maternally derived hormones, such as progesterone and testosterone, to the egg, affects many aspects of offspring development. In contrast, the impact of maternal corticosterone (CORT) is much less studied. CORT, the principal avian glucocorticoid hormone, is thought to be passively transferred to the egg yolk from the maternal plasma. Maternal CORT may play a role in determining the development of young birds by adaptively programming offspring for their environment. We developed a protocol which effectively quantifies yolk CORT concentrations both within and across clutches, using solid-phase extraction and radioimmunoassay. We hypothesised that Gouldian Finch (Erythrura gouldiae) mothers would differ in their yolk CORT concentrations and that maternal condition would relate to absolute yolk CORT deposition. We found variation in yolk CORT concentrations between clutches, whilst yolk CORT increased with egg number in the first breeding season and negatively correlated with yolk mass. Yet, contrary to our predictions, neither maternal mass nor clutch size showed any relationship to yolk CORT concentrations or to egg or yolk mass. Our data suggest that yolk CORT varies with maternal identity for reasons which do not appear to be linked to maternal condition. Further research is needed to determine the link between maternal and egg yolk concentrations at the individual level. Such tests would be valuable for understanding the role of CORT in the reproductive effects previously observed in this threatened species.

Evidence of embryonic regulation of maternally derived yolk corticosterone.

In recent years, the potential for maternal stress effects to adaptively alter offspring phenotype has received considerable attention. This research has identified offspring traits that are labile in response to maternal stress; however, an understanding of the mechanisms underlying these effects is lagging and is crucial to appreciating the significance of this maternal effect. In the present study, we sought to better understand maternal stress effects by examining the potential for embryonic regulation of corticosterone exposure, determining the phenotypic consequences of elevated corticosterone during development, and characterizing the levels of maternally transferred corticosterone in unmanipulated eggs using Trachemys scripta By dosing eggs with tritiated corticosterone and tracking the steroid throughout development, we found that most corticosterone is metabolized, and less than 1% of the corticosterone dose reaches the embryo as free corticosterone. We also found that exogenous dosing of corticosterone, in concentrations sufficient to overwhelm embryonic metabolism, reduces embryonic survival and negatively impacts hatchling traits important to fitness. Our results demonstrate that concentrations of maternal corticosterone in the yolks of unmanipulated eggs are low and are significantly lower than the doses of corticosterone required to elicit phenotypic effects in hatchlings. Taken together, these results provide evidence that both the embryo and the female may minimize corticosterone accumulation in the embryo to avoid reductions in embryonic survival and negative impacts on offspring phenotype and fitness.