Changes in Prostaglandin F Concentration in the Uterus (Shell Gland) of the Hen Oviduct in Relation to Oviposition and Estrogen

A synthetic review: natural history of amniote reproductive modes in light of comparative evolutionary genomics

There is a current lack of consensus on whether the ancestral parity mode was oviparity (egg-laying) or viviparity (live-birth) in amniotes and particularly in squamates (snakes, lizards, and amphisbaenids). How transitions between parity modes occur at the genomic level has primary importance for how science conceptualises the origin of amniotes, and highly variable parity modes in Squamata. Synthesising literature from medicine, poultry science, reproductive biology, and evolutionary biology, I review the genomics and physiology of five broad processes (here termed the 'Main Five') expected to change during transitions between parity modes: eggshell formation, embryonic retention, placentation, calcium transport, and maternal-fetal immune dynamics. Throughout, I offer alternative perspectives and testable hypotheses regarding proximate causes of parity mode evolution in amniotes and squamates. If viviparity did evolve early in the history of lepidosaurs, I offer the nucleation site hypothesis as a proximate explanation. The framework of this hypothesis can be extended to amniotes to infer their ancestral state. I also provide a mechanism and hypothesis on how squamates may transition from viviparity to oviparity and make predictions about the directionality of transitions in three species. After considering evidence for differing perspectives on amniote origins, I offer a framework that unifies (i) the extended embryonic retention model and (ii) the traditional model which describes the amniote egg as an adaptation to the terrestrial environment. Additionally, this review contextualises the origin of amniotes and parity mode evolution within Medawar's paradigm. Medawar posited that pregnancy could be supported by immunosuppression, inertness, evasion, or immunological barriers. I demonstrate that this does not support gestation or gravidity across most amniotes but may be an adequate paradigm to explain how the first amniote tolerated internal fertilization and delayed egg deposition. In this context, the eggshell can be thought of as an immunological barrier. If serving as a barrier underpins the origin of the amniote eggshell, there should be evidence that oviparous gravidity can be met with a lack of immunological responses in utero. Rare examples of two species that differentially express very few genes during gravidity, suggestive of an absent immunological reaction to oviparous gravidity, are two skinks Lampropholis guichenoti and Lerista bougainvillii. These species may serve as good models for the original amniote egg. Overall, this review grounds itself in the historical literature while offering a modern perspective on the origin of amniotes. I encourage the scientific community to utilise this review as a resource in evolutionary and comparative genomics studies, embrace the complexity of the system, and thoughtfully consider the frameworks proposed.

Metabolomics reveals the reasons for the occurrence of Pendulous-comb related to egg production performance

The chicken comb is an essential secondary sexual characteristic to measure sexual maturity and is closely related to reproductive performance. Pendulous comb (PC) and upright comb (UC) are 2 common comb phenotypes in hens, which have been highly associated with egg production performance. However, the reasons for the formation of PC remain undetermined. In this study, we first characterized the PC and UC chicken at start (at 175 d age), peak (at 217 d age), and postlaying (at 300 d age) and found that PC and UC could transform for each other. Furthermore, we suggested that PC chicken demonstrated better egg production performance than UC chicken, especially characterizing comb type in the start-laying period. Moreover, we performed histological evaluation of PC and UC tissue, which suggested that the low density of collagen fibers and acid mucopolysaccharides might lead to the formation of PC. To further explore the possible reasons for PC formation, we performed an untargeted metabolomic analysis of serum between PC and UC chicken in the start, peak, and postlaying periods. The enrichment analysis of period-unique differentially expressed metabolites (DEMs) between PC and UC showed that the different metabolic pathways and nutritional levels might contribute to the formation of PC in the different laying periods. Our research provided critical insights into the phenotypic diversity of chicken comb, establishing a foundation for early selection of chicken egg production performance.

Understanding avian egg cuticle formation in the oviduct: a study of its origin and deposition

The cuticle is a unique invisible oviduct secretion that protects avian eggs from bacterial penetration through gas exchange pores. Despite its importance, experimental evidence is lacking for where, when, and what is responsible for its deposition. By using knowledge about the ovulatory cycle and oviposition, we have manipulated cuticle deposition to obtain evidence on these key points. Cuticle deposition was measured using staining and spectrophotometry. Experimental evidence supports the location of cuticle deposition to be the shell gland pouch (uterus), not the vagina, and the time of deposition to be within the final hour before oviposition. Oviposition induced by arginine vasotocin or prostaglandin, the penultimate and ultimate factors for the induction of oviposition, produces an egg with no cuticle; therefore, these factors are not responsible for cuticle secretion. Conversely, oviposition induced by GNRH, which mimics the normal events of ovulation and oviposition, results in a normal cuticle. There is no evidence that cuticle deposition differs at the end of a clutch and, therefore, there is no evidence that the ovulatory surge of progesterone affects cuticle deposition. Overall, the results demonstrate that the cuticle is a specific secretion and is not merely an extension of the organic matrix of the shell. Cuticle deposition was found to be reduced by an environmental stressor, and there is no codependence of the deposition of pigment and cuticle. Defining the basic facts surrounding cuticle deposition will help reduce contamination of hen's eggs and increase understanding of the strategies birds use to protect their eggs.

Changes in angiotensin II receptor bindings in the hen neurohypophysis before and after oviposition

The present study was performed to elucidate whether the angiotensin II (ANG II) receptor exists in the plasma membrane fraction of the neurohypophysis in hens, to estimate the time of action of ANG II on the neurohypophysis before and after oviposition, and to examine relationships between the action of ANG II on the neurohypophysis and those of estrogen and prostaglandin F(2α) (PGF(2α)) in relation to arginine vasotocin (AVT) release. The specific binding had a binding specificity to chicken ANG II (cANG II), reversibility, and saturation in the [(125)I]cANG II binding assay. Scatchard analysis revealed that the binding sites are of a single class. The equilibrium dissociation constant (K(d)) obtained by kinetic analysis and Scatchard analysis suggested a high affinity, and the maximum binding capacity (B(max)) obtained by Scatchard analysis suggested a limited capacity. These results suggest that an ANG II receptor exists in the neurohypophysis of hens. The K(d) and the B(max) value was significantly smaller in laying hens than in nonlaying hens, which suggests that bindings of the cANG II receptor change, depending on the difference in laying condition. Values of the K(d) and the B(max) decreased approximately 15 min before oviposition in laying hens, and decreased 1 h after an intramuscular injection of estradiol-17β and 5 min after an intravenous injection of cANG II in nonlaying hens. The amount of specific binding of PGF(2α) receptor in the neurohypophysis also decreased and AVT concentration in blood increased after the cANG II injection. It seems likely that the action of cANG II in the neurohypophysis increases due to the effect of estrogen approximately 15 min before oviposition, and the cANG II action stimulates AVT release through the increase in the PGF(2α) action in this tissue.

Effects of dietary n-6:n-3 ratio on immune and reproductive systems of pullet chicks

The objective of this study was to examine the effects of dietary n-6:n-3 ratio on immune and reproduction systems of Leghorn pullet chicks. A total of 216 Hy-Line W-36 pullet chicks (1 d old) were randomly assigned to 3 diets (n-6:n-3 ratios of 10, 6, and 2) until 22 wk of age. The Optomega-50 (Optivite International Ltd., Nottinghamshire, UK) containing 50% salmon fish oil was used as an n-3 source. Pullets were injected with SRBC suspension at 6 and 9 wk and anti-SRBC titers were measured 7 and 14 d after each immunization. The antibody (Ab) titers for Newcastle disease (ND), avian influenza, infectious bronchitis (IB), and infectious bursal disease (IBD) were determined at 4, 6, 10, 14, and 18 wk of age. Pullets fed diet with the n-6:n-3 ratio of 2 had higher feed consumption and lower BW gain (P < 0.05) compared those fed diets with the ratios of 6 and 10. The results demonstrated that the different dietary n-6:n-3 ratios did not have a significant effect on the anti-SRBC titers in pullets serum (P > 0.05). The Ab production against avian influenza vaccine was increased in pullets fed diet containing the n-6:n-3 ratio of 10 at wk 10 and 14 and increased for ND at only 14 wk (P < 0.05). On the other hand, the Ab response to IBD (14 wk) and IB (14 wk) vaccines was increased when pullets were fed diet containing a ratio of 6 (P < 0.05). The pullets fed diet with the n-6:n-3 ratio of 2 showed lower egg production and late sexual maturity (P > 0.05) whereas ovary weight (P = 0.01) and number of large yellow follicles (P = 0.049) were significantly decreased at first oviposition. Our results revealed that the supplementation of Optomega-50 as a source of n-3 to decrease the n-6:n-3 ratio in diet significantly increased Ab production for ND, IB, and IBD in pullet chicks with slight reduction in reproductive organs weight at early production.

Prostaglandin F(2alpha) receptor in the neurohypophysis of hens

To elucidate whether the receptor for prostaglandin (PG) F(2alpha), one of PG, exists in the neurohypophysis in hens and whether the binding of receptor changes with relation to oviposition, the PGF(2alpha) binding component in the membrane fraction of the neurohypophysis of laying hens was analyzed by radioligand binding assay using [5,6,8,9,11,12,14,15(n)-(3)H]PGF(2alpha). The binding component had characteristics of a receptor such as binding specificity, high affinity, and limited capacity for PGF(2alpha). Scatchard analysis indicated that the binding site was of a single class. The binding capacity of the receptor was smaller in laying hens than in nonlaying hens, whereas the binding affinity was not significantly different between these hens. When non-laying hens received an i.m. injection of estradiol-17beta or progesterone (0.5 mg/hen), the specific binding of the PGF(2alpha) receptor in the neurohypophysis was decreased. In laying hens, the specific binding decreased and the blood arginine vasotocin (AVT) concentration increased just after oviposition but did not change during a 24-h day in nonlaying hens. An i.v. injection of PGF(2alpha) (2 microg/hen) induced oviposition and caused an increase in the blood AVT concentration with a decrease in the specific binding of PGF(2alpha) receptor. The present study suggests a possibility that PGF(2alpha) may directly cause the AVT release from the neurohypophysis at oviposition time in hens.

Effect of estrogen and its antagonist on the expression of arginine vasotocin (AVT) and its oxytocic-like receptor VT3 in the shell gland of Japanese quail, Coturnix coturnix japonica

Avian neurohypophysial hormone arginine vasotocin (AVT) is known to regulate shell gland contractility during oviposition. While studying the role of estrogen in the expression and regulation of AVT and its oxytocic-like receptor VT3, using in situ hybridization and immunohistochemistry, it was observed that the expression of AVT and its receptor was not detected in the shell gland of sexually immature Japanese quail. However, administration of estrogen to these birds not only stimulates the growth and activity (as assessed by increased mucosal fold length, total protein content and alkaline phosphatase level) of the shell gland but also upregulates the expression of AVT and VT3. Further, administration of estrogen antagonist tamoxifen to sexually mature bird shows opposite results. On the other hand, localization of ir-AVT, observed in the ovary of sexually mature bird, was not detected in the estrogen treated sexually immature quail. It is concluded that estrogen not only affects the growth and differentiation of avian oviduct, but also regulates the expression of shell gland AVT and its receptor VT3. Present findings suggest that the locally synthesized AVT acts in a paracrine way to upregulate VT3 receptor and thus facilitates the endocrine function of neurohypophysial AVT during oviposition.