The expression of pituitary FSHbeta and LHbeta mRNA and gonadal FSH and LH receptor mRNA in the chicken embryo

Laying performance, genetic parameters, and the expression of FSHβ, LHβ, FSHR, and LHR genes in Japanese quails selected for early egg production

Investigating the impact of early egg production selection (the first 90 d of laying) on egg production features, cumulative selection response (CSR), and the mRNA expression of gonadotropins (FSHβ and LHβ), and their receptors (FSHR and LHR), in Japanese quails was the goal. The selection experiment involved 1293 females in all, 257 from the base group and 1036 from the 4 selected generations. Age and body weight at sexual maturity (ASM, BWSM), weight of the first egg (WFE), days to the first 10 eggs (DF10E), egg mass for the first 10 eggs (EMF10E), egg weight (EW), egg number at the first 90 d of laying (EN90D), and egg mass at the first 90 d of laying (EM90D) were all recorded. Most egg production traits had heritability estimates that were low to moderate and ranged from 0.17 to 0.33., where the highest estimates were reported for EN90D (0.33) and BWSM (0.32). With the exception of EN90D, low to moderate positive genetic correlations were observed between ASM and other egg production traits (0.17-0.44). The fourth generation showed significantly (P < 0.05) lower ASM and DF10E but higher BWSM, WFE, EN90D, EM10E, and EM90D when compared with the base generation. CSR were significant (P < 0.05) for ASM (-6.67 d), BWSM (27.13 g), WFE (0.93 g), DF10E (-1.25 d), EN90D (7.24 egg), EM10E (10.57 g), and EM90D (140.0 g). FSHβ, LHβ, FSHR, and LHR gene mRNA expression was considerably (P < 0.05) greater in the fourth generation compared to the base generation. In conclusion, selection programs depending on the efficiency of egg production (EN90D) could improve the genetic gain of egg production traits and upregulate the mRNA expression of FSHβ, LHβ, FSHR, and LHR genes in selected quails (fourth generation). These findings might help to enhance breeding plans and create commercial lines of high egg production Japanese quails.

Extraordinary variability in gene activation and repression programs during gonadal sex differentiation across vertebrates

Genes involved in gonadal sex differentiation have been traditionally thought to be fairly conserved across vertebrates, but this has been lately questioned. Here, we performed the first comparative analysis of gonadal transcriptomes across vertebrates, from fish to mammals. Our results unambiguously show an extraordinary overall variability in gene activation and repression programs without a phylogenetic pattern. During sex differentiation, genes such as dmrt1, sox9, amh, cyp19a and foxl2 were consistently either male- or female-enriched across species while many genes with the greatest expression change within each sex were not. We also found that downregulation in the opposite sex, which had only been quantified in the mouse model, was also prominent in the rest of vertebrates. Finally, we report 16 novel conserved markers (e.g., fshr and dazl) and 11 signaling pathways. We propose viewing vertebrate gonadal sex differentiation as a hierarchical network, with conserved hub genes such as sox9 and amh alongside less connected and less conserved nodes. This proposed framework implies that evolutionary pressures may impact genes based on their level of connectivity.

Comparative transcriptomic analysis of ovaries from high and low egg-laying Lingyun black-bone chickens

Egg‐laying rate is mainly determined by ovarian function and regulated by the hypothalamic‐pituitary‐gonadal axis; however, the mechanism by which the ovary regulates the egg‐laying rate is still poorly understood. The purpose of this study was to compare the differences in the transcriptomes of the ovary of Lingyun black‐bone chickens with relatively high and low egg‐laying rates and screen candidate genes related to the egg‐laying rate. RNA‐sequencing (RNA‐Seq) was conducted to explore the chicken transcriptome from the ovarian tissue of six Lingyun black‐bone chickens with high (group G, n = 3) and low (group D, n = 3) egg‐laying rates. The results showed that 235 differentially expressed genes (DEGs) were identified between the chickens with high and low egg‐laying rates; among them, 209 DEGs were up‐regulated and 26 DEGs were down‐regulated. Gene Ontology analysis showed that the up‐regulated 209 DEGs were enriched in 50 GO terms and the down‐regulated 26 DEGs were enriched in 40 GO terms. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that up‐regulated DEGs were significantly enriched in 25 pathways and down‐regulated DEGs were significantly enriched in three pathways. Among the pathways, we found the longevity regulating pathway‐multiple species pathway, Estrogen signalling pathway and PPAR signalling pathway may have an essential function in regulating the egg‐laying rate. The results highlighted DEGs in the ovarian tissues of relatively high and low laying Lingyun black‐bone chicken and identified essential candidate genes related to the egg‐laying rate, thereby providing a theoretical basis for improving the egg‐laying rate of Lingyun black‐bone chicken.

Sodium Fluoride In Vitro Treatment Affects the Expression of Gonadotropin and Steroid Hormone Receptors in Chicken Embryonic Gonads

Simple Summary

Effects of in vitro sodium fluoride (NaF) treatment on the mRNA expression of luteinizing hormone receptor (LHR), follicle-stimulating hormone receptor (FSHR), estrogen receptors (ESR1 and ESR2), progesterone receptor (PGR), and the immunolocalization of PGRs were examined in gonads of 14-day-old chicken embryos. In the ovary, the NaF treatment significantly increased mRNA levels of all investigated receptors. In the testes, the lowest applied dose of NaF (1.7 mM) significantly decreased the expression of FSHR, ESR1, ESR2, and PGR. Alternatively, the higher NaF dose (7.1 mM) elevated PGR mRNA level in the male gonad. Immunohistochemical analysis revealed that the NaF exposure increased PGR expression in the ovarian cortex, while it decreased its expression in the testes. Collectively, these data indicate that: (i) NaF may disturb the chicken embryonic development, and (ii) different mechanisms of this toxicant action exist within the female and male gonads.

Abstract

Sodium fluoride (NaF), in addition to preventing dental decay may negatively affect the body. The aim of this study was to examine the effect of a 6 h in vitro treatment of gonads isolated from 14-day-old chicken embryos with NaF at doses of 1.7 (D1), 3.5 (D2), 7.1 (D3), and 14.2 mM (D4). The mRNA expression of luteinizing hormone receptor (LHR), follicle-stimulating hormone receptor (FSHR), estrogen receptors (ESR1 and ESR2), progesterone receptor (PGR), and the immunolocalization of progesterone receptors were examined in the tissue. In the ovary, the expression of FSHR and LHR increased following the NaF treatment. In the case of FSHR the highest stimulatory effect was noticed in the D2 group, while the expression of LHR increased in a dose-dependent manner. A gradual increase in ESR1 and PGR mRNA levels was also observed in the ovary following the NaF treatment, but only up to the D3 dose of NaF. The highest ESR2 level was also found in the D3 group. In the testes, the lowest dose of NaF significantly decreased the expression of FSHR, ESR1, ESR2, and PGR. On the other hand, an increase in PGR expression was observed in the D3 group. The expression of LHR in the testes was not affected by the NaF treatment. Immunohistochemical analysis showed that NaF exposure increased progesterone receptor expression in the ovarian cortex, while it decreased its expression in the testes. These results reveal that NaF may disturb the chicken embryonic development and different mechanisms of this toxicant action exist within the females and males.

Effects of follicle-stimulating hormone beta subunit and nuclear receptor coactivator 1 gene polymorphisms and expressions on pink-eyed white mink reproductive traits

The present study was designed to investigate comparative expressions of follicle-stimulating hormone beta subunit (FSHβ) and nuclear receptor coactivator 1 (NCOA1) genes by real-time polymerase chain reaction, using polymerase chain reaction single-strand conformation polymorphism methods to investigate the effects of gene polymorphisms on reproductive traits, including total number of kits born (TNB) and number of born alive (NBA) in pink-eyed white mink. Four single-nucleotide polymorphisms were identified in the FSHβ and NCOA1 genes. The g.1228G>A polymorphism of FSHβ was associated with NBA and TNB (P < 0.01). The g.151536T>C polymorphism of NCOA1 was associated with NBA and TNB (P < 0.01). The NCOA1 mRNA levels in hypothalamus, ovary, and uterus during the first half of gestation were higher than during the middle term and last half of gestation (P < 0.01). The FSHβ mRNA levels in the hypothalamus and uterus were higher during the first half of gestation than during the middle term and last half of gestation (P < 0.05). In conclusion, the g.1866T>C polymorphism of FSHβ and the g.151536T>C polymorphism of NCOA1 could be molecular markers for reproductive traits, and expressions of FSHβ and NCOA1 might be involved in the regulation of embryo attachment mechanisms in pink-eyed white mink breeding.

Effects of gonadotropins on testis cell subpopulations of newly hatched chicks treated during embryonic development

The aim of the present study was to evaluate histological and stereological changes, as well as the variations in the number and size of cells from diverse cell subpopulations in testes of newly hatched chicks treated with follicle stimulating hormone (FSH) and luteinizing hormone (LH) during embryonic development. Stereological results indicated that in FSH-treated chicks total volume of the tubular compartment constitutes most of the testis. In contrast, the total volume of interstitial tissue constitutes most of the testis of LH-treated chicks. Results indicate that the number of germ and Sertoli cells increases as a result of FSH and LH treatment, but in FSH-treated testis, Sertoli cells were the most numerous cell type in seminiferous tubules; whereas germ cells were the most numerous cell type in testis of LH-treated chicks. Results also indicate there was a larger total volume of Leydig cells in the testes of FSH- and LH-treated chicks. The larger volume of Leydig cells in FSH-treated chicks is due to a larger cellular volume of these cells, and not due to the number, which remains constant. In contrast, in testes of LH-treated chicks, there is a larger number and volume of Leydig cells. These results indicate the testes of chick embryos respond to FSH and LH treatment, with there being modifications in the seminiferous tubules and interstitial tissue, but these changes differ markedly, indicating that FSH and LH have differential effects on chick testes.

Identification of differentially expressed genes associated with egg production in black-boned chicken

1. Muchuan black-bone chicken is well known in China for its meat quality and medicinal properties; however, its egg-laying performance is not ideal. To better understand the molecular mechanisms of black-boned chicken egg-laying, high-throughput RNA sequencing was performed to compare differences in the pituitary transcriptome between three high-rate (group H) and three low-rate (group L) egg production chickens. 2. In total, 171 differentially expressed genes (DEGs) were identified between the two groups, of which 113 were upregulated and 58 were downregulated in group L. Some of these genes are known to be related to hormone secretion or the regulation of reproductive processes; these include prolactin-releasing hormone (PRLH), distal-less homeobox 6 (DLX6), interferon regulatory factor 4 (IRF4), and cilia and flagella associated protein 69 (CFAP69). Notably, expression pattern analysis indicated that both PRLH and DLX6 may influence egg-laying performance. 3. The dataset provided a foundation for discovering important genes and pathways involved in the chicken egg-laying process, and may help to improve understanding of the molecular mechanisms of chicken reproduction.

The effect of total flavonoids of Epimedium on granulosa cell development in laying hens

To investigate the impact of total flavonoids of Epimedium (TFE) on the development of follicles of laying hens, 3 types of follicles including primary, prehierarchical, and preovulatory follicles were selected to obtain the follicular granulosa cells cultured in vitro. First, extraction of TFE was conducted by alcohol-soluble and ultrasonic methods. The effects of TFE on activity and proliferation of follicular granulosa cells were detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and measuring the expression of proliferating cell nuclear antigen mRNA through real-time quantitative polymerase chain reaction, and the expression of the follicle-stimulating hormone receptor, luteinizing hormone receptor, steroidogenic acute regulatory protein, and cytochrome P450 family 11 subfamily A member 1 mRNA was detected to study the functions of TFE affecting the differentiation and hormone secretion by granulosa cells. The results showed that TFE significantly improved the proliferation of 3 types of granulosa cells and promoted the differentiation of granulosa cells and accelerated the conversion of primary follicles to prehierarchical follicles. Total flavonoids of Epimedium played an important role in promoting progesterone secretion by prehierarchical and preovulatory granulosa cells. The results indicated that TFE could promote proliferation and differentiation of follicular granulosa cells and improve hormone secretion and follicle development, which provided reference data for TFE used as a feed additive or safe Chinese veterinary medicine to promote the laying rate.

Cloning and expression analysis of the follicle-stimulating hormone receptor (FSHR) gene in the reproductive axis of female yaks (Bos grunniens)

Follicle-stimulating hormone receptor (FSHR) plays a central role in promoting follicle maturation through the follicle-stimulating hormone (FSH)-mediated cAMP pathway in animals. The objectives of the present study were to clone the FSHR gene of yaks (Bos grunniens) and compare differences in FSHR mRNA expression in the reproductive axis between yaks and cattle. Hypothalamus, anterior pituitary, oviduct, ovary, and uterus tissue samples were collected from adult female yaks (n = 5) and cattle (n = 5) during the follicular phase. Using reverse transcriptase-polymerase chain reaction (RT-PCR), we found that the FSHR coding region of the yak is 2088 bp and encodes 695 amino acids. Its amino acid sequence showed 99.38%-72.22% similarity to the homologous genes of cattle, goats, sheep, cats, donkeys, horses, humans, chickens, monkeys, mice, rats, and wild boar. Real-time PCR analysis revealed that the FSHR gene was expressed in all tissues examined. Expression of the FSHR gene in the yak was higher in the uterus than other tissues (P < 0.05) but, in cattle, was higher in the ovary than other tissues (P < 0.05). The FSHR gene expression level in the cattle ovary was significantly higher than that in the yak ovary (P < 0.01). These results indicate that the FSHR gene is relatively conserved in the course of animal evolution. The variation in sequence and expression level of FSHR between the two species might be associated with the difference in their reproduction.

Interferon-γ acts as a regulator in the trade-off between phagocytosis and production performance in dwarf chickens

Background

Interferon-γ (IFN-γ) is critical for innate and adaptive immunity against viral and bacterial infections. IFN-γ reportedly affects the phagocytic ability of monocytes and macrophages as well as regulates pituitary function in humans and mice. The present study analyzed the impact of IFN-γ on monocyte and macrophage phagocytosis, production performance, and pituitary function in vivo and in vitro (in dwarf chickens). IFN-γ was injected into dwarf chickens through a vein, and then, the laying rate, average egg weight, and levels of follicle-stimulating hormone (FSH) and IFN-γ were measured in treatment and control groups. For the in vitro experiment, the pituitary tissues were supplemented with IFN-γ, and the mRNA expression levels of follicle-stimulating hormone beta subunit (FSH-β), interferon gamma receptor 1 (IFNGR1), and interferon gamma receptor 2 (IFNGR2) in the pituitary were assessed.

Results

Monocyte and macrophage phagocytosis product (PP) was decreased by IFN-γ treatment in a dose-dependent manner in vitro. In the in vivo experiment, the level of IFN-γ in the treatment group was higher than that in the control group at 7 d (P < 0.05), 14 d (P < 0.01), and 21 d (P < 0.01) post-injection. Compared with the control group, monocyte and macrophage PP was lower in the treatment group after injection (P < 0.01). The laying rate was higher in the treatment group than in the control group at 2 and 3 wk post-injection (P < 0.05). There was a significant difference between the treatment and control groups in the levels of FSH at 1, 3, 7, and 14 d post-injection (P < 0.01). In the in vitro experiment, increased mRNA expression levels of FSH-β, IFNGR1, and IFNGR2 were observed in the treatment group after stimulation with 100 U/mL IFN-γ for 24 h compared to those in the control group (P < 0.05).

Conclusions

IFN-γ inhibited the phagocytosis of monocytes and macrophages; up-regulated the mRNA expression levels of the FSH-β, IFNGR1, and IFNGR2; enhanced the secretion of FSH; and improved the laying rate. IFN-γ might be an important regulator in the trade-off between the immune effect and production performance in dwarf chickens.

Molecular characterization, expression profile of the FSHRgene and its association with egg production traits in muscovy duck

Follicle-stimulating hormone (FSH) and its receptor play a key role in the follicular development and regulation of steroidogenesis in the ovary and spermatogenesis in the testis. The purpose of this study was to characterize themuscovy duck FSHR gene, identify SNPs and their association with egg production traits in muscovy ducks. Here, we cloned the complementary DNA (cDNA) sequence of FSHR, and examined the expression patterns of FSHR gene in adult female muscovy duck tissues. The cloned cDNA of the muscovy duck FSHR gene shared high similarity to those of pekin duck (Anas platyrhynchos) (95.7%) and chicken (93.2%). Three different muscovy duck FSHR transcripts were identified. Quantitative real-time PCR (RT-qPCR) results showed that the FSHR gene was expressed in all the 14 tested tissues, and the highest expression level was seen in the ovary. A total of 16 SNPs were identified, among which, four SNPs were located in the coding region of FSHR. The SNP C320T is significantly associated with egg production at 59 weeks of age (P < 0.05), whereas the SNP A227G is significantly associated with age at first egg stage (P < 0.05). These results suggest that the two SNPs (A227G and C320T) of FSHR gene are associated with egg production traits and could be potential markers that can be used for marker-assisted selection programmes to increase egg production in muscovy duck.

Gene expression profiling in embryonic chicken ovary during asymmetric development

The reproductive system in female birds arises as bilateral asymmetrical anlagen, excluding the birds of prey. Earlier, histological and messenger RNA (mRNA) expression profile studies of several genes related to gonadal sex differentiation in chicken embryos tried to elucidate the query of this asymmetry in a scattered manner. To understand the matter precisely, we have focused on mRNA expression of a cohort of genes (FSHR, CYP19A1, caspase 3, caspase 8) in second half of the embryonic days (E10-E18). The established role of leptin in development of the embryo and its expression in the embryonic ovary also drove us to check leptin receptor (LEPR) expression in the ovary. Increased expression of FSHR and CYP19A1 in the left ovary compared with that in the right ovary was identified (P < 0.05), promoting preferential left ovarian development and functionality. Significant high expression (P < 0.05) of the apoptotic genes in the right ovary were also involved here. Leptin probably has no direct influence on ovarian asymmetry as no significant variation in gonadal mRNA expression of LEPR was observed within the same experimental days. We propose that asymmetric expression of this cohort of genes (FSHR, CYP19A1, caspase 3, caspase 8) leads to the development of dimorphic gonads during embryogenesis.

Loss of follicle-stimulating hormone receptor function causes masculinization and suppression of ovarian development in genetically female medaka

FSH, a glycoprotein hormone, is circulated from the pituitary and functions by binding to a specific FSH receptor (FSHR). FSHR is a G protein-coupled, seven-transmembrane receptor linked to the adenylyl cyclase or other pathways and is expressed in gonadal somatic cells. In some nonmammalian species, fshr expression is much higher in the ovary than in the testis during gonadal sex differentiation, suggesting that FSHR is involved in ovarian development in nonmammalian vertebrates. However, little is known of FSHR knockout phenotypes in these species. Here we screened for fshr mutations by a medaka (Oryzias latipes) target-induced local lesion in the genomes and identified one nonsense mutation located in the BXXBB motif, which is involved in G protein activation. Next, we used an in vitro reporter gene assay to demonstrate that this mutation prevents FSHR function. We then analyzed the phenotypes of fshr mutant medaka. The fshr mutant male medaka displayed normal testes and were fertile, whereas the mutant female fish displayed small ovaries and were infertile because vitellogenesis was inhibited. The mutant females also have suppressed expression of ovary-type aromatase (cyp19a1a), a steroidogenic enzyme responsible for the conversion of androgens to estrogens, resulting in decreased 17β-estradiol levels. Moreover, loss of FSHR function caused female-to-male sex reversal in some cases. In addition, the transgenic overexpression of fshr in fshr mutants rescued FSHR function. These findings strongly suggest that in the medaka, FSH regulates the ovarian development and the maintenance mainly by the elevation of estrogen levels. We present the first FSHR knockout phenotype in a nonmammalian species.

Localization of apoptotic and proliferating cells and mRNA expression of caspases and Bcl-2 in gonads of chicken embryos

The aim of the present study was to analyze participation of apoptosis and proliferation in gonadal development in the chicken embryo by: (1) localization of apoptotic (TUNEL) and proliferating (PCNA immunoassay) cells in male and female gonads and (2) examination of mRNA expression (RT-PCR) of caspase-3, caspase-6 and Bcl-2 in the ovary and testis during the second half of embryogenesis and in newly hatched chickens. Apoptotic cells were found in gonads of both sexes. At E18 the percentage of apoptotic cells (the apoptotic index, AI) in the ovarian medulla and the testis was lower (p<0.05) than in the ovarian cortex. In the ovarian medulla, the AI at E18 was lower (p<0.05) than on E12. In the testis, the AI was significantly lower (p<0.05) at E18 than at E15 and 1D. The percentage of proliferating cells (the proliferation index: PI) within the ovary significantly increased from E15 to 1D in the cortex, while proliferating cells in the medulla were detected only at E15. In the testis, the PI gradually increased from E12 to 1D. The mRNA expression of caspase-3 and -6 as well as Bcl-2 was detected in male and female gonads at days 12 (E12), 15 (E15) and 18 (E18) of embryogenesis and the day after hatching (1D). The expression of all analyzed genes on E12 was significantly higher (p<0.05) in female than in male gonads. This difference was also observed at E15 and E18, but only for the caspase-6. The results obtained showed tissue- and sex-dependent differences in the number of apoptotic and proliferating cells as well as mRNA expression of caspase-3, -6 and Bcl-2 genes in the gonads of chicken embryos. Significant increase in the number of proliferating cells in the ovarian cortex and lack of these cells in the ovarian medulla (stages E12, E18, 1D) simultaneous with decrease in the intensity of apoptosis only in the medulla indicates that proliferation is the dominant process involved in the cortical development, which constitutes the majority of the functional structure of the fully developed ovary. No pronounced changes in the expression of apoptosis-related genes found during embryogenesis suggest that they cannot be considered as important indicators of gonad development. The molecular mechanisms of the regulation of balance between apoptosis and proliferation in developing avian gonads need to be further investigated.

Effect of luteinizing hormone on the right regressing ovary of newly hatched chicks treated during embryonic development

We studied the histologic and stereological changes induced in the right ovary of newly hatched chicks treated with LH during their embryonic development. Results indicate that LH administration causes a diminution in size and total volume (P < 0.01) of the right ovary, as well as a decrease in the total volume of lacunar channels, blood vessels, and interstitium. Other changes obtained after LH treatment were a reduction (P < 0.001) in the number of germ cells, as well as an increase in the total volume of interstitial cell cords (P < 0.01). This expansion is due to the increase of cellular volume of interstitial cells (P < 0.001) and not to their number, which decrease in the LH-treated right ovary. All these modifications were similar to those occurring in the regressing right ovary during development. The findings suggest that the right ovary of the newly hatched chick is able to respond to LH treatment during embryonic development, inducing marked histologic changes that accelerate its regression.

Molecular characterization and identification of a novel polymorphism of 200 bp indel associated with age at first egg of the promoter region in chicken follicle-stimulating hormone receptor (FSHR) gene

Follicle-stimulating hormone receptor (FSHR) plays an important role in animal follicular development. Polymorphisms in FSHR promoter region likely impact transcription and follicle growth and maturation. In this study, a fragment of ~1.9 kb of cFSHR promoter for Zang, Xianju, Lohmann Brown, Jining Bairi and Wenchang breeds (line) was obtained. Totally 49 variations were revealed, of which 39 are single nucleotide substitutions, one is nucleotide substitution of (TTG) to (CAC) and nine are indels. Polymorphism at -874 site (a 200 bp indel mutation) was identified, and their effects on egg production traits as well as gene expression were analyzed. At this site, allele I(+) was dominant in Lohmann Brown and Xinyang Brown (a synthetic egg-laying line) lines, but very rare in three Chinese indigenous chicken breeds, namely Jining Bairi, Wenchang, Zang and one synthetic boiler line (Luqin). In Xinyang Brown population, the polymorphism was associated with age at first egg (AFE) (P < 0.05) and its effect on egg number at 37 weeks of age (E37) and egg number at 57 weeks of age (E57) was not significantly different (P > 0.05). The cFSHR mRNA level was not significantly different between three genotypes in small white and small yellow follicles of Xinyang Brown hens, however, allele I(+) tends to increase cFSHR transcription.

Ontogenic characterization of gene expression in the developing neuroendocrine system of the chick

The neuroendocrine system consists of five major hypothalamic-pituitary hormone axes that regulate several important metabolic processes, and it develops in all vertebrates during embryogenesis. In order to define initiation and establishment of these five axes, mRNA expression profiles of hypothalamic releasing and release-inhibiting factors, their pituitary receptors, and pituitary hormones were characterized during the second half of embryogenesis and first week post-hatch in the chick. Axis initiation was defined as the age when pituitary hormone mRNA levels began to increase substantially, and establishment was defined as the age when mRNA for all components had reached maximum expression levels. The adrenocorticotropic axis appears established by e12, as there were no major increases in gene expression after that age. Hypothalamic thyrotropin-releasing hormone and pituitary thyroid-stimulating hormone β-subunit increased between e10 and e18, indicating establishment of the thyrotropic axis during this period. Pituitary growth hormone substantially increased on e16, and hypothalamic growth hormone-releasing hormone did not increase until e20, indicating that somatotropic axis activity is established late in embryonic development. Lactotropic axis initiation is evident just prior to hatch, as pituitary prolactin and vasoactive intestinal peptide receptor 1 did not increase until e18 and e20, respectively. Hypothalamic gonadotropin-releasing hormone 1 increased after hatch, and pituitary luteinizing hormone β-subunit expression remained low until d3, indicating the gonadotropic axis is not fully functional until after hatching. This study is the first to characterize major hypothalamic and pituitary components of all five neuroendocrine axes simultaneously and considerably increases our understanding of neuroendocrine system establishment during development.