Gonadotropins regulate ovarian germ cell mitosis/meiosis decision in the embryonic chicken

The effects of endogenous FSH and its receptor on oogenesis and folliculogenesis in female Alligator sinensis

BACKGROUND

The precise mechanisms of hormone action responsible for the full course of events modulating folliculogenesis in crocodilian have not been determined, although histological features have been identified.

RESULTS

The Alligator sinensis ovarian morphological characteristics observed at 1, 15, 30, 60, 90, and 300 days post hatching(dph) revealed that the dynamic changes in germ cells varied in different meiotic and developmental stages, confirming that the processes of folliculogenesis were protracted and asynchronous. The presence of endogenous follicle-stimulating hormone(FSH) mRNA and protein expression within the cerebrum at 1 dph, in parallel with the increase in germ cells within the germ cell nests(Nest) from 1 dph to 15 dph, suggested that endocrine regulation of the pituitary-gonad axis is an early event in oogonia division. Furthermore, the endogenous expression of FSH showed a trend of negative feedback augmentation accompanied by the exhaustion of maternal yolk E₂ observed at 15 dph. Such significant elevation of endogenous FSH levels was observed to be related to pivotal events in the transition from mitosis to meiosis, as reflected by the proportion of oogonia during premeiosis interphase, with endogenous FSH levels reaching a peak at the earliest time step of 1 dph. In addition, the simultaneous upregulation of premeiotic marker STRA8 mRNA expression and the increase in endogenous FSH further verified the above speculation. The strongly FSHr-positive label in the oocytes within Pre-previtellogenic follicles was synchronized with the significant elevation of ovarian cAMP detected at 300 dph, which suggested that diplotene arrest maintenance during early vitellogenesis might be FSH dependent. In addition, preferential selection in asynchronous meiotic initiation has been supposed to act on somatic supportive cells and not directly on germ cells via regulation of FSH that in turn affects downstream estrogen levels. This suggestion was verified by the reciprocal stimulating effect of FSH and E₂ on the accelerated meiotic marker SYCP3 and by the inhibited cell apoptosis demonstrated in ovarian cell culture in vitro.

CONCLUSION

The corresponding results contribute an expansion of the understanding of physiological processes and shed some light on the specific factors responsible for gonadotropin function in the early folliculogenesis of crocodilians.

LIF and bFGF enhanced chicken primordial follicle activation by Wnt/β-catenin pathway

The cytokines leukemia inhibitory factor (LIF) and basic fibroblast growth factor (bFGF) are closely related to the development of primordial follicles. In this study, the functions and correlation of LIF and bFGF in the development of chicken primordial follicles were examined, along with the signaling pathways including protein kinase B (AKT), extracellular regulated protein kinase (ERK) and Wnt/β-catenin signaling pathways. Ovarian tissues were collected from four-day-old chicks and incubated with LIF and bFGF alone or in combination for three days to observe the changes in follicular development. Results showed that there was a time-dependent correlation between the changes in expression of LIF/its receptor (LIFR) and the developmental process of primordial follicles. LIF and bFGF exerted a synergistic effect on the activation of primordial follicles. However, SC144 (an antagonist of LIFR) inhibited this stimulating action. The effect by LIF and bFGF were shown to operate at AKT and ERK signaling pathways to suppress cell apoptosis and promote proliferation (P < 0.05) via the Wnt/β-catenin signaling (P < 0.05). In conclusion, local cytokines LIF and bFGF functioned to enhance the activation of chicken primordial follicles by increasing cell proliferation and decreasing apoptosis in the ovary involving AKT, ERK and Wnt/β-catenin signaling.

Stem Cells in Adult Mice Ovaries Form Germ Cell Nests, Undergo Meiosis, Neo-oogenesis and Follicle Assembly on Regular Basis During Estrus Cycle

Very small embryonic-like (VSELs) and ovarian (OSCs) stem cells are located in adult mammalian ovary surface epithelium (OSE). OSCs can expand long-term and differentiate into oocyte-like structures in vitro and have resulted in birth of fertile pups. Lineage tracing studies have provided evidence to suggest OSCs differentiation into oocytes in vivo. But how these stem cells function under normal physiological conditions has not yet been well worked out. Besides studying STRA-8 and SCP-3 expression in enzymatically isolated OSE cells smears, mice were injected BrdU to track mitosis, meiosis and follicle assembly. H&E stained OSE cells during late diestrus and proestrus showed VSELs undergoing asymmetrical cell divisions to give rise to slightly bigger OSCs which in turn underwent symmetrical cell divisions followed by clonal expansion (rapid expansion with incomplete cytokinesis) during early estrus to form germ cell nests (GCN). OCT-4, SSEA-1, MVH and DAZL positive cells in GCN expressed Erα, Erβ and FSHR, were interconnected by ring canals (TEX-14), showed mitochondrial aggregation (Cytochrome C) and Balbiani Body (TRAL). Apoptosis in 'nurse' cells was marked by PARP and putative oocytes were clearly visualized. BrdU was detected in cells undergoing mitosis/meiosis and also in an oocyte of secondary follicle. FACS sorted, green fluorescent protein (GFP) positive VSELs upon transplantation resulted in GFP positive GCN suggesting crucial role for VSELs in adult ovaries. Results suggest that various events described during oogenesis and follicle assembly in fetal ovaries are recapitulated on regular basis in adult ovary and result in the formation of follicles.

Leptin Modulates the mRNA Expression of Follicle Development Markers in Post-hatch Chicks in an Age-Dependent Manner

Leptin is involved in regulating reproductive function in chickens, and the development of the leptin system is initiated during the early embryonic stage; however, whether leptin has a specific role in regulating the ovarian development in early post-hatch days is still not fully understood. This study investigated the expression of ovarian functional markers in growing juvenile chickens, along with the effects of leptin on gene expression in the hypothalamus–pituitary–gonadal (HPG) axis on specific ovarian-remodeling days. Leptin receptor (LEPR), follicle-stimulating hormone receptor (FSHR), and the mRNA expression of aromatase (CYP19A1) tended to increase with age in the ovaries of growing chicks. In the ovaries of 7-day-old chicks, intraperitoneally injected leptin significantly increased the mRNA expressions of LEPR, FSHR, and CYP19A1, and this resulted in the increased serum estradiol levels. However, leptin had no effect on hypothalamic LEPR, gonadotropin-releasing hormone 1 (GnRH1), or gonadotropin-inhibitory hormone (GnIH) mRNAs; however, in the pituitary gland, leptin significantly increased the mRNA expression of luteinizing hormone beta subunit (LHB) but had no effect on the mRNA expression of follicle-stimulating hormone beta subunit (FSHB). In 28-day-old chicks, hypothalamic and pituitary mRNAs were unaffected by leptin administration, except hypothalamic LEPR mRNA that was upregulated by a high dose of leptin. In the ovary, leptin dose-dependently decreased the mRNA expression of LEPR; low doses of leptin significantly increased the mRNA expression of FSHR, whereas high doses significantly decreased this expression; leptin did not affect the mRNA expression of CYP19A1; and high leptin doses significantly reduced the serum estradiol levels. Collectively, the results of this study show that leptin modulates ovarian development and folliculogenesis marker genes by primarily acting on ovaries on the specific ovarian-remodeling days in post-hatch chicks, which may alter folliculogenesis and ovarian development toward puberty in chicken.

Reproductive aspects of Japanese quails (Coturnix coturnix japonica) hatched from eggs incubated under different light colors

The objective of this study was to evaluate the effect of exposure to different colors of light during egg incubation on the reproductive parameters of male and female Japanese quails. A total of 1776 eggs were incubated under four lighting conditions for 24 h a day during the entire incubation period: white LEDs, green LEDs, red LEDs and darkness (control). The experimental design was a randomized block (incubation time) with four treatments of six replicates of two cages each. After hatching, the birds were housed in brood cages with 18 birds each to 35 days of age, when they were sexed and transferred to production cages for evaluation of reproductive parameters. After the onset of laying, the number of eggs in each cage was recorded daily, and the values were used to obtain the age of the females at first egg and at 80% laying. At 35 and 60 days of age, several birds from each cage were euthanized for anatomical and histological evaluation of the gonads. Two females from each cage were weighed every three days until 60 days of age to determine the growth curve. After 60 days, eggs from each cage were collected and assessed for external and internal quality. At 70, 74 and 78 days of age, semen collection was performed and seminal quality was evaluated. Then, the males were transferred to cages containing 9 females for the fertility test. Hatchability was higher (P < 0.05) in eggs incubated in the dark and under the red LED. The age of maximum growth was higher (P < 0.05) in birds from eggs incubated in the dark and under the white LED. There was no difference (P > 0.05) in the anatomical and histological characteristics of the testicles between the groups incubated under different light colors, except for the diameter of the seminiferous tubules, which was greater (P = 0.05) in the dark and in the white LED groups. There was no effect (P > 0.05) of light color during incubation on the productive index or egg quality of adult birds. There was also no effect (P > 0.05) on sperm quality, except for sperm motility, the values of which were higher (P < 0.05) in birds from eggs incubated in different colors of light. However, this difference was not sufficient to significantly (P > 0.05) influence bird fertility. It is concluded that under the studied conditions, the incubation of quail eggs under white, red, and green LED lamps does not influence the reproductive characteristics of the quails.

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.

Enhancing effect of FSH on follicular development through yolk formation and deposition in the low-yield laying chickens

Healthy and efficient development of ovarian follicles largely determines poultry laying performance. In low-yield laying chickens, retarded follicle progression resulted in decreased prehierarchical follicles. In this study the extenuating effect of follicle-stimulating hormone (FSH) on delayed follicular development was investigated in the low-yield chickens. Results showed that FSH administration in vivo accelerated development of prehierarchical follicles, with increased expression of steroidogenic enzymes and follicular angiogenesis through elevating plasma levels of 17β-estradiol, progesterone, luteinizing hormone and the expression of vascular endothelial growth factor and its receptor as well as angiopoietins. Furthermore, treatment with FSH raised expression of lipid uptake and adipogenesis-related proteins and decreased tight junctions between granulosa cells. Meanwhile, the results of the in vivo studies were confirmed by the in vitro studies as FSH promoted development of the cultured prehierarchical follicles with increased angiogenesis, cell proliferation, steroid hormones synthesis and yolk deposition. These results indicated FSH enhanced follicular development in the low-yield laying chickens involving increased follicular angiogenesis.

Estimation of dietary manganese requirement for laying duck breeders: effects on productive and reproductive performance, egg quality, tibial characteristics, and serum biochemical and antioxidant indices

This study was aimed at estimating the dietary manganese (Mn) requirement for laying duck breeders. A total of 504 Longyan duck breeders (body weight: 1.20 ± 0.02 kg) aged 17 wk were randomly allocated to 6 treatments. The birds were fed with a basal diet (Mn, 17.5 mg/kg) or diets supplemented with 20, 40, 80, 120, or 160 mg/kg of Mn (as MnSO₄·H₂O) for 18 wk. Each treatment had 6 replicates of 14 ducks each. As a result of this study, dietary Mn supplementation did not affect the productive performance of laying duck breeders in the early laying period (17–18 wk), but affected egg production, egg mass, and feed conversion ratio (FCR) from 19 to 34 wk (P < 0.05), and there was a linear and quadratic effect of supplement level (P < 0.05). The proportion of preovulatory ovarian follicles increased (P < 0.01) linearly and quadratically, and atretic follicles (weight and percentage) decreased (P < 0.05) quadratically with dietary Mn supplementation. The density and breaking strength of tibias increased (quadratic; P < 0.05), the calcium content of tibias decreased (linear, quadratic; P < 0.01), and Mn content increased (linear, quadratic; P < 0.001) with increase in Mn. The addition of Mn had a quadratic effect on serum contents of estradiol, prolactin, progesterone, luteinizing hormone, and follicle-stimulating hormone (P < 0.001). Dietary Mn supplementation decreased serum contents of total protein (linear, P < 0.05), glucose (quadratic, P < 0.05), total bilirubin, triglycerides, total cholesterol, low-density lipoprotein cholesterol, and calcium (linear, quadratic; P < 0.05). The serum total antioxidant capacity and total and Mn-containing superoxide dismutase activities increased (linear, quadratic; P < 0.001), and malondialdehyde content decreased (linear, quadratic; P < 0.001) in response to Mn supplemental levels. The dietary Mn requirements, in milligram per kilogram for a basal diet containing 17.5 mg/kg of Mn, for Longyan duck breeders from 19 to 34 wk of age were estimated to be 84.2 for optimizing egg production, 85.8 for egg mass, and 95.0 for FCR. Overall, dietary Mn supplementation, up to 160 mg/kg of feed, affected productive performance, tibial characteristics, and serum biochemical and antioxidant status of layer duck breeders. Supplementing this basal diet (17.5 mg/kg of Mn) with 85 to 95 mg/kg of additional Mn was adequate for laying duck breeders during the laying period.

Effect of dietary N-carbamylglutamate on development of ovarian follicles via enhanced angiogenesis in the chicken

N-carbamylglutamate (NCG), an analogue of N-acetyl-L-glutamate (NAG), can increase arginine synthesis in mammals and improve the reproductive performance. However, the effect of NCG on poultry laying performance is still unclear. This study investigated the effect of dietary NCG on development of chicken ovarian follicles. The dosage and timing for NCG administration were evaluated for its effect on follicular development. Results showed that supplementation with 1% NCG in the diet for 14 D led to accelerated development of growing follicles (over 60 μm in oocyte diameter) and significantly increased feed intake and feed efficiency. Plasma amino acids (AA) analysis showed that feeding with 1% NCG significantly increased of plasma AA levels. RNA-seq analysis revealed that NCG supplementation upregulated expression of genes related to angiogenesis and cell proliferation, but downregulated expression of apoptosis-related genes. Meanwhile, RT-qPCR and Western blot analysis validated the RNA-seq results. Moreover, NCG enhanced plasma NO level; upregulated expression of PKG-I, Raf1, and p-p38; and increased angiogenesis of the ovaries. In conclusion, dietary NCG (1% for 14 D) can promote development of ovarian follicles by increasing angiogenesis in ovaries of the chicken.

TGF-β1 sustains germ cell cyst reservoir via restraining follicle formation in the chicken

The transforming growth factor β (TGF-β) superfamily members are important molecules that regulate many ovarian functions under normal physiological and pathological conditions. TGF-β1 and its receptors are highly expressed in the ovarian cells of many species. However, the effect of TGF-β1 on the capacity of the avian germ cell reservoir remains unknown. In this study, 5-day-old chicks were injected with TGF-β1 (2.5, 12.5, and 62.5 μg/kg body weight) for 3 days to assess the effect of TGF-β1 on early follicle development. Morphological analysis showed that treatment with TGF-β1 (12.5 μg/kg) increased the number of germ cell cysts and reduced the number of primordial and growing follicles. The diameter and area of oocytes and follicles were decreased after TGF-β1 treatment. Immunohistochemical staining of the proliferating cell nuclear antigen revealed that the ratios of the positive somatic and granulosa cells were decreased by 16.2% and 2.48%, respectively. Furthermore, more apoptotic cells were observed in the TGF-β1 group than those of the control by terminal deoxynucleotidyl transferase dUTP nick end labeling assay. In addition, we cultured the 5d chicken ovaries for 3 days in vitro and found that treatment with TGF-β1 (10 ng/mL) manifested similar results as the in vivo experiment. However, the negative effect of TGF-β1 on early ovary development was rescued by treatment with a TGF-βR1 inhibitor SD208, resulting in increased expression of steroidogenic enzymes and cell cycle-regulating proteins. In conclusion, TGF-β1 could maintain the germ cell reservoir by restraining follicle activation involving reduced cell proliferation and steroidogenic enzymes gene expression at the early stage of ovarian development.

Coherent apoptotic and autophagic activities involved in regression of chicken postovulatory follicles

After ovulation in mammals, rupture of mature follicles is reorganized into the corpus luteum that secrets progesterone (P₄) to stimulate endometrial development. The situation in birds differs considerably. Beyond ovulation the ruptured avian follicle forms a postovulatory follicle (POF) that is not considered analogous to mammalian corpus luteum. The function and regression mechanisms of avian POFs remain poorly understood. Here we investigated the changes in apoptotic and autophagic activities that were involved during POF degradation. Results showed that the structure and secretory function of POF3 manifested the most apparent deterioration during whole processes of regression. A TUENL assay revealed that the granulosa layer maintained longer viability than the theca layer. Importantly, mitochondrial apoptosis and endoplasmic reticulum (ER) stress-associated genes and proteins reached their highest levels in the granulosa cells of POF3. Beclin1 was distributed mainly in theca cells and coupled with LC3β-II accumulation, Sequestosome-1 (p62) degradation and Beclin1 elevation confirmed that autophagic activity had increased dramatically in the theca layer of POFs. These results indicate that the apoptosis of the granulosa cells from POFs occurs by mitochondrial apoptosis and ER stress and that a coherence of Beclin1-induced autophagy and caspase-induced apoptosis results in regression of theca layers of avian POFs.

Reciprocal stimulating effects of bFGF and FSH on chicken primordial follicle activation through AKT and ERK pathway

Basic fibroblast growth factor (bFGF) and follicle-stimulating hormone (FSH) both play important roles in primordial follicle development. Here we investigated the reciprocal stimulation effects of a cytokine bFGF and FSH on primordial follicle development in the chicken and considered a possible signaling mechanism involving protein kinase B (AKT) and extracellular regulated protein kinase (ERK) pathways. 4-day-old chicken ovaries were treated with bFGF and FSH for 3 days in culture to investigate the effects of bFGF and FSH on primordial follicle development. Methods included HE staining, immunohistochemistry, quantitate real-time PCR, Western blot and immunofluorescence. A correlated change of bFGF receptor (FGFR1) mRNA expression and time course of primordial follicle activation was revealed in the early chick ovaries. A reciprocal stimulation effect on primordial follicle activation was demonstrated for bFGF and FSH, along with accelerated granulosa cells proliferation and decreased cell apoptosis. The promoting effect of bFGF was attenuated by the FGFR1 inhibitor SU5402 where the percentage of growing follicles had decreased. AKT and ERK signaling pathways mediated the action of bFGF and FSH in their promotion of primordial follicle activation. Cytokine bFGF and FSH imposed reciprocal stimulating effects on granulosa cell proliferation and anti-apoptosis to promote primordial follicle activation via the PI3K-AKT and ERK signaling pathways in early chick ovaries.

Interaction of Follicle-Stimulating Hormone and Stem Cell Factor to Promote Primordial Follicle Assembly in the Chicken

Follicle-stimulating hormone (FSH) and KIT signaling are required for ovarian development. In this study the interactive effect of FSH and stem cell factor (SCF) on folliculogenesis was investigated in the chicken. Correlated changes between the FSH receptor and the expression of KIT signaling genes were seen to be involved in the formation of the chicken primordial follicles. Follicle-stimulating hormone and SCF displayed a reciprocal stimulating effect in the promotion of folliculogenesis involving elevated phosphorylation of mitogen-activated protein kinases (MAPK) and protein kinase B (AKT) proteins. Knockdown of c-KIT or SCF reduced the stimulatory effect of FSH on KIT signaling as well as upon MAPK and AKT phosphorylation. Treatment of FSH and SCF in combination enhanced ovarian cell proliferation and N-cadherin expression, but inhibited cell apoptosis and E-cadherin expression. Overall, the reciprocal stimulating effect of FSH and SCF in promoting chicken follicle assembly involving accelerated ovarian cell proliferation, N-cadherin expression, inhibited cell apoptosis, and E-cadherin expression is demonstrated.

Promotion of the prehierarchical follicle growth by postovulatory follicles involving PGE2 -EP2 signaling in chickens

The postovulatory follicle (POF) in birds is an enigmatic structure, the function of which remains largely unknown. Previous studies on chickens have shown that removal of POFs leads to the postponement of oviposition and the disturbance of broody behavior. One suggestion is that POFs may secrete some crucial hormones or cytokines to act on reproductive organs. However, such secretions and their specific target organs remain to be identified. Here, we investigate the putative functions of POFs in promoting the development of prehierarchical follicles in chickens and explore the possible signaling mechanisms controlling these processes. Results show that POFs express steroidogenic acute regulatory protein (STAR), cholesterol side-chain cleavage enzyme (CYP11A1), cyclooxygenase 1 (COX1), and COX2 in granulosa cells (GCs), and, most notably, that POF1 produces more prostaglandin E2 (PGE₂ ) or prostaglandin F2α than do the F1 follicle or the other POFs. Using coculture systems, we also found that POF1 or GCs from POF1 (POF1-GCs) significantly promote the proliferation of theca externa cells of small white follicles (SWFs, one phase of the prehierarchical follicle). Treatment with PGE₂ significantly facilitates theca externa cell proliferation in SWFs. This POF-stimulating effect on SWF growth was prevented by treatment with indomethacin (COX inhibitor) or TG6-10-1 (PGE₂ type 2 receptor [EP2] antagonist). Therefore, POF1 may secrete PGE₂ to stimulate the progression of SWF by PGE₂ -EP2 signaling. These results indicate that POF1 may serve as a transient supplementary endocrine gland in the chicken ovary that stimulates the development of the prehierarchical follicles through PGE₂ -EP2 signaling.

Molecular regulation of follicle-stimulating hormone synthesis, secretion and action

Follicle-stimulating hormone (FSH) plays fundamental roles in male and female fertility. FSH is a heterodimeric glycoprotein expressed by gonadotrophs in the anterior pituitary. The hormone-specific FSHβ-subunit is non-covalently associated with the common α-subunit that is also present in the luteinizing hormone (LH), another gonadotrophic hormone secreted by gonadotrophs and thyroid-stimulating hormone (TSH) secreted by thyrotrophs. Several decades of research led to the purification, structural characterization and physiological regulation of FSH in a variety of species including humans. With the advent of molecular tools, availability of immortalized gonadotroph cell lines and genetically modified mouse models, our knowledge on molecular mechanisms of FSH regulation has tremendously expanded. Several key players that regulate FSH synthesis, sorting, secretion and action in gonads and extragonadal tissues have been identified in a physiological setting. Novel post-transcriptional and post-translational regulatory mechanisms have also been identified that provide additional layers of regulation mediating FSH homeostasis. Recombinant human FSH analogs hold promise for a variety of clinical applications, whereas blocking antibodies against FSH may prove efficacious for preventing age-dependent bone loss and adiposity. It is anticipated that several exciting new discoveries uncovering all aspects of FSH biology will soon be forthcoming.

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.

Novel genes and hormonal regulation for gonadal development during embryogenesis in chickens

Asymmetrical gonadal morphogenesis is well known in female chickens in contrast to males where both gonads develop symmetrically. However, only a few genes have been reported to determine differential morphology between female and male gonads in chicken and their mechanisms of action are unclear. Therefore, we focused on three genes (TOM1L1, TTR, and ZEB1) that are related to cellular proliferation and embryonic development based on previous study indicating up- or down-regulated transcripts in the asymmetric female gonads between embryonic day 6 (E6) and E9 by microarray analyses. To define the validity of the gene expression pattern discovered, q-PCR and in situ hybridization analyses were performed. In the left female gonad between E6 and E9 the expression of TOM1L1, TTR and ZEB1 increased at E9. On the other hand, TOM1L1 and TTR increased significantly in both male gonads between E6 and E9. In addition, recombinant FSH and LH stimulated proliferation of gonadal cells and influenced expression of selected genes in chickens. This suggests that hormonal regulation is involved in growth and development in the embryonic gonad of chickens. Collectively, the results show differential gene expression between the left and right gonads in chicken embryos and that of is regulated by gonadotropin. These results provide novel insights into candidate genes regulating gonad development and differentiation.

Progesterone regulates chicken embryonic germ cell meiotic initiation independent of retinoic acid signaling

The signaling molecule retinoic acid (RA) is known to trigger germ cells to enter meiosis. However, RA may not be the only secreted inducer of meiosis. Our previous data indicate that luteinizing hormone also promotes germ cell meiotic initiation by upregulating 3βHSDII transcription. Here, using chicken embryos, we investigate the role of progesterone (P4) in regulating germ cell meiotic initiation. Progesterone treatment at embryonic Day 9.5 accelerated germ cell meiosis entry in the female chicken embryos. However, P4 treatment in vivo did no influence on testicular germ cells but triggered their meiotic initiation in the cultured testes. As treatment with an RA receptor (RAR) inhibitor did not block the stimulatory effect of P4 on germ cell meiotic initiation, this P4 stimulatory effect seems to be independent of RAR-mediated signaling. The abundance of RA metabolism-related enzymes and RAR (RARβ) mRNAs did not differ significantly between P4-treated and control individuals. The RA concentration in the ovaries remained unchanged by P4 treatment in vivo. Because no inhibition by the P4 receptor (PR) nuclear receptor antagonist mifepristone on P4 effect was observed in either in vitro or in vivo experiments, the effect of P4 on germ cell meiotic initiation is probably mediated by membrane PRs (mPR). The mPRα, mPRβ, and mPRγ mRNAs were all expressed in the embryonic ovaries. The expression of mPRα and mPRβ was higher than that of mPRγ. Immunohistochemical results showed that mPRα-positive cells were mainly scattered in the ovarian cortex area where most germ cells were distributed. The mPRβ-positive cells were widely distributed in the ovaries, and positive cells were clustered with a similar morphology to that of germ cell clusters. In conclusion, P4 may regulate embryonic germ cell meiotic initiation independent of RA signaling through the membrane PRs. This study provides a new insight into the mechanisms of germ cell meiotic initiation in the chicken.