Bone morphogenetic protein-6 enhances gonadotrophin-dependent progesterone and inhibin secretion and expression of mRNA transcripts encoding gonadotrophin receptors and inhibin/activin subunits in chicken granulosa cells

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.

Discovery of single nucleotide polymorphisms in bone morphogenetic protein (BMP) genes of goats by double digest restriction-site associated DNA sequencing

Context Two native goat breeds from Kerala, Malabari and Attappady Black, differ significantly in prolificacy (i.e. no. of kids born/kidding). Prolificacy is an important economic trait and the subject of genetic research showing that bone morphogenetic protein (BMP) genes have a significant effect. Double digest restriction-site associated DNA sequencing (ddRADseq) is a highly efficient and low cost technology for high density discovery of single nucleotide polymorphisms (SNPs), which could serve as predictive markers for animal breeding programs. Aims The study was aimed at discovering SNPs in BMP genes that affect prolificacy, using ddRADseq followed by validation of selected SNP. Methods Blood DNA samples of 10 highly prolific Malabari and 10 less prolific Attappady Black goats were pooled by group and subjected to ddRADseq. SNPs observed in BMP genes were investigated and compared between groups. A validation study was done for the c.614–32789C&gt;T variant in 100 Malabari and 50 Attappady Black goats by using PCR-RFLP. Key results In total, 6333 variants were identified by ddRADseq. Three variants were identified in BMP genes, which included two intronic variants c.614–32789C&gt;T and c.490+6793T&gt;C, in genes BMP6 and BMP5 and a downstream gene variant near the BMPR1B gene. According to ddRADseq data, variants in BMP5 and BMP6 differed in allelic distribution between Malabari and Attappady Black goats. For c.490+6793T&gt;C in BMP5, the CC genotype was predominant in the highly prolific Malabari whereas TC was present in the Attappady Black group. The variant c.614–32789C&gt;T in BMP6 was genotyped as TC in Malabari and CC in Attappady Black goats by ddRADseq. This variant was predicted to have an effect on splicing, according to the tool SplicePort. On the basis of bioinformatics analysis and the role of BMP6 gene in follicular dynamics, the variant in BMP6 was selected for further validation studies. All three genotypes were identified by PCR-RFLP; the C allele was the rare allele in the population with an allele frequency of 0.36. Presence of both alleles C and T and the three genotypes CC, TC and TT in this larger population substantiated the robustness of ddRADseq technique. Conclusions The technique discovered high confidence SNPs, which could be used for further validation and association studies to develop markers for selection of animals and for genetic improvement of this complex trait. Implications Techniques such as ddRADseq provide a large number of SNPs, and investigation of those polymorphisms found across the genome will help to identify new loci affecting traits of interest. This, in turn, will aid in exploring genetically complex traits in a faster and cheaper manner.

Co-culture model reveals the characteristics of theca cells and the effect of granulosa cells on theca cells at different stages of follicular development

Theca cells (TCs) play an important role in follicular development, which cannot be separated from granulosa cells (GCs). However, compared with mammals, the TCs and the effects of GCs on TCs at different follicular development stages (FDSs) have specific characteristics in avian species, but none of them have been clearly defined. In this study, we established an in vitro co-culture (with GC at the corresponding stage) model of goose TCs at different FDSs (pre-hierarchical, hierarchical and F1) by using a transwell system. The properties of TCs in co-culture at the three FDSs, including cell morphology, activity and intracellular lipid content, as well as the expression of key genes involved in de novo lipogenesis, steroidogenesis, proliferation and apoptosis, were examined and defined. We further compared the mono-culture and co-culture groups. After co-culture, the activity of TCs showed significant (p < .01) increases in all stages; moreover, in pre-hierarchical TCs, the expression levels of FAS, SREBP, 3β-HSD and CCND1 were promoted, and PPARγ, CYP19, BCL2 and CAS3 were inhibited (p < .05); in the hierarchical TCs, the expression levels of PPARγ, FAS, CYP19, CCND1 and BCL2 were promoted, and SREBP, STAR, 3β-HSD and CAS3 were inhibited (p < .05), whereas in the F1 TCs, the expression levels of PPARγ, FAS, 3β-HSD, CYP19 and CCND1 were promoted, and STAR and CAS3 were inhibited (p < .05). These results suggested that GCs at the three FDSs have dynamic and complex influences on the physiological characteristics of TCs, and the influences on TCs at the three FDSs were varied.

Reproductive management of poultry

Based on data from the UN's Food and Agricultural Organization, about 120 million metric tons of poultry meat were produced globally in 2016. In addition, about 82 million metric tons of eggs were produced. One of the bases for this production is the reproductive efficiency of today's poultry. This, in turn, is due to their inherent reproductive physiology, intensive genetic selection and advances in husbandry/management. The system of reproduction in males in largely similar to that in mammals except that there is no descent of testes. In females, there are marked differences with there being a single ovary and oviduct; the latter being the name of the differentiated entire Müllerian duct. Moreover, females produce eggs with a yolky oocyte surrounded by albumen, membranes and shell. Among the most successful reproductive management techniques are optimizing photoperiod, light intensity and nutrition. Widespread employment of these has allowed maximizing production. Laying hens can be re-cycled toward the end egg production. Other aspects of reproductive management in poultry include the following: artificial insemination (almost exclusively employed in turkeys) and approaches to reduce broodiness together with cage free (colony), conventional, enriched and free-range systems.

Implication of SLIT3-ROBO1/ROBO2 in granulosa cell proliferation, differentiation and follicle selection in the prehierarchical follicles of hen ovary

The SLIT/ROBO pathway has been implicated in prehierarchical follicular development of hen ovary by an intrafollicular autocrine and/or paracrine fashion. SLIT3, one of the key components of the SLIT/ROBO family, serves as a ligand that potentially interacts with the four receptors, ROBO1, ROBO2, ROBO3 and ROBO4. But the exact roles and regulatory mechanism of SLIT3 in chicken ovarian follicle development remain largely unclear. The present study was conducted to investigate the potential roles and molecular regulation of SLIT3 in granulosa cell (GC) proliferation, differentiation and follicle selection within the prehierarchical follicles of hen ovary. We found that SLIT3 interacts physically with the four ROBO receptors, but the expression of the ROBO1 and ROBO2 genes are more susceptible to the regulation of SLIT3 ligand than that of the ROBO3 and ROBO4 genes. Moreover, the siRNA-mediated knockdown of SLIT3 in the follicular GCs leads to a significant increase in cell proliferation. Conversely, overexpression of SLIT3 results in a remarkable reduction in GC proliferation. Furthermore, the overexpressed SLIT3 has notably decreased the mRNA and protein expression levels of follicle-stimulating hormone (FSHR), growth and differentiation factor 9 (GDF9), steroidogenic acute regulatory protein (STAR) and cytochrome P450 11A1 (CYP11A1) in the GCs. These results indicated that SLIT3 may play an inhibitory effect on GC proliferation, differentiation and follicle selection, and these suppressive actions of SLIT3 in the GC proliferation can be prohibited by the siRNA-mediated knockdown of ROBO1 and ROBO2 receptors. The current data provide a basis for further investigation of molecular mechanisms of SLIT3-ROBO1/2 pathway in controlling the prehierarchical follicle development of the hen ovary.

The effect of ovarian reserve and receptor signalling on granulosa cell apoptosis during human follicle development

The poor oocyte quality in older women has previously been linked to the depletion of the ovarian reserve of primordial follicles and an increase in granulosal apoptosis. Granulosa cells were collected from 198 follicles and individually analysed by flow cytometry. In the young IVF patients, the level of apoptosis was inversely proportional to the expression of bone morphogenetic protein (BMPR1B) and follicle stimulating hormone (FSH) receptors. Conversely, in the older patients this relationship became dysregulated. In the older patients, at the time of preovulatory maturation, the reduced apoptosis reflects the poor mitogenic growth turnover rate of healthy follicles rather than the death rate in an atretic follicle. Restoring an optimum receptor density and down-regulation of receptors may improve oocyte quality and the pregnancy rate in older women.

Enrichment of in vivo transcription data from dietary intervention studies with in vitro data provides improved insight into gene regulation mechanisms in the intestinal mucosa

Background

Gene expression profiles of intestinal mucosa of chickens and pigs fed over long-term periods (days/weeks) with a diet rich in rye and a diet supplemented with zinc, respectively, or of chickens after a one-day amoxicillin treatment of chickens, were recorded recently. Such dietary interventions are frequently used to modulate animal performance or therapeutically for monogastric livestock. In this study, changes in gene expression induced by these three interventions in cultured “Intestinal Porcine Epithelial Cells” (IPEC-J2) recorded after a short-term period of 2 and 6 hours, were compared to the in vivo gene expression profiles in order to evaluate the capability of this in vitro bioassay in predicting in vivo responses.

Methods

Lists of response genes were analysed with bioinformatics programs to identify common biological pathways induced in vivo as well as in vitro. Furthermore, overlapping genes and pathways were evaluated for possible involvement in the biological processes induced in vivo by datamining and consulting literature.

Results

For all three interventions, only a limited number of identical genes and a few common biological processes/pathways were found to be affected by the respective interventions. However, several enterocyte-specific regulatory and secreted effector proteins that responded in vitro could be related to processes regulated in vivo, i.e. processes related to mineral absorption, (epithelial) cell adherence and tight junction formation for zinc, microtubule and cytoskeleton integrity for amoxicillin, and cell-cycle progression and mucus production for rye.

Conclusions

Short-term gene expression responses to dietary interventions as measured in the in vitro bioassay have a low predictability for long-term responses as measured in the intestinal mucosa in vivo. The short-term responses of a set regulatory and effector genes, as measured in this bioassay, however, provided additional insight into how specific processes in piglets and broilers may be modulated by “early” signalling molecules produced by enterocytes. The relevance of this set of regulatory/effector genes and cognate biological processes for zinc deficiency and supplementation, gluten allergy (rye), and amoxicillin administration in humans is discussed.

Electronic supplementary material

The online version of this article (doi:10.1186/s12263-017-0559-1) contains supplementary material, which is available to authorized users.

Bone morphogenetic protein 15 may promote follicle selection in the hen

In the hen, optimal ovulation rate depends on selection of a single follicle into the pre-ovulatory hierarchy. Follicle selection is associated with increased oocyte growth and changes in gene expression in granulosa cells surrounding the oocyte, in preparation for ovulation. This study investigated the expression, function and regulation of bone morphogenetic protein-15 (BMP15) during follicle development in the hen. BMP15 mRNA expression was analyzed in the ooplasm and granulosa cells of 3mm follicles and was confirmed to be primarily in the ooplasm. BMP15 was detected by immunoblotting in 6 and 8mm follicles near the time of follicle selection. Expression of mRNA for BMP15 receptors (BMPR1B and BMPR2) in granulosa cells increased with follicle size, indicating that BMP15 may play an important role around follicle selection. The function of BMP15 was examined by culturing granulosa cells from 3-5mm and 6-8mm follicles with recombinant human BMP15 (rhBMP15). BMP15 increased expression of follicle stimulating hormone receptor (FSHR) mRNA and decreased anti-Müllerian hormone (AMH) mRNA and occludin (OCLN), factors associated with follicle maturation and growth in the hen. Hormonal regulation of BMP15 was assessed by whole follicle culture with estradiol (E2) which increased BMP15 mRNA expression. The distinct expression pattern of BMP15 and its receptors, coupled with the effects of BMP15 to increase FSHR mRNA and decrease AMH mRNA and OCLN mRNA and protein expression suggest that the oocyte may have a role in follicle selection in the chicken.

Characterization of bmp15 and its regulation by human chorionic gonadotropin in the follicle of gibel carp (Carassius auratus gibelio)

Bone morphogenetic protein (BMP15) is a member of the transforming growth factor β (TGF-β) superfamily with a key role in regulating follicle development in mammals and birds. However, potential ovarian roles of BMPs remain unexplored in teleosts. In this study, the full-length sequences of bmp15 were obtained using rapid-amplification of cDNA ends (RACE). The full-length cDNA sequence of bmp15 is 2217 bp which contained 214 bp 5'-UTR and 845 bp 3'-UTR. The open reading frame (ORF) sequence of bmp15 is 1158 bp, encoding a predicted protein of 385 amino acid residues. BMP15 has a specific RXXR protease cleavage site of TGF-β superfamily (is RIRR) and six conserved cysteine residues. Using real-time quantitative PCR revealed that bmp15 mRNA was largely expressed in the ovary and testis and mostly in oocytes within the follicle, slightly expressed in muscle, liver and pituitary. BMP15 is mainly present at stage I follicles by real-time quantitative PCR and immunohistochemistry. Phylogenetic analysis showed that gibel carp bmp15 was similar to bmp15 of zebrafish and other fish species. Treatment with human chorionic gonadotropin (hCG) in isolated follicles of gibel carp in vitro showed altered bmp15 mRNA expression: when treated with 10 ng/mL hCG for 10h, the expression level of bmp15 was significantly increased. However, with proceeding cultivation, the expression level of BMP15 mRNA decreased. The results of this study indicate that bmp15 may play a key role during development of follicles in gibel carp, especially in early stage follicles.

Differential regulation of gonadotropin receptors by bone morphogenetic proteins in the zebrafish ovary

Follicle-stimulating hormone receptor (fshr) and luteinizing hormone/choriogonadotropin receptor (lhcgr) exhibit differential temporal expression patterns during zebrafish folliculogenesis with fshr being dominant during vitellogenic growth and lhcgr increasing its expression dramatically before maturation. The dynamic and distinct expression patterns of fshr and lhcgr suggest that they are under tight regulatory control. However, the underlying mechanisms for the differential expression of the two receptors remain unknown. We have recently demonstrated that members of bone morphogenetic protein (BMP) family are largely expressed in the oocyte, while their receptors are exclusively localized on the follicle cells, suggesting a potential paracrine signaling from the oocyte to the follicle cells by BMPs. In this study, we investigated the effects of zebrafish BMP2b (zfBmp2b) and BMP4 (zfBmp4) on the expression of fshr and lhcgr using a novel co-culture approach. The recombinant zfBmp2b or zfBmp4-producing CHO cells were co-cultured with the zebrafish follicle cells followed by real-time qPCR analysis of fshr and lhcgr expression. Our results showed that zfBmp2b and zfBmp4 both down-regulated fshr, while up-regulated lhcgr expression at 24 h of co-culturing. This finding, together with the high expression level of BMP receptors in the follicle cells prior to oocyte maturation, strongly suggests a potential role for BMPs in the differential expression of fshr and lhcgr, especially in the full-grown follicles before maturation. As BMPs are largely expressed in the oocyte, this also implies an important role for the oocyte in orchestrating the differentiation and function of the follicle cells.

Bone morphogenetic protein 6 promotes FSH receptor and anti-Müllerian hormone mRNA expression in granulosa cells from hen prehierarchal follicles

A growing body of literature provides evidence of a prominent role for bone morphogenetic proteins (BMPs) in regulating various stages of ovarian follicle development. Several actions for BMP6 have been previously reported in the hen ovary, yet only within postselection (preovulatory) follicles. The initial hypothesis tested herein is that BMP6 increases FSH receptor (FSHR) mRNA expression within the granulosa layer of prehierarchal (6-8 mm) follicles (6-8 GC). BMP6 mRNA is expressed at higher levels within undifferentiated (1-8 mm) follicles compared with selected (≥9 mm) follicles. Recombinant human (rh) BMP6 initiates SMAD1, 5, 8 signaling in cultured 6-8 GC and promotes FSHR mRNA expression in a dose-related fashion. In addition, a 21 h preculture with rhBMP6 followed by a 3 h challenge with FSH increases cAMP accumulation, STAR (StAR) expression, and progesterone production. Interestingly, rhBMP6 also increases expression of anti-Müllerian hormone (AMH) mRNA in cultured 6-8 GC. This related BMP family member has previously been implicated in negatively regulating FSH responsiveness during follicle development. Considering these data, we propose that among the paracrine and/or autocrine actions of BMP6 within prehierarchal follicles is the maintenance of both FSHR and AMH mRNA expression. We predict that before follicle selection, one action of AMH within granulosa cells from 6 to 8 mm follicles is to help suppress FSHR signaling and prevent premature granulosa cell differentiation. At the time of selection, we speculate that the yet undefined signal directly responsible for selection initiates FSH responsiveness. As a result, FSH signaling suppresses AMH expression and initiates the differentiation of granulosa within the selected follicle.

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.

Early avian follicular development is characterized by changes in transcripts involved in steroidogenesis, paracrine signaling and transcription

The mechanisms associated with follicular activation and early growth are not well understood in avian species. Level of mRNA transcripts involved in steroidogenesis (STAR, HSD3B, CYP11A1, CYP19), paracrine signaling (AMH, BMP2, BMP4, BMP6, KITL, WNT4, and PCSK6) and transcription (SMAD1, SMAD2, SMAD3, SMAD5, SMAD9, FOXL3, FOXL2, NR5A1 (SF1), and WT1) were determined in small avian follicles 0.5, 1, and 2 mm in diameter after oocyte removal. STAR, HSD3B, CYP11A1, CYP19, PCSK6, FOXO3, and KITL mRNA increased 2- to 45-fold, while FOXL2, WT1, and WNT4 decreased 30-90% and NR5A1 did not change as follicles developed from 0.5 to 2 mm. Phosphorylated SMAD2, SMAD3, SMAD1/5/9 and FOXO3 proteins were found in both granulosa cells and oocytes of small (<0.5 mm) and larger (>1 mm) follicles. In contrast, non-phosphorylated FOXO3 protein was found in oocyte and granulosa cells of small follicles, but only in the oocyte of larger follicles. Culture of small avian follicles on the chorioallantoic membrane of chick embryos (in ovo) for 7 days caused changes in transcript levels that were similar to changes observed in vivo. The collective findings suggest that the growth of avian follicles from 0.5 to 2 mm is marked by an increase in steroidogenic capacity, and changes in paracrine signaling that may be important during early avian follicular development. Thus, a number of candidate marker genes were identified, and a method of follicle culture was developed to study early follicular development in a model avian species.

Bone morphogenetic protein 2 inhibits FSH responsiveness in hen granulosa cells

Prior to follicle selection into the preovulatory hierarchy, hen granulosa cells from prehierarchal follicles remain undifferentiated, as defined in part by the virtual absence of LHR mRNA expression and inability to produce progesterone. It has previously been proposed that prior to follicle selection, granulosa cells are actively maintained in an undifferentiated state by epidermal growth factor receptor ligands (EGFRL) signaling via the MAP kinase/extracellular regulated kinase pathway. Moreover, there is recent evidence that EGFRL/MAP kinase signaling modulates FSH receptor (FSHR) transcription, in part, via inhibitor of differentiation/DNA-binding (ID) proteins. In the present studies with undifferentiated granulosa, recombinant human (rh) bone morphogenetic protein 2 (BMP2) induced the phosphorylation of SMAD1/5/8, and blocked transforming growth factor β and FSH-induced FSHR expression and progesterone production. Significantly, BMP2 rapidly induced mRNAs encoding betacellulin and EGF, plus ID proteins (ID1, ID3, and ID4). Alternatively, the bioactivity of BMPs can be modulated by one or more BMP antagonists, including noggin (NOG). NOG mRNA is expressed by both hen granulosa and theca tissues from prehierarchal follicles. Pretreatment of cultured granulosa with rh NOG reversed both the stimulatory effects of BMP2 on ID1, ID3, and ID4 expression and the inhibitory effects of BMP2 on FSHR mRNA levels and progesterone production. Collectively, these data provide evidence that prior to follicle selection, BMP2 signaling contributes toward maintaining granulosa cells in an undifferentiated state. The actions of BMP2 are, at least in part, mediated indirectly via enhanced EGFRL expression and ERBB receptor-mediated MAP kinase signaling, and can be modulated by the autocrine/paracrine production of NOG.

Temporal mRNA expression of transforming growth factor-beta superfamily members and inhibitors in the developing rainbow trout ovary

During mammalian ovarian development transforming growth factor-beta (TGFbeta) superfamily members and their inhibitors are critical paracrine regulators, yet the intraovarian functions of these proteins have received less attention in fish. Using quantitative real-time RT-PCR, changes in ovarian mRNA expression of six TGFbeta members and two inhibitors were investigated in rainbow trout across a wide range of fish ovarian stages (i.e., early perinucleous stage through acquisition of maturational competence). Transcript changes for insulin-like growth factor 1 and 2, and five enzymes associated with steroidogenesis, as well as plasma levels of three sex steroids were also measured to provide a framework of established intraovarian regulators in trout. Expression of bone morphogenetic protein 4 (bmp4), bone morphogenetic protein7 (bmp7), and growth differentiation factor 9 (gdf9) peaked during pre-vitellogenic stages and steadily decreased through advancing stages implicating these genes in early ovarian development. A dramatic increase in inhibin beta(A) and decrease in follistatin expression occurred during early to mid-vitellogenic stages, which corresponded with increased 17beta-estradiol plasma levels suggesting a vitellogenic role for ovarian activin A. Follicles that were competent to respond to the maturation-inducing hormone had decreased levels of inhibin beta(B) and increased expression of bambi (bmp and activin membrane-bound inhibitor) suggesting their roles in maturation processes. Furthermore, bmp4, bmp7 and gdf9 are primarily expressed in the oocyte whereas the inhibin subunits, follistatin, and bambi are primarily expressed in the somatic follicle cells. These results support TGFbeta superfamily members and their inhibitors have wide-ranging and disparate roles in regulating ovarian development in fish.

Intra-ovarian growth factors regulating ovarian function in avian species: a review

There is now overwhelming evidence that the avian ovary is a site of production and action of several growth factors that have also been implicated in the functioning of the mammalian ovary. Several members of the Insulin-like growth factor family (IGF), the Epidermal growth factor family (EGF), the Transforming growth factor-beta family (TGF-beta), Fibroblast growth factors (FGF), the Tumour necrosis factor-alpha (TNF-alpha), and others, have been identified either in the granulosa and/or theca compartments of ovarian follicles and in the embryonic and juvenile ovary. Some have been specifically localized to the germinal disc area containing the oocyte. The mRNAs and proteins of the growth factors, receptor proteins and binding proteins of some of the members of each group have been reported in the chicken, turkey, quail and duck. The intra-ovarian roles reported for the different growth factors include regulation of cell proliferation, steroidogenesis, follicle selection, modulation of gonadotrophin action, control of ovulation rate, cell differentiation, production of growth factors, etc. The aim of this paper is to provide a review of the current knowledge of avian ovarian growth factors and their biological activity in the ovary. The review covers the detection of the growth factor proteins, the receptor proteins, binding proteins, their spatial and temporal distribution in embryonic, juvenile and adult ovaries and their regulation. The paper also discusses their roles in each follicular compartment during follicular development. Greater emphasis is given to the major growth factors that have been studied to greater detail and others are discussed very briefly.