cDNA microarray reveals signaling pathways involved in hormones expression of human pituitary

Transcriptomic analysis of the porcine anterior pituitary gland during the peri-implantation period

The peri-implantation period is controlled by signals originating from hypothalamic-pituitary-ovarian axis, uterus and developing embryos. The transcriptomic activity of the anterior pituitary gland may be important for the control of the peri-implantation period. The aim of this study was to determine the alternations in the transcriptomic profile of porcine anterior pituitary gland during the peri-implantation period (days 15-16 of pregnancy) in comparison with established for the respective days of the oestrous cycle. Analysis using a microarray approach indicated that the 651 genes (fold-change ˂1.2; p ≤ .05) were differentially expressed (DEGs) in the anterior pituitary of pigs during the peri-implantation period when compared to cyclic females. Of these DEGs, 404 were upregulated and 247 downregulated. Analysis of occurred relationships among DEGs revealed that some of them are involved in steroid-response and oestrogen synthesis, FSH secretion, immune response, PPAR signalling pathway and the potential for DNA methylation. In conclusion, the altered transcriptomic profile of the porcine pituitary gland in pigs during the peri-implantation period indicates the role of embryos presence in the creation of transcriptomic activity of the pituitary gland in pigs.

Dopamine-2 receptor activation suppresses PACAP expression in gonadotrophs

Pituitary adenylate cyclase-activating polypeptide (PACAP) is expressed at a high level in the fetal pituitary and decreases profoundly between embryonic day 19 and postnatal day 1 (PN1), with a further decrease from PN1 to PN4. In this series of experiments, we investigated the hypothesis that dopamine 2 receptor (Drd2) activation interrupts a cAMP-dependent feed-forward loop that maintains PACAP expression at a high level in the fetal pituitary. Using single-cell RT-PCR of pituitary cell cultures from newborn rats, Drd2 mRNA was identified in gonadotrophs that were also positive for PACAP mRNA. PACAP expression in pituitary cultures from embryonic day 19 rats was suppressed by the PACAP6-38 antagonist and by the Drd2 agonist bromocriptine. Increasing concentrations of bromocriptine inhibited cAMP production as well as cAMP signaling based on cAMP response element-luciferase activity, decreased PACAP promoter activity, and decreased PACAP mRNA levels in αT3-1 gonadotroph cells. Furthermore, blockade of dopamine receptors by injecting haloperidol into newborn rat pups partially reversed the developmental decline in pituitary PACAP mRNA that occurs between PN1 and PN4. These results provide evidence that dopamine receptor signaling regulates PACAP expression under physiological conditions and lend support to the hypothesis that a rise in hypothalamic dopamine at birth abrogates cAMP signaling in fetal gonadotrophs to interrupt a feed-forward mechanism that maintains PACAP expression at a high level in the fetal pituitary. We propose that this perinatal decline in pituitary PACAP reduces pituitary follistatin which permits GnRH receptors and FSH-β to increase to facilitate activation of the neonatal gonad.

Identification of cis elements necessary for glucocorticoid induction of growth hormone gene expression in chicken embryonic pituitary cells

Glucocorticoid (GC) treatment of rat or chicken embryonic pituitary (CEP) cells induces premature production of growth hormone (GH). GC induction of the GH gene requires ongoing protein synthesis, and the GH genes lack a canonical GC response element (GRE). To characterize cis-acting elements and identify trans-acting proteins involved in this process, we characterized the regulation of a luciferase reporter containing a fragment of the chicken GH gene (−1727/+48) in embryonic day 11 CEP cells. Corticosterone (Cort) increased luciferase activity and mRNA expression, and mRNA induction was blocked by protein synthesis inhibition. Through deletion analysis, we identified a GC-responsive region (GCRR) at −1045 to −954. The GCRR includes an ETS-1 binding site and a degenerate GRE (dGRE) half site. Nuclear proteins, including ETS-1, bound to a GCRR probe in electrophoretic mobility shift assays, and Cort regulated protein binding. Using chromatin immunoprecipitation, we found that ETS-1 and GC receptor (GR) were associated with the GCRR in CEP cells, and Cort increased GR recruitment to the GCRR. Mutation of the ETS-1 site or dGRE site in the −1045/+48 GH reporter abolished Cort responsiveness. We conclude that GC regulation of the GH gene during development requires cis-acting elements in the GCRR and involves ETS-1 and GR binding to these elements. Similar ETS-1 elements/dGREs are located in the 5′-flanking regions of GH genes in mammals, including rodents and humans. This is the first study to demonstrate involvement of ETS-1 in GC regulation of the GH gene during embryonic development in any species, enhancing our understanding of GH regulation in vertebrates.

PACAP, an autocrine/paracrine regulator of gonadotrophs

Hypothalamic-hypophysiotropic peptides are the proximate regulators of pituitary cells, but they cannot fully account for the complex functioning of these cells. Accordingly, awareness is growing that an array of peptides produced in the pituitary exert paracrine/autocrine functions. One such peptide, pituitary adenylate cyclase-activating polypeptide (PACAP), was originally identified as a hypothalamic activator of cAMP production in pituitary cells. Gonadotrophs and folliculostellate cells are the main source of pituitary PACAP, and each pituitary cell type expresses a PACAP receptor. PACAP increases alpha-subunit (Cga) and Lhb mRNAs, and it stimulates the transcription of follistatin (Fst) that, in turn, restrains activin signaling to repress Fshb and gonadotropin-releasing hormone-receptor (Gnrhr) expression as well as other activin-responsive genes. The PACAP (Adcyap1) promoter is activated by cAMP, and pituitary cells may communicate by a feed-forward, cAMP-dependent mechanism to maintain a high level of PACAP in the fetal pituitary. At birth, pituitary PACAP declines and pituitary follistatin levels decrease, which together with increased gonadotropin-releasing hormone secretion allow Gnrhr and Fshb to increase and facilitate activation of the newborn gonads. Changes in Adcyap1 expression levels in the adult pituitary may contribute to the selective rise in follicle-stimulating hormone (FSH) from age 20-30 days to the midcycle surge and to the secondary increase in FSH that occurs before estrus. These results provide further support for the notion that PACAP is a key player in reproduction through its actions as a pituitary autocrine/paracrine hormone.

Developmental changes in pituitary adenylate cyclase activating polypeptide expression during the perinatal period: possible role in fetal gonadotroph regulation

Normal reproductive functioning may require secretion of LH independently of FSH. Variation in GnRH pulse frequency and inhibin negative feedback are mechanisms for differential gonadotropin regulation; however, the first instance of differential regulation in rats is during fetal development, prior to the establishment of GnRH connections, when LH accumulates appreciably 2-4 d prior to FSH. Pituitary adenylate cyclase activating polypeptide (PACAP) can differentially regulate the gonadotropins in vitro by stimulating alpha-subunit transcription, lengthening LHbeta transcripts and decreasing FSHbeta mRNA levels, probably through stimulation of follistatin transcription. These experiments are the first to examine whether PACAP influences gonadotroph function in perinatal pituitaries. In vivo, pituitary PACAP mRNA and peptide levels were high at embryonic d 19 and declined by 94 and 85%, respectively, after parturition. This was accompanied by a decrease of 65 and 96% in total follistatin and follistatin-288 mRNAs. These changes were temporally associated with a 20- and 6.5-fold rise in FSHbeta and GnRH receptor mRNAs, respectively, with no significant increase in LHbeta mRNA. In pituitary cell cultures from fetal and postnatal male rats, PACAP mRNA levels were likewise highest in fetal cultures in which the PACAP 6-38 antagonist decreased alpha-subunit and increased FSHbeta mRNA. PACAP 6-38 also reduced basal and GnRH-stimulated LH secretion with little effect on FSH. These data support the hypothesis that PACAP expressed at high levels in the fetal pituitary stimulates alpha-subunit expression and LH secretion and restrains FSH synthesis relative to LH and that a decline in PACAP allows for the neonatal rise in FSH and GnRH receptor because follistatin is decreased.

Identification of candidate genes for human pituitary development by EST analysis

Background

The pituitary is a critical neuroendocrine gland that is comprised of five hormone-secreting cell types, which develops in tandem during the embryonic stage. Some essential genes have been identified in the early stage of adenohypophysial development, such as PITX1, FGF8, BMP4 and SF-1. However, it is likely that a large number of signaling molecules and transcription factors essential for determination and terminal differentiation of specific cell types remain unidentified. High-throughput methods such as microarray analysis may facilitate the measurement of gene transcriptional levels, while Expressed sequence tag (EST) sequencing, an efficient method for gene discovery and expression level analysis, may no-redundantly help to understand gene expression patterns during development.

Results

A total of 9,271 ESTs were generated from both fetal and adult pituitaries, and assigned into 961 gene/EST clusters in fetal and 2,747 in adult pituitary by homology analysis. The transcription maps derived from these data indicated that developmentally relevant genes, such as Sox4, ST13 and ZNF185, were dominant in the cDNA library of fetal pituitary, while hormones and hormone-associated genes, such as GH1, GH2, POMC, LHβ, CHGA and CHGB, were dominant in adult pituitary. Furthermore, by using RT-PCR and in situ hybridization, Sox4 was found to be one of the main transcription factors expressed in fetal pituitary for the first time. It was expressed at least at E12.5, but decreased after E17.5. In addition, 40 novel ESTs were identified specifically in this tissue.

Conclusion

The significant changes in gene expression in both tissues suggest a distinct and dynamic switch between embryonic and adult pituitaries. All these data along with Sox4 should be confirmed to further understand the community of multiple signaling pathways that act as a cooperative network that regulates maturation of the pituitary. It was also suggested that EST sequencing is an efficient means of gene discovery.

Transcriptome analysis of endocrine tumors: clinical perspectives

There is considerable interest in the application of DNA microarrays to the pathologic evaluation of endocrine neoplasms. Improvements in tumor classification and prognostication, prediction of response to therapy, and comprehensive assessment of tumoral hormone production represent the major anticipated benefits. Here, some of the microarray studies that support the clinical use of transcriptome profiling for endocrine tumors are reviewed. In addition, some of the barriers to clinical implementation are discussed.

Gene expression profiling during cellular differentiation in the embryonic pituitary gland using cDNA microarrays

The anterior pituitary is comprised of five major hormone-secreting cell types that differentiate during embryonic development in a temporally distinct manner. Microarrays containing 5,128 unique cDNAs expressed in the chicken neuroendocrine system were produced and used to identify genes with potential involvement in the onset of thyroid-stimulating hormone beta-subunit (TSHbeta), growth hormone (GH), and prolactin (PRL) mRNA during embryonic development. We identified 352 cDNAs that were differentially expressed (P < or = 0.05) on embryonic day 10 (e10), e12, e14, or e17, the period of thyrotroph, somatotroph, and lactotroph differentiation. Self-organizing maps were used to identify genes that may function to initiate hormone gene transcription. Consistent with cellular ontogeny, TSHbeta mRNA increased steadily between e10 and e17, GH mRNA increased between e12 and e17, and PRL mRNA did not increase until e17. Expression of 141 genes increased in a manner similar to TSHbeta mRNA, and 64 genes decreased between e10 and e17. Although genes with these expression profiles are likely involved in development of the pituitary gland as a whole, some of these could be specifically associated with thyrotroph differentiation. Similarly, the expression profiles of 69 and 61 genes indicate a potential involvement in the induction of GH and PRL mRNA, respectively. Quantitative real-time RT-PCR was used to confirm microarray results for 31 genes. This is the first study to evaluate changes in anterior pituitary gene expression during embryonic development of any species using microarrays, and numerous transcription factors and signaling molecules not previously implicated in pituitary development were identified.