Role of Pit-1 in the gene expression of growth hormone, prolactin, and thyrotropin

Comparative genomics reveals functional transcriptional control sequences in the Prop1 gene

Mutations in PROP1 are a common genetic cause of multiple pituitary hormone deficiency (MPHD). We used a comparative genomics approach to predict the transcriptional regulatory domains of Prop1 and tested them in cell culture and mice. A BAC transgene containing Prop1 completely rescues the Prop1 mutant phenotype, demonstrating that the regulatory elements necessary for proper PROP1 transcription are contained within the BAC. We generated DNA sequences from the PROP1 genes in lemur, pig, and five different primate species. Comparison of these with available human and mouse PROP1 sequences identified three putative regulatory sequences that are highly conserved. These are located in the PROP1 promoter proximal region, within the first intron of PROP1, and downstream of PROP1. Each of the conserved elements elicited orientation-specific enhancer activity in the context of the Drosophila alcohol dehydrogenase minimal promoter in both heterologous and pituitary-derived cells lines. The intronic element is sufficient to confer dorsal expansion of the pituitary expression domain of a transgene, suggesting that this element is important for the normal spatial expression of endogenous Prop1 during pituitary development. This study illustrates the usefulness of a comparative genomics approach in the identification of regulatory elements that may be the site of mutations responsible for some cases of MPHD.

Genetics of growth hormone deficiency

When a child is not following the normal, predicted growth curve, an evaluation for underlying illness and central nervous system abnormalities is required and appropriate consideration should be given to genetic defects causing growth hormone (GH) deficiency. This article focuses on the GH gene, the various gene alterations, and their possible impact on the pituitary gland. Transcription factors regulating pituitary gland development may cause multiple pituitary hormone deficiency but may present initially as GH deficiency. The role of two most important transcription factors, POU1F1 (Pit-1) and PROP 1, is discussed.

Pituitary development and physiology

The functions of the pituitary hormones have been relatively well studied; however, understanding the regulation of their synthesis and release have been an ongoing subject of intense research. This review provides an overview of the pituitary cell types and their hormone products. Current understanding of the expression and regulation of the pituitary hormone genes, control of the synthesis and release of the corresponding hormones, and developmental changes are reviewed. This review concludes with a discussion of several of these genes and the genetic disorders with which they are associated.

Identification and functional analysis of the novel S179R POU1F1 mutation associated with combined pituitary hormone deficiency

CONTEXT

The pituitary-specific transcription factor 1 plays a key role in the development and differentiation of three pituitary cell types: somatotrophs, lactotrophs, and thyrotrophs. Several mutations of the human gene (called POU1F1) have been shown to be responsible for a phenotype of combined pituitary hormone deficiency involving GH, prolactin (PRL), and TSH.

OBJECTIVE

We have identified a novel homozygous C to G mutation in exon 4 of the POU1F1 gene (S179R) in a patient with this rare phenotype. We analyzed the functional consequences of this S179R mutation associated with a single-amino acid change in the POU-specific domain.

METHODS

Consequences of this mutation on transcriptional activities by transfection studies in alphaT3 cells, DNA binding ability by EMSA, structural properties, and nuclear accumulation of POU1F1 were investigated.

RESULTS

The transactivation capacity of this mutant was markedly decreased on the GH1, PRL, TSHbeta, and POU1F1 genes. Interestingly, this mutation abolished the functional interaction of POU1F1 on the PRL promoter with the coactivator cAMP response element-binding protein-binding protein but not with the transcription factor LIM homeodomain transcription factor 3. The S179R mutant displayed normal nuclear accumulation but a markedly decreased binding to a DNA response element in keeping with crystallographic data, suggesting that the S179R mutation might interfere with DNA binding.

CONCLUSIONS

Together with previous data, our study indicates that both DNA binding and interaction with cofactors like cAMP response element-binding protein-binding protein are critical for POU1F1 function and that functional and structural properties of abnormal POU1F1 proteins are variously influenced by the type of mutations.

CLONING OF THE FULL LENGTH PIGPIT1(POU1F1)CDNA AND A NOVEL ALTERNATIVEPIT1TRANSCRIPT, AND FUNCTIONAL STUDIES OF THEIR ENCODED PROTEINS

PIT1 is an essential regulatory gene of growth hormone (GH), prolactin (PRL) and thyrotropin beta subunit (TSHbeta). Previously, a partial pig PIT1 cDNA and a genomic clone of the entire 3' end of the PIT1 gene was isolated, and polymorphisms at PIT1 were associated with several performance traits in the pig. In order to understand the biological function of the pig PIT1 gene and its possible application in swine genetics, reverse transcriptase-polymerase chain reaction (RT-PCR) was used to complete the cloning of the full length cDNA for pig PIT1. The pig PIT1 cDNA and its deduced protein sequence have approximately 90% and 95% identity, respectively, with the PIT1 cDNA and protein of other mammals (human, bovine, sheep and rodents). Surprisingly, sequence comparison to other pig PIT1 sequences indicated only approximately 93% identity. Additional sequencing confirmed our sequence, and identified a new polymorphism in exon 4. Phylogenetic analysis of several mammalian PIT1 sequences indicates sequencing errors may account for the discrepancies observed in the other pig sequences reported. Several PIT1 alternative spliced forms were also identified by RT-PCR. They were the delta3PIT1 (missing entire exon 3), delta4PIT1 (missing entire exon 4) and PIT1beta (additional 26 amino acids inserted in front of exon 2) transcripts. The delta4PIT1 and PIT1beta transcripts have been found to encode functionally different proteins in rodents. The delta3PIT1 transcript is a novel isoform of PIT1. Potentially different functions between pig delta3PIT1 and PIT1 were analyzed by expressing these proteins in bacteria. The E. coli-expressed PIT1 and delta3PIT1 proteins were used with rat growth hormone (rGH) and rat prolactin (rPRL) promoter DNA in DNA mobility shift assays. The results showed that pig PIT1 can specifically bind rGH and rPRL promoter regions, but that the pig delta3PIT1 cannot, even at very high protein concentrations. Possible protein-protein interactions between delta3PIT1 and PIT1 were tested by mixing protein extracts before the gel shift assay, and the results showed that delta3PIT1 protein did not affect PIT1 binding to its target DNA. These data demonstrate the functionality of the PIT1 cDNA cloned in this study, and identify a novel delta3PIT1 transcript which encodes a protein that cannot bind rGH/rPRL target sequences.

The human growth hormone gene contains a silencer embedded within an Alu repeat in the 3'-flanking region

Alu family sequences are middle repetitive short interspersed elements (SINEs) dispersed throughout vertebrate genomes that can modulate gene transcription. The human (h) GH locus contains 44 complete and four partial Alu elements. An Sx Alu repeat lies in close proximity to the hGH-1 and hGH-2 genes in the 3'-flanking region. Deletion of the Sx Alu repeat in reporter constructs containing hGH-1 3'-flanking sequences increased reporter activity in transfected pituitary GC cells, suggesting this region contained a repressor element. Analysis of multiple deletion fragments from the 3'-flanking region of the hGH-1 gene revealed a strong orientation- and position-independent silencing activity mapping between nucleotides 2158 and 2572 encompassing the Sx Alu repeat. Refined mapping revealed that the silencer was a complex element comprising four discrete entities, including a core repressor domain (CRD), an antisilencer domain (ASE) that contains elements mediating the orientation-independent silencer activity, and two domains flanking the CRD/ASE that modulate silencer activity in a CRD-dependent manner. The upstream modulator domain is also required for orientation-independent silencer function. EMSA with DNA fragments representing all of the silencer domains yielded a complex pattern of DNA-protein interactions indicating that numerous GC cell nuclear proteins bind specifically to the CRD, ASE, and modulator domains. The silencer is GH promoter dependent and, in turn, its presence decreases the rate of promoter-associated histone acetylation resulting in a significant decrease of RNA polymerase II recruitment to the promoter. The silencer may provide for complex regulatory control of hGH gene expression in pituitary cells.

Cell proliferation and vascularization in mouse models of pituitary hormone deficiency

Mutations in the transcription factors PIT1 (pituitary transcription factor 1) and PROP1 (prophet of Pit1) lead to pituitary hormone deficiency and hypopituitarism in mice and humans. To determine the basis for this, we performed histological analysis of Pit1- and Prop1-deficient dwarf mouse pituitaries throughout fetal and postnatal development. Pit1-deficient mice first exhibit pituitary hypoplasia after birth, primarily caused by reduced cell proliferation, although there is some apoptosis. To determine whether altered development of the vascular system contributes to hypopituitarism, we examined vascularization from embryonic d 14.5 and throughout development. No obvious differences in vascularization are evident in developing Pit1-deficient pituitaries. In contrast, the Prop1-deficient mouse pituitaries are poorly vascularized and dysmorphic, with a striking elevation in apoptosis. At postnatal d 11, apoptosis-independent caspase-3 activation occurs in thyrotropes and somatotropes of normal but not mutant pituitaries. This suggests that Prop1 and/or Pit1 may be necessary for caspase-3 expression. These studies provide further insight as to the mechanisms of Prop1 and Pit1 action in mice.

Absent or Delayed Adrenarche in Pit-1/POU1F1 Deficiency

Mutations of the PIT1/POU1F1 gene are responsible for a rare variant of anterior hypopituitarism, including deficiency of growth hormone, prolactin and thyrotropin. In 8 ethnically diverse POU1F1-deficient patients (4 different mutations) with normal circulating levels of cortisol and adrenocorticotropic hormone, and with spontaneous onset and progression of puberty, we observed an absence or delay of adrenarche (median circulating dehydroepiandrosterone-sulfate -6.2 SD); in each of the 4 postmenarcheal females, pubarche (i.e. appearance of pubic hair) was also absent or delayed. The absence/delay of adrenarche in POU1F1-deficient patients and the absence/delay of pubarche in POU1F1-deficient females suggest that a POU1F1-dependent factor contributes to the normal development of adrenarche and female pubarche.

MRI of the hypothalamic-pituitary axis in children

In childhood, the MR characteristics of the normal pituitary gland are well established. During the first 2 months of life the adenohypophysis demonstrates high signal. Pituitary gland height (PGH) decreases during the 1st year of life and then increases, reaching a plateau after puberty. The magnetization transfer ratio (MTR) increases in both sexes up to the age of 20 years. On dynamic contrast-enhanced studies, the posterior pituitary lobe enhances simultaneously with the straight sinus, and the adenohypophysis later, but within 30 s. In genetically determined dysfunctional states, the adenohypophysis may be normal, hypoplastic, or enlarged. Pituitary enlargement, observed in Prop 1 gene mutations, is characterized by a mass interposed between the anterior and posterior lobes. An ectopic posterior lobe (EPP), associated with a hypoplastic or absent pituitary stalk, may be observed in patients with hypopituitarism. Tumors of the hypothalamic-pituitary (HP) axis may be the origin of adenohypophyseal deficiencies. A small hypo-intense adenohypophysis is found in iron overload states and is often associated with hypogonadotrophic hypogonadism. Absence of the posterior lobe bright signal, with or without a thick pituitary stalk or a mass at any site from the median eminence to the posterior pituitary lobe, may be found in diabetes insipidus. Hydrocephalus, suprasellar arachnoid cysts, hypothalamic hamartomas and craniopharyngiomas may result in central precocious puberty (CPP). Increased PGH in girls with idiopathic CPP is useful for its differential diagnosis from premature thelarche (PT). Pituitary adenomas, observed mainly in adolescents, present the same MR characteristics as those in adults.

Independent differentiation of mammotropes and somatotropes in the chicken embryonic pituitary gland. Analysis by cell distribution and attempt to detect somatomammotropes

It has been reported that mammotropes in a rodent pituitary gland are derived from somatotropes via somatomammotropes (SMTs), cells that produce both growth hormone (GH) and prolactin (Prl). However, no studies have been done on the transdifferentiation of somatotropes in the chicken pituitary gland. In this study, in order to determine the origin of mammotropes, we studied detail property of appearance of chicken somatotropes, mammotropes and pit-1 cells and then evaluated the existence of SMTs in the chicken embryonic pituitary gland. Immunohistochemical analysis revealed that GH-immunopositive (GH-ip) cells appeared on embryonic day (E) 14 and were mainly distributed in the caudal lobe, while Prl-immunopositive (Prl-ip) cells appeared in the cephalic lobe of the pituitary gland on E16. In situ hybridization (ISH) and RT-PCR analysis showed that expression of GH and Prl mRNA starts at E12 in the caudal lobe and at E14 in the cephalic lobe respectively. Pit-1 mRNA was first detected on E5 by RT-PCR, and pit-1 mRNA-expressing cells were found in the cephalic lobe on E8. Then with the ontogeny of the chicken, these cells spread into both lobes. Using a double staining method with ISH and immunohistochemistry, we could not detect the existence of SMTs in the chicken embryonic pituitary gland even in the marginal region of either lobe. These results suggest that chicken somatotropes and mammotropes independently appear in different lobes of pituitary gland and that transdifferentiation from somatotropes to mammotropes is not the central route for differentiation of mammotropes in the embryonic chicken pituitary gland.

Dietary Soybean Enhances Pit-1 Dependent Pituitary Hormone Production in Iodine Deficient Rats

Reports have shown that soybeans are goitrogenic. In the present study, we investigated the effects of a high soybean diet in rats that were fed normal or iodine-deficient chow on the regulation of anterior pituitary hormone production. Iodine deficiency alone resulted in thyroid hyperplasia, reduced serum thyroxine levels, and a tendency towards an increase in serum thyroid stimulating hormone (TSH). The combination of a high soybean and low iodine diet (ID + DS) acted synergistically to induce thyroid hypertrophy, reduce serum thyroxine and tri-iodothyronine, and markedly increase serum TSH. Immunohistochemical analysis revealed that rats fed the ID + DS diet exhibited a marked increase in their number of pituitary TSH, prolactin (PRL), and growth hormone (GH) producing cells. Pituitary transcription factor-1 (Pit-1) which is involved in the expression of the TSH, PRL, and GH genes was also increased in ID + DS fed rats. These results suggest that a diet high in soybean products modulates anterior pituitary hormone production by regulating Pit-1 induction, in iodine-deficient animals.

Role of PROP1 in pituitary gland growth

Mutations in the PROP1 transcription factor gene lead to reduced production of thyrotropin, GH, prolactin, and gonadotropins as well as to pituitary hypoplasia in adult humans and mice. Some PROP1-deficient patients initially exhibit pituitary hyperplasia that resolves to hypoplasia. To understand this feature and to explore the mechanism whereby PROP1 regulates anterior pituitary gland growth, we carried out longitudinal studies in normal and Prop1-deficient dwarf mice from early embryogenesis through adulthood, examining the volume of Rathke's pouch and its derivatives, the position and number of dividing cells, the rate of apoptosis, and cell migration by pulse labeling. The results suggest that anterior pituitary progenitors normally leave the perilumenal region of Rathke's pouch and migrate to form the anterior lobe as they differentiate. Some of the cells that seed the anterior lobe during organogenesis have proliferative potential, supporting the expansion of the anterior lobe after birth. Prop1-deficient fetal pituitaries are dysmorphic because mutant cells are retained in the perilumenal area and fail to differentiate. After birth, mutant pituitaries exhibit enhanced apoptosis and reduced proliferation, apparently because the mutant anterior lobe is not seeded with progenitors. These studies suggest a mechanism for Prop1 action and an explanation for some of the clinical findings in human patients.

Associations of polymorphisms in the Pit-1 gene with growth and carcass traits in Angus beef cattle12

The Pit-1 gene was studied as a candidate for genetic markers of growth and carcass traits. Angus beef cattle that were divergently selected for high- or low-blood serum IGF-I concentration were used in this study. The single-strand conformation polymorphism method was used to identify polymorphism in the Pit-1 gene including regions from intron 2 to exon 6. Two polymorphisms, Pit1I3H (HinfI) and Pit1I3NL (NlaIII), were detected in intron 3 of the Pit-1 gene. One polymorphism, Pit1I4N (BstNI), was found in intron 4, and a single nucleotide polymorphism, Pit1I5, was found in intron 5. The previously reported polymorphism in exon 6, Pit1E6H (HinfI), was also studied in 416 Angus beef cattle. Associations of the polymorphisms with growth traits, carcass traits, and IGF-I concentration were analyzed using a general linear model procedure. No significant associations were observed between these polymorphisms and growth and carcass traits.

Inactivating Pit-1 mutations alter subnuclear dynamics suggesting a protein misfolding and nuclear stress response

Pit-1, a POU-class nuclear DNA-binding transcription factor, specifies three of the parenchymal cell types in anterior pituitary ontogeny. Using fluorescent fusions and live cell imaging, we have compared the dynamic behavior of wild-type and inactivating Pit-1 point mutations. Fluorescence recovery after photobleaching (FRAP) and real-time extraction data indicate that wild-type Pit-1 has a dynamic mobility profile, with t(1/2s) approximately 5-7 s when expressed from low to high amounts, respectively. Biochemically, Pit-1 is approximately 50% retained according to direct observation during extraction, indicating a dynamic interaction with nuclear structure. An analysis of transiently expressed Pit-1 carrying two different debilitating mutations reveals that they translocate normally to the nucleus, but exhibit two different levels of mobility, both clearly distinguishable from wild-type Pit-1. At low expression levels, the t(1/2s) of Pit(W261C) and Pit(A158P) are extremely rapid (0.3 and 0.6 s t(1/2s), respectively). At higher expression levels, unlike wild-type Pit-1, both mutant proteins become immobilized and insoluble, and fractionate completely with the insoluble nuclear matrix. Relative to wild-type, over expression of mutated Pit-1 elicits a nuclear stress response indicated by increased levels of heat shock inducible heat shock protein 70 (Hsp70), and reorganization of heat shock factor-1. The decreased mobility of Pit(A158P) relative to Pit(W261C) at low expression levels correlates with its ability to partially activate when expressed at low levels and its ability to bind cognate DNA. At high expression levels, lower Pit(A158P) activation correlates with its immobilization and insolubility. These data suggest a link between specific rates of intranuclear mobility and Pit-1 transcription function, perhaps to insure sufficient interactions with chromatin, or in the case of non-DNA binding Pit-1, interaction as a repressor. These data imply inactivating mutations can lead to an intranuclear sorting away from transcription related pathways, and at least in part to a misfolded protein pathway. Taken together, caution is suggested when interpreting point (or other) mutational analyses of transactivator function, as new compartmentation, especially in the context of expression levels, may cloud the distinction between defining functional molecular domains and intranuclear processing of misfolded proteins.

Changes in the population of pituitary protein transcription factor-1 nuclei in the anterior pituitary during withdrawal and resumption of feeding in hens

Pituitary protein transcription factor (Pit-1) is a member of a large family of protein transcription factors that include Pit-1, Oct-1, Oct-2, and Unc-86. The goal of this experiment was to determine whether the population of Pit-1-containing cells changes in the anterior pituitary of chicken by the regulation of feeding. White Leghorn hens were subjected to withdrawal and resumption of feeding. The anterior pituitaries were collected from hens at pretreatment, at 2 d after withdrawal of feeding (2DWF), and 1 d and 5 d after resumption of feeding (1DRF and 5DRF, respectively). Sections of the pituitaries were immunostained for Pit-1. They were examined under a light microscope with an image analysis computer system. The Pit-1 positive nuclei were found in the glandular cells in the cephalic and caudal lobes of the anterior pituitary in all four groups of hens. The Pit-1 cell population significantly increased in the 2DWF and 1DRF and decreased thereafter in 5DRF. These results suggests that feed withdrawal may stimulate Pit-1 expression in chicken, suggesting that Pit-1 may be involved in control of pituitary functions during the process of feed regulation.

New N-terminal located mutation (Q4ter) within the POU1F1-gene (PIT-1) causes recessive combined pituitary hormone deficiency and variable phenotype

OBJECTIVE

Growth is an inherent property of life. About 10% of the congenital forms of growth retardation and short stature are genetically caused. Beside the gene involved in direct GH-production, there are different candidate genes important for appropriate pituitary development causing combined pituitary hormone deficiency (CPHD). However, severe growth retardation and failure to thrive remain the leading reason for medical assessment in these patients.

PATIENTS AND METHODS

We report two siblings of a healthy but consanguineous Malaysian family presenting with severe short stature caused by CPHD with a variable phenotype. Importantly, at the beginning the girl presented with isolated GHD, whereas the boy was hypothyroid. As the most common gene alterations responsible for CPHD are within either the PROP-1- or the POU1F1- (PIT-1)-gene these two genes were further studied.

RESULTS

Subsequent sequencing of the six exons of the POU1F1-gene allowed the identification of a new N-terminal mutation (Q4ter) in these two children. A substitution of C to T induced a change from a glutamine (CAA) to a stop codon (TAA) in exon 1 of the PIT-1 protein. Both affected children were homozygous for the mutation, whereas the mother and father were heterozygous.

CONCLUSION

We describe two children with autosomal recessive inherited CPHD caused by a new N-terminal located mutation within the PUO1F1-gene. The clinical history of these two children underline the phenotypic variability and support the fact that children with any isolated and/or combined PHD need to be closely followed as at an any time other hormonal deficiencies may occur. In addition, molecular analysis of the possible genes involved might be most helpful for the future follow-up.

Expression of growth hormone and its transcription factor, Pit-1, in early bovine development

During bovine embryogenesis, bovine growth hormone (bGH) contributes to proliferation, differentiation, and modulation of embryo metabolism. Pituitary-specific transcription factor-1 (Pit-1) is a transcription factor that binds to promoters of GH, prolactin (PRL), and thyroid-stimulating hormone-beta (TSHbeta) encoding genes. A polymorphism in the fifth exon of the bGH gene resulting in a leucine (Leu) to valine (Val) substitution provides an Alu I restriction site when the Leu allele is present. To determine the onset of embryonic expression of the bGH gene, oocytes derived from ovaries homozygous for Leu alleles were fertilized in vitro with spermatozoa obtained from a Val homozygote. For each developmental stage examined, three separate pools of embryos composed of approximately 100 cell samples underwent RNA isolation, reverse transcription to cDNA, and amplification by nested PCR (nPCR). Bovine GH gene transcripts were identified at 2- to 4-cell (n = 162), 8- to 16-cell (n = 73), morulae (n = 51), and blastocyst (n = 15) stages. Likewise, transcripts for Pit-1 were detected at 2-cell (n = 125), 4-cell (n = 114), 8-cell (n = 56), 12-to-32-cell (n = 32), morulae (n = 68), and blastocyst (n = 14) stages. After digestion with Alu1, bGH cDNA was genotyped by restriction fragment length polymorphism (RFLP) analysis. Bovine GH mRNA was present in all pools of stages examined. Both Leu and Val alleles (maternal and paternal) were only detected in pools of embryos that had reached 8- to 16-cell stage. Results suggest that transcription of the bGH gene begins at the 8- to 16-cell stage in bovine embryos, possibly under control of the transcription factor, Pit-1, and that RFLP analysis of the bGH gene can be used to determine parental origin of transcripts in early embryonic development.

Genetic characterization of growth hormone deficiency and resistance: implications for treatment with recombinant growth hormone

Growth failure can be caused by deficient growth hormone production or action. The genes involved in pituitary development, somatotrope function, as well as growth hormone synthesis, secretion, and action have recently been characterized in considerable detail. Familial growth failure has played an important role in identifying these genes, and a large number of mutations adversely affecting the development and function of the growth hormone/insulin-like growth factor axis have been discovered. Inactivating mutations leading to growth retardation in humans have been identified in several pituitary transcription factor genes (HESX1, PITX2, LHX3, PROP1, POU1F1) as well as in genes encoding the growth hormone-releasing hormone receptor (GHRH-R), the G(s) protein alpha subunit (GNAS1), growth hormone itself (GH-1), the growth hormone receptor (GHR), and in a single case each, the insulin-like growth factor I (IGF-I) and the IGF-I receptor. Mutations in pituitary transcription factors cause developmental abnormalities of the pituitary and deficiency of multiple pituitary hormones [growth hormone (GH), prolactin (Prl), thyrotropin (TSH) and lutropin/follitropin (LH/FSH)]. Most of the syndromes respond well to therapy with recombinant GH; exceptions are antibody-mediated resistance in GHD type IA (not all patients) and cases of Laron syndrome (GHR deficiency). Such patients respond to IGF-I therapy. This review summarizes the molecular genetics, functional defects, phenotypes, diagnostic considerations and therapeutic aspects of syndromes associated with mutations in the relevant genes.

A functional promoter polymorphism in the macrophage migration inhibitory factor (MIF) gene associated with disease severity in rheumatoid arthritis

The macrophage migration inhibitory factor (MIF) is a potent pro-inflammatory cytokine and regulates the anti-inflammator effects of glucocorticoids. An important role for MIF within the cytokine cascade is to act in concert with endogenous glucocorticoids to control the set-point and magnitude of the inflammatory response. Elevated expression of MIF in the circulation and in the synovial joint has been documented in rheumatoid arthritis. MIF also has been linked to the development of joint damage and disease pathology in experimental animal models. We describe herein a novel CATT-tetranucleotide repeat polymorphism at position -794 of the human Mif gene and show that it functionally affects the activity of the MIF promoter in gene reporter assays. We describe four genotypes which comprise 5, 6, 7, or 8-CATT repeat units and show that the 5-CATT allele has the lowest level of basal and stimulated MIF promoter activity in vitro. The presence of the low expressing, 5-CATT repeat allele correlated with low disease severity in a cohort of rheumatoid arthritis patients.

The turkey transcription factor Pit-1/GHF-1 can activate the turkey prolactin and growth hormone gene promoters in vitro but is not detectable in lactotrophs in vivo

The transcription factor Pit-1/GHF-1 plays an important role in regulating the prolactin (Prl) and growth hormone (GH) genes in mammals. In this study, the role that Pit-1 plays in regulating the prolactin and growth hormone genes in avian species was examined by cotransfection assays and immunofluorescence staining of pituitary sections. In cotransfection assays, turkey Pit-1 activated the turkey Prl, turkey GH, and rat Prl promoters 3.8-, 3.7-, and 12.5-fold, respectively. This activation was comparable to rat Pit-1 activation of these same promoters. A point mutation in the turkey Pit-1 cDNA, which changed leu-219 to ser-219, resulted in a 2-, 2-, and 10-fold reduction in the activation of the turkey Prl, turkey GH, and rat Prl promoters, respectively. Unexpectedly, coexpression of tPit-1 (leu-219) and tPit-1(ser-219) activated turkey Prl and rat Prl promoters 9.4- and 35.9-fold, respectively, but had no effect on the turkey GH promoter. Dual-label immunofluorescence analysis of turkey pituitary sections revealed that Pit-1 was not detectable in prolactin-staining cells but was detectable in GH-staining cells. Taken together, these data indicate that in the domestic turkey, Pit-1 can activate the turkey Prl promoter in vitro, but does not appear to play a role in regulating Prl gene expression in vivo. Pit-1, however, still likely plays a role in regulating GH gene expression.

Hereditary gingival fibromatosis and growth retardation

OBJECTIVE

To describe two patients with hereditary gingival fibromatosis (HGF) and growth hormone deficiency and to review the literature on HGF and related endocrine abnormalities.

METHODS

We present case reports of two patients (first cousins)-an 8-year-old girl and a 13-year-old boy-with an existing diagnosis of HGF, who were assessed because of presumed growth failure. Both patients underwent growth hormone stimulation testing and more in-depth endocrine evaluation, including measurement of morning cortisol, adrenocorticotropic hormone (ACTH), and prolactin levels as well as thyroid function tests. An ACTH stimulation test was also performed. Radiologic evaluation included assessment of bone age and magnetic resonance imaging of the brain.

RESULTS

In addition to HGF, both patients had short stature, subnormal growth velocity, and delayed bone age but no abnormalities on magnetic resonance imaging of the brain. Serum prolactin levels and results of thyroid function tests were normal. Subnormal growth hormone response was noted during hypoglycemia and pharmacologic stimuli with clonidine and levodopa. The female patient, who also had recurrent hypoglycemic episodes, had a suboptimal cortisol and ACTH response during hypoglycemia. On the ACTH stimulation test, she showed an inadequate cortisol response at 30 minutes but a normal response at 60 minutes. The male patient had normal morning cortisol and ACTH levels plus a normal response to ACTH stimulation. Both patients are responding well to treatment with growth hormone. The girl is also receiving cortisol replacement and has had no further episodes of hypoglycemia.

CONCLUSION

Although HGF has been described as an isolated finding, it can occur as part of a syndrome, including infrequent endocrine abnormalities such as growth hormone insufficiency. The cause of the growth hormone deficiency remains unclear in these two patients. We believe that patients with HGF should be monitored carefully for a prolonged period for growth as well as other endocrine abnormalities.

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

Pituitary hormone gene expression and secretion in human growth hormone-releasing hormone transgenic mice: focus on lactotroph function

The human GH-releasing hormone (hGHRH) transgenic mouse has a hyperplastic anterior pituitary gland that eventually develops into an adenoma. We showed previously that the number of lactotrophs in the male hGHRH transgenic mouse is increased 2-fold, yet there is no concomitant increase in plasma levels of PRL. To further elucidate underlying changes in lactotroph function in the hGHRH transgenic mouse, the objectives of this study were to 1) examine the relative differences in PRL gene expression in transgenic mice and their siblings, 2) quantify PRL secretion at the level of the individual cell, 3) determine whether tyrosine hydroxylase gene expression and/or activity are altered in the hypothalamus of transgenic mice, and 4) assess dopamine receptor gene expression and functional sensitivity in lactotrophs of transgenic mice. Total PRL messenger RNA (mRNA) levels were increased nearly 5-fold in the hGHRH transgenic mouse, whereas the concentrations of PRL mRNA (PRL mRNA per microg total RNA) were unchanged. In contrast, total PRL contents were unchanged, whereas the concentrations of PRL (micrograms of PRL per mg total protein) were decreased 3-fold. Hypothalamic tyrosine hydroxylase steady state mRNA levels were not altered in the hGHRH transgenic mice, but hypothalamic tyrosine hydroxylase activity was increased 2-fold in transgenic mice. Dopamine D2 receptor mRNA concentrations in the anterior pituitary were increased 2.5-fold in hGHRH transgenic mice, and total pituitary D2 receptor mRNA levels were increased nearly 10-fold. Furthermore, the basal secretory capacity of lactotrophs from transgenic mice was increased significantly at the level of the single cell, and dopamine inhibited the secretion of PRL to a greater extent in hGHRH transgenic mice. Thus, although the total number of lactotrophs is increased 2-fold in hGHRH transgenic mice, the present data are consistent with the hypothesis that increased hypothalamic dopamine synthesis and release coupled with an increase in D2 dopamine receptor gene expression and functional sensitivity in the pituitary result in normal plasma levels of PRL.

Transcription factors regulating pituitary development

This review will address contributions of nuclear transcription factors to the embryologic development and definitive function of the anterior pituitary gland. The HESX1, PITX1, PITX2, PROP1 and POU1F1 genes are of particular interest because of their recognized or potential associations with human disease. Mutations of any of the first three genes produce complex disease phenotypes such as septo-optic dysplasia, Treacher Collins Franceschetti syndrome or Rieger syndrome that may include deficiency of one or more pituitary hormones. Mutations in PROP1 or POU1F1, or their mouse homologous, result in severe hypopituitarism as well as morphological abnormalities of the pituitary gland.

Phenotype and genetic analysis of a syndrome caused by an inactivating mutation in the growth hormone-releasing hormone receptor: Dwarfism of Sindh

We report, in detail, a new form of familial dwarfism, including its phenotypic features, hormonal profile, and molecular basis. Following a newspaper report of severe dwarfism in two villages in the province of Sindh, Pakistan, we organized an expedition to study its clinical, genetic, and molecular characteristics. We identified 18 dwarfs (15 male, 3 female), all members of a consanguineous kindred, ranging in age from newborn to 28 yr. Mean height was 7.2 SD below the norm, with mean adult heights of 130 cm for males and 113.5 cm for females. Body proportions and habitus were normal; but head circumference was 4.1 SD, and blood pressure approximately 3 SD below the norm. There was no dysmorphism, no microphallus, and no history of hypoglycemia. Serum GH did not respond to provocative stimuli (GHRH, L-dopa, or clonidine). Insulin-like growth factor I (IGF-I) and IGF-binding protein 3 were low (5.2 +/- 2.0 ng/mL and 0.42 +/- 0.13 microg/mL, respectively; mean +/- SD) but rose normally with GH treatment. One affected, dwarfed couple had a son, demonstrating fertility in both sexes. Clinical and endocrinological evidence suggested isolated GH deficiency with a recessive inheritance pattern. The GH-N gene was found to be intact. Linkage analysis of microsatellite chromosomal markers near other candidate genes yielded a high LOD score (6.26) for the GHRH receptor (GHRH-R) locus. DNA sequencing revealed a nonsense mutation (Glu50-->Stop) in the extracellular domain of the GHRH-R. This mutation predicts a severely truncated GHRH-R; it is identical to that recently reported in four patients from two other families. Inheritance is autosomal recessive (chromosome 7p) with a high degree of penetrance. Relatives heterozygous for the mutation had moderately decreased IGF-I levels and slightly blunted GH responses to GHRH and L-dopa, but they showed only minimal or no height deficit. This syndrome represents the human homologue of the little (lit/lit) mouse and closely resembles its phenotype. It demonstrates the absolute requirement of GHRH signaling for pituitary GH secretion and postnatal growth in humans, and its relatively minor (but discernible) biological importance in extrapituitary sites. The syndrome is distinct from other forms of GH deficiency with respect to microcephaly, asymptomatic hypotension, and absence of features such as facial dysplasia, significant truncal obesity, microphallus, or hypoglycemia. Its discovery raises the possibility of milder mutations in the GHRH-R gene as potential causes for partial GH insufficiency and idiopathic short stature.

Evidence for the presence of the tissue-specific transcription factor Pit-1 in lancelet larvae

Recent molecular studies have noted the affinity among cephalochordates and vertebrates. In particular, a cluster of vertebrate-like homeobox genes regulates the development of the lancelet Branchiostoma lanceolatum. A previous study has outlined the expression pattern of the pituitary-specific transcription factor Pit-1 in adult lancelets. Pit-1 belongs to the POU family of transcription factors, which, like homeotic proteins, are members of the helix-turn-helix superfamily of proteins. POU is an acronym for Pit-1, Oct-1 and Oct-2, and Unc-86. In the present work, we investigated the head region of premetamorphic larvae of B. lanceolatum, by means of scanning electron microscopy, wholemount and tissue sections immunocytochemistry, and Western blotting assay, to verify the presence and distribution of Pit-1. Immunoreactive Pit-1 protein was detected in the rostral nerves and in a cluster of photoreceptor cells of the frontal eye. At the same time, an electrophoretic band of 33 kDa was shown from extracts of premetamorphic larvae and recognized by a monoclonal antibody to rat Pit-1. On the basis of the immunocytochemical and electrophoretic results, we can assume that Pit-1 may play a neuromodulatory role in the larval central nervous system. Moreover, the spatial and temporal distribution of Pit-1 protein in larva and adult lancelets agrees only in part with that described in embryonic and adult mice, suggesting different molecular controls of regional identity in the nervous system of cephalochordates and vertebrates.

Description of a Brazilian patient bearing the R271W Pit-1 gene mutation

The pituitary-specific transcription factor Pit-1/GHF-1 is responsible for pituitary development and expression of somatotrophs and lactotrophs as well as hormonal regulation of the prolactin (PRL) and thyrotropin (TSH) beta genes by thyrotropin-releasing hormone (TRH) and cyclic adenosine monophosphate (cAMP). Pit-1 gene mutations result in complete growth hormone (GH) and PRL deficiencies and variable degrees of TSH deficiency, producing the clinical syndrome of combined pituitary hormone deficiency (CPHD). Several cases of mutations in the Pit-1 gene have been reported; the most common one is a sporadic mutation altering an arginine (R) to a tryptophan (W) in codon 271, in one allele of the Pit-1 gene. We describe a case of a 38-year-old woman, born to consanguineous parents, presenting with growth failure and hypothyroidism. Growth failure was noted from early infancy, whereas hypothyroidism was only apparent from adolescence. She had almost undetectable GH and PRL levels and an inappropriate low TSH for very low triiodothyronine (T3) and thyroxine (T4) levels, while the remaining pituitary evaluation was normal. The pituitary gland was hypoplastic by magnetic resonance imaging. A point mutation in exon 6, monoallelic, causing a C to T substitution that changes amino acid 271 from Arg (R) to Trp (W) was identified. Children with Pit 1 mutations and delayed onset of hypothyroidism may be initially diagnosed as isolated GH deficiency.