A tissue-specific transcription factor containing a homeodomain specifies a pituitary phenotype

A novel nonsense mutation in the Pit-1 gene: evidence for a gene dosage effect

The POU transcription factor Pit-1 functions in the development of somatotrophs, lactotrophs, and thyrotrophs of the anterior pituitary gland. It also plays a role in cell-specific gene expression and regulation of the gene products from these cell types, GH, prolactin, and TSH, respectively. In the present report we studied a patient with severe growth failure. Provocative studies revealed undetectable GH, prolactin, and TSH levels, and her pituitary gland was hypoplastic on magnetic resonance imaging. She had a novel homozygous nonsense mutation in the 3' end of the first alpha-helix of the POU-specific domain of the Pit-1 gene. This mutation results in a truncated protein with loss of most of the Pit-1 DNA-binding domains. Interestingly, her parents, who each have one mutant allele, have evidence of mild endocrine dysfunction. Thus, two normal copies of the Pit-1 gene appear necessary for full Pit-1 gene function.

Identification of a new growth hormone family protein, somatolactin-like protein, in the rainbow trout (Oncorhyncus mykiss) pituitary gland

A cDNA encoding a new GH family protein expressed in the rainbow trout (Oncorhyncus mykiss) pituitary gland was identified. Because the deduced amino acid sequence of this cDNA shares 56% homology with rainbow trout (rt) somatolactin (rtSL), we named it as rtSL-like protein (rtSLP). Comparison of the amino acid sequences of rtGH, rainbow trout prolactin (rtPRL), and rtSLP revealed that rtSLP shares 26% and 21% identity with that of rtGH and rtPRL, respectively. Trout SLP contains not only the known GH family protein conserved domains but also all of the four cysteine residues that are responsible for the formation of two disulfide linkages in GH, PRL, and SL. Immunoblot analysis revealed that rtSLP is secreted from the pituitary gland once it is synthesized. Unlike rtSL, rtSLP mRNA was readily detectable in pituitary glands of 2-yr fish (30-34 cm in length) but not in embryos or 1-yr fish (17-25 cm in length). Furthermore, the level of rtSLP mRNA in male fish is 2-fold higher than that in female fish. These results suggest that rtSLP might play a role in regulating the reproductive maturation in rainbow trout.

Structure, mRNA expression and linkage mapping of the brain-type fatty acid-binding protein gene (FABP7) from zebrafish (Danio rerio)

The brain fatty acid-binding protein (B-FABP) is involved in brain development and adult neurogenesis. We have determined the sequence of the gene encoding the B-FABP in zebrafish. The zebrafish B-FABP gene spans 2370 bp and contains four exons interrupted by three introns. The coding sequence of zebrafish B-FABP gene is identical to its cDNA sequence and the coding capacity of each exon is the same as that for the human and mouse B-FABP genes. A 1249 bp sequence 5' upstream of exon 1 of the zebrafish B-FABP gene was cloned and sequenced. Several brain development/growth-associated transcription factor binding elements, including POU-domain binding elements and the proposed lipogenic-associated transcription factor NF-Y elements, were found within the 5' region of the B-FABP gene. RT-PCR analysis using mRNA extracted from different tissues of adult zebrafish demonstrated that the zebrafish B-FABP mRNA was predominant in brain with lower levels in liver, testis and intestine, but not in ovary, skin, heart, kidney and muscle. Quantitative RT-PCR revealed a similar tissue-specific distribution for zebrafish B-FABP mRNA except that very low levels of B-FABP mRNA, normalized to beta-actin mRNA, were detected in the heart and muscle RNA, but not in liver RNA. Zebrafish B-FABP mRNA was detected by RT-PCR in embryos beyond 12 h postfertilization, suggesting a correlation of zebrafish B-FABP mRNA expression with early brain development. Radiation hybrid mapping assigned the zebrafish B-FABP gene to linkage group 17. Conserved syntenies of the zebrafish B-FABP gene and the human and mouse orthologous B-FABP genes were observed by comparative genomic analysis.

Endocrine pathology in translational medicine: an overview of current and future prospects

With applications of recent development of molecular techniques, endocrine pathology, as a scientific discipline, has been expanding its field to cover not only the pathologic diagnosis but also molecular mechanisms of hormone production and secretion as well as implementation for appropriate therapeutic approaches. In this review, the discussion includes molecular markers for the diagnosis of neuroendocrine (NE) tumors focusing on various proteins for the transport of secretory granules. MIB-1, proliferative indices, is particularly useful to access biologic activities of NE tumors. The specific hormone production relies on the expression of combination of transcription factors and proteolytic digestion (processing) of prohormones by specific enzymes, prohormone convertases PC1/3 and PC2. Inappropriate processing of prohormones sometimes are related to neoplastic conditions. Endocrine therapeutics have been focusing on the compensation of deficient hormones by transplanting specific hormone producing cells including embryonic stem (ES) cells. The endocrine pathology is expected to play a major role in translational medicine.

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.

Novel function of the transactivation domain of a pituitary-specific transcription factor, Pit-1

Pit-1 stimulates the expression of growth hormone, prolactin, and thyrotropin beta subunit genes. Consequently, abnormality of the Pit-1 gene results in combined pituitary hormone deficiency (CPHD). In this study, we analyzed the function of Pit-1 with a mutation (proline to leucine at codon 24) in the transactivation domain, P24L, which has a normal POU domain important for binding to DNA, because this mutation had been reported in a patient with CPHD. We found that codon 24 proline in the transactivation domain as well as the POU domain of Pit-1 was crucial to recruit coactivator CREB-binding protein (CBP) in the cultured cells. P24L completely lost the responsiveness to cAMP to stimulate the expression of the Pit-1-targeted genes. Furthermore, CBP and Pit-1, but not P24L, markedly enhanced the expression of the Pit-1-targeted gene to cAMP, and adenovirus E1a that binds to CBP and abrogates its function blocked the induction by cAMP of Pit-1-stimulated gene transcription in the pituitary-derived GH3 cells. These results suggest that CBP and proline at codon 24 in the transactivation domain of Pit-1 are important for the cAMP-induced activation of Pit-1-targeted genes. However, P24L maintained basal transcriptional activity, suggesting that CBP is unlikely to be an essential coactivator for Pit-1.

Domains of Pit-1 required for transcriptional synergy with GATA-2 on the TSH beta gene

Previous studies showed that Pit-1 functionally cooperates with GATA-2 to stimulate transcription of the TSH beta gene. Pit-1 and GATA-2 are uniquely coexpressed in pituitary thyrotropes and activate transcription by binding to a composite promoter element. To define the domains of Pit-1 important for functional cooperativity with GATA-2, we cotransfected a set of Pit-1 deletions with an mTSH beta-luciferase reporter. Plasmids were titrated to express equivalent amounts of protein. A mutant containing a deletion of the hinge region between the POU and homeodomains retained the ability to fully synergize with GATA-2. In contrast, mutants containing deletions of amino acids 2-80 or 72-125 demonstrated 56 or 34% of the synergy found with the full-length protein, suggesting that these regions contributed to cooperativity. Mutants with deletions of the POU-specific or homeodomain further reduced the effect signifying the requirement for DNA binding. GST interaction studies demonstrated that only the homeodomain of Pit-1 interacted with GATA-2. Finally, several mutations between the Pit-1 and GATA-2 sites on the TSH beta promoter reduced binding for each factor and greatly reduced ternary complex formation. Thus multiple domains of Pit-1 are required for full synergy with GATA-2 and sequences between the two binding sites contribute to co-occupancy with both factors on the proximal TSH beta promoter.

Specification of unique Pit-1 activity in the hGH locus control region

The human GH (hGH) gene cluster is regulated by a remote 5' locus control region (LCR). HSI, an LCR component located 14.5 kb 5' to the hGH-N promoter, constitutes the primary determinant of high-level hGH-N activation in pituitary somatotropes. HSI encompasses an array of three binding sites for the pituitary-specific POU homeodomain factor Pit-1. In the present report we demonstrate that all three Pit-1 sites in the HSI array contribute to LCR activity in vivo. Furthermore, these three sites as a unit are fully sufficient for position-independent and somatotrope-restricted hGH-N transgene activation. In contrast, the hGH-N transgene is not activated by Pit-1 sites native to either the hGH-N or rat (r)GH gene promoters. These findings suggest that the structures of the Pit-1 binding sites at HSI specify distinct chromatin-dependent activities essential for LCR-mediated activation of hGH in the developing pituitary.

Molecular basis of combined pituitary hormone deficiencies

Pituitary gland commitment from oral ectoderm occurs in response to inductive signals from the neuroepithelium of the ventral diencephalon. Invagination of the oral ectoderm leads to the creation of Rathke's pouch. Intensified cell proliferation within Rathke's pouch results in formation of the anterior pituitary lobe. Subsequently, highly differentiated cell types arise sequentially due to overlapping, but distinct, spatial and temporal patterns of signaling molecules and transcription factors. Mutations in some of the pituitary-specific transcription factors have been identified in patients with hypopituitarism, confirming the role of these factors in pituitary development.

Cytochemical and molecular biological aspects of the pituitary and pituitary adenomas--cell differentiation and transcription factors

The anterior pituitary is composed of several cell types, each responsible for the production of specific hormones. Each hormone secreting cells is defined by the activation of its respective hormone genes in a temporally and spatially regulated manner. Recent development in cytochemistry and molecular biology have provided various aspects of human pituitary adenomas, i.e., functional differentiation and classification. The molecular factors that determine hormone production have now been identified as transcription factors. Many novel transcription factors that play a role in anterior pituitary development are implicated. In this review, we focus on the transcriptional factors roles on functional differentiation of the pituitary cells and adenomas and the contribution of cytochemistry and recent development in molecular biological techniques.

Cloning and Characterization of the Rat Gene Encoding GAP-43

GAP-43 is a gene expressed only in the nervous system. The protein product is believed to be important to neuronal growth and plasticity. Most, and likely all, neurons express high levels of GAP-43 during periods of neurite elongation. To initiate studies of GAP-43 gene regulation we have cloned the rat gene encoding GAP-43. The GAP-43 gene includes three exons. The first exon encodes only the amino terminal 10 amino acids, which corresponds to the membrane targeting domain of GAP-43. The second exon encodes a putative calmodulin binding domain and a protein kinase C phosphorylation site. The 5'-flanking sequence is unusual in that it lacks CAAT or TATA elements, and directs RNA transcription initiation from several sites. Some of the transcription start sites are used to a different degree in the central and peripheral nervous systems.

Hoxa 11 is upstream of Integrin alpha8 expression in the developing kidney

Mutation of the functionally redundant Hoxa 11/Hoxd 11 genes gives absent or rudimentary kidneys resulting from a dramatic reduction of the growth and branching of the ureteric bud. To understand better the molecular mechanisms of Hoxa 11/Hoxd 11 function in kidney development, it is necessary to identify the downstream target genes regulated by their encoded transcription factors. To this end, we conducted a screen for Hoxa 11-responsive genes in two kidney cell lines. HEK293 cells, which usually do not express Hoxa 11, were modified to allow inducible Hoxa 11 expression. The mK10 cells, derived specifically for this study from Hoxa 11/Hoxd 11 double-mutant mice, were also modified to give cell populations with and without Hoxa 11 expression. Differential display, Gene Discovery Arrays, and Affymetrix genechip probe arrays were used to screen for genes up- or down-regulated by Hoxa 11. Nine genes, PDGF A, Cathepsin L, annexin A1, Mm.112139, Est2 repressor factor, NrCAM, ZNF192, integrin-associated protein, and GCM1, showed reproducible 3-fold or smaller changes in gene expression in response to Hoxa 11. One gene, the Integrin alpha8, was up-regulated approximately 20-fold after Hoxa 11 expression. The Integrin alpha8 gene is expressed together with Hoxa 11 in metanephric mesenchyme cells, and mutation of Integrin alpha8 gives a bud-branching morphogenesis defect very similar to that observed in Hoxa 11/Hoxd 11 mutant mice. In situ hybridizations showed a dramatic regional reduction in Integrin alpha8 expression in the developing kidneys of Hoxa 11/Hoxd 11 mutant mice. This work suggests that the Integrin alpha8 gene may be a major effector of Hoxa 11/Hoxd 11 function in the developing kidney.

Cross-repression, a functional consequence of the physical interaction of non-liganded nuclear receptors and POU domain transcription factors

Nuclear receptors (NRs) and POU domain factors form two important transcription factor families for which several levels of functional interference have been described. In this study, the adopted orphan receptors constitutive androstane receptor (CAR) and pregnane X receptor (PXR) were found to perform direct protein-protein interactions with Pit-1, a representative POU domain factor. The ligand-dependent interaction profile of Pit-1 with CAR, PXR, and the vitamin D receptor in solution was shown to be that of a corepressor. In the absence of receptor agonist Pit-1 inhibited the complex formation of NRs with the retinoid X receptor on DNA. Also in living cells, Pit-1 and Oct-1, another POU domain factor, behaved like corepressors of NR signaling, and Pit-1-mediated repression was found to involve histone deacetylases. Conversely vitamin D receptor, CAR, and PXR were shown to act as repressors of Pit-1 signaling in different cell lines (MCF-7, HaCaT, and GH4C1). This repression was found to be independent of histone deacetylases and seems to be based on a competition of NRs with coactivator and corepressor proteins for overlaying interaction interfaces on the surface of Pit-1. Taken together this study suggests that cross-repression should occur in all tissues in which POU domain factors and non-liganded NRs meet each other.

Human placental growth hormone--a review

Placental growth hormone (PGH) is the product of the GH-V gene, predominantly expressed in the syncytiotrophoblast layer of the human placenta. PGH differs from pituitary growth hormone by 13 amino acids and possesses one glycosylation site. It has high somatogenic and low lactogenic activities. In the maternal circulation from 12-20 weeks up to term, PGH gradually replaces pituitary growth hormone, which becomes undetectable. PGH is secreted by the placenta in a non-pulsatile manner. This continuous secretion appears to have important implications for physiological adjustment to gestation and especially in the control of maternal IGF1 levels. PGH secretion is regulated in vitro and in vivo by glucose. Lower maternal levels of PGH are observed in pregnancies with fetal growth retardation. PGH is one example of a trophoblast hormone, which allows maternal metabolic adaptation to pregnancy. In addition, our recent data on its expression in invasive extravillous trophoblasts suggest that the physiological role of PGH might also include a direct influence of this hormone on placental development via an autocrine or paracrine mechanism.

Transcriptional regulation of the human PRL-releasing peptide (PrRP) receptor gene by a dopamine 2 Receptor agonist: cloning and characterization of the human PrRP receptor gene and its promoter region

PRL-releasing peptide receptor (PrRPR) mRNA was expressed in pituitary adenomas but was not detected in patients treated with bromocriptine, a specific agonist of dopamine 2 (D2) receptor. Although medical treatment with bromocriptine is effective for patients with pituitary adenomas, little is known about the molecular mechanisms of gene regulation mediated by D2 receptors. The cloned human PrRPR gene spanned approximately 2.0 kb and contained two exons and one intron. Two functional polyadenylation signals located at 510 and 714 bp downstream from the stop codon. A primer extension analysis demonstrated two major transcriptional start sites at 139 and 140 bp upstream from the translational start site and an additional minor site at -161. The promoter region contained several putative binding sites for transcriptional factors including pituitary-specific transcription factor (Pit 1), activator protein 1 (AP-1), and specificity protein (Sp1), but no typical TATA or CAAT box. This promoter showed the strong activity in the pituitary-derived GH4C1 cells, and the region between -697 and -596 bp was responsible for the stimulation both by forskolin and overexpression of cAMP response element binding protein (CREB). These stimulations were significantly suppressed by incubation with bromocriptine in a dose- and time-dependent manner, and the mutant CREB (S133A) completely abolished the inhibitory events of bromocriptine. However, EMSA studies demonstrated that CREB did not bind to this region, to which an approximately 60-kDa protein was strongly bound, and that antibodies against CREB, c-Fos, and Sp1 did not supershift this complex. Furthermore, the amount of this unknown protein was apparently reduced by treatment with bromocriptine. A series of mutation analyses demonstrated that the specific sequence, 5'-cccacatcat-3', was required for both the binding to the 60-kDa protein and the repression by bromocriptine. Therefore, the transcriptional repression of the PrRPR gene by bromocriptine required CREB but was independent of direct binding of CREB to the gene and that the sequence -663 -- -672, 5'-cccacatcat-3', bound to the 60-kDa protein appeared to be critical for this event.

A novel mutation in PIT-1: phenotypic variability in familial combined pituitary hormone deficiencies

Mutations in PIT-1 have been described in several cases of familial combined pituitary hormone deficiencies. This study describes a novel PIT-1 mutation that was found in two siblings of a highly consanguineous family of Israeli-Arab origin. The missense mutation (G688A) causes a lysine (K) to glutamic acid (E) substitution at codon 230. This codon resides in the first helix of the POU-homeodomain, which is directly involved in DNA binding. This amino acid is conserved in most homeodomain proteins, suggesting that the substitution disrupts the DNA-binding activity of the mutant protein. Two main observations are described: 1. The clinical presentation of the mutation involves intrauterine growth retardation. 2. One sibling had full deficency of growth hormone and thyroid stimulating hormone, whereas the other had only growth hormone deficiency. This is, to the best of our knowledge, a unique expression of a novel PIT-1 mutation.

Neonatal Meishan pigs show POU1F1 genotype effects on plasma GH and PRL concentration

Chinese Meishan pigs develop rapidly with onset of puberty at less than 100 days of age, and have a smaller placental size and larger litter size as compared with British/Continental breeds. POU1F1 is a member of the POU-domain family gene and is a positive regulator for growth hormone (GH), prolactin (PRL), and thyroid-stimulating hormone beta (TSHbeta) in several mammalian species. To investigate the role of POU1F1 in controlling pig growth and reproduction traits, Meishan (MS) pigs segregating a MspI POU1F1 polymorphism were used to determine differences of GH and PRL at both mRNA and circulating hormone concentrations. Animals from nine litters were used to collect pituitary (n=60) and/or blood samples (n=80) at day 0, 15, and 30 after birth, and all animals were genotyped (CC, CD, DD) for the MspI POU1F1 polymorphism. Reverse transcriptase-polymerase chain reaction (RT-PCR) with standard curve quantification was used to quantify mRNA levels for GH, PRL, and two alternative POU1F1 transcripts, POU1F1-alpha, and POU1F1-beta. Radioimmunoassays were done to determine the circulating concentration of GH and PRL in blood plasma. Our results indicated a significant effect of POU1F1 genotype on circulating levels of both GH and PRL at birth, but not thereafter. The DD neonates had lower levels of GH, but higher levels of PRL, than other genotypes. POU1F1-alpha mRNA decreased (P<0.05) from days 0 to 30, which paralleled decreases (P<0.05) in GH mRNA as well as PRL and GH plasma levels over the same period. POU1F1-beta mRNA levels did not significantly change over this period. Correlations were significant between POU1F1-alpha mRNA and both GH mRNA and GH plasma concentration levels, as well as between the two POU1F1 mRNA isoforms. Results from this study add to our understanding of the role of POU1F1 in controlling pig development and reproduction.

An ERK2 docking site in the Pointed domain distinguishes a subset of ETS transcription factors

The ETS transcription factors perform distinct biological functions despite conserving a highly similar DNA-binding domain. One distinguishing property of a subset of ETS proteins is a conserved region of 80 amino acids termed the Pointed (PNT) domain. Using enzyme kinetics we determined that the Ets-1 PNT domain contains an ERK2 docking site. The docking site enhances the efficiency of phosphorylation of a mitogen-activated protein kinase (MAPK) site N-terminal to the PNT domain. The site enhances ERK2 binding rather than catalysis. Three hydrophobic residues are involved in docking, and the previously determined NMR structure indicates that these residues are clustered on the surface of the Ets-1 PNT domain. The docking site function is conserved in the PNT domain of the highly related Ets-2 but not in the ets family member GABPalpha. Ablation of the docking site in Ets-1 and Ets-2 prevented Ras pathway-mediated enhancement of the transactivation function of these proteins. This study provides structural insight into the function of a MAPK docking site and describes a unique activity for the PNT domain among a subset of ets family members.

Role of transcription factors in the pathogenesis of pituitary adenomas: a review

The diversity inherent in every organ has its roots in gene-expression variation and is revealed through distinctions in the molecular profile and hence the identity of individual cell type. Study into the molecular mechanisms of the development of individual cell type within the pituitary, which is under the control of transcription factors, has provided a basis for a deeper insight into the molecular mechanisms underlying the pathogenesis of a variety of hormone-producing pituitary tumors. Identification of some of these transcription factors in pituitary adenomas further supports their role in the pathogenesis of pituitary adenomas. Understanding the molecular mechanisms of regulation of proliferation of pituitary cell types by transcription factors offers a basis for hope that rational genetic or pharmacologic therapies for pituitary tumors can be designed in the future.

Targeting oncogenesis by introduction of a 5.2-kbp segment of the 5' regulatory region of the human thyrotropin beta-subunit gene

We produced transgenic mice carrying a fusion gene (TTP-5) consisting of a 5.2-kbp segment of the 5' flanking sequence of the human thyrotropin beta-subunit (TSH beta) gene linked to the simian virus 40 large T antigen (SVT) gene. These mice developed pituitary tumors 6 months after birth and wasted away. With the 5.2-kbp TSH beta 5' flanking region governing SVT expression, SVT mRNA was present in the pituitary and testis but not in other tissues, as detected by the reverse transcriptase-polymerase chain reaction. Histological and immunohistochemical analyses showed that the pituitary tumors of the transgenic mice were composed of moderately differentiated pituitary cells that expressed TSH, growth hormone, and prolactin. These results indicate that the 5.2-kbp segment of the human TSH beta 5' regulatory region is sufficient to drive expression of SVT and induce tumorigenesis of hormone-producing pituitary cells in transgenic mice.

CCAAT/enhancer binding protein beta regulates expression of the cystatin-related epididymal spermatogenic (Cres) gene

The CRES protein is a member of the cystatin superfamily of cysteine protease inhibitors with restricted expression in stage-specific germ cells, proximal caput epididymidis, and anterior pituitary gonadotroph cells. To elucidate the molecular mechanisms regulating the highly restricted expression of the cres gene, we have sequenced 1.6 kilobases of mouse cres 5' flanking sequence and performed studies to examine the cres gene promoter. Two putative CCAAT/enhancer binding protein (C/EBP) transcription factor binding motifs exist within the first 135 base pairs of cres promoter. Furthermore, our studies demonstrate that cres mRNA levels are dramatically reduced in the epididymides of C/EBP beta-deficient mice. These data suggest that the C/EBP family of transcription factors, in particular C/EBP beta, plays a role in the regulation of cres gene expression. In support of this finding, Northern blot analysis showed that C/EBP beta is the predominant C/EBP family member expressed in the L beta T2 gonadotroph cell line and the proximal caput epididymidis. Also, gel shift and supershift assays demonstrated that C/EBP beta protein in nuclear extracts from L beta T2 gonadotroph cells and epididymal cells bound to the two C/EBP sites in the cres promoter. Finally, to test the in vivo function of the C/EBP sites in cres gene expression, transfection studies were performed in L beta T2 gonadotroph cells and two heterologous cell systems. These experiments showed a significant reduction of cres transactivation when either C/EBP sites were mutated, and no transC/EBP activation of the cres promoter when both C/EBP sites were mutated. Taken together, these studies demonstrate that the C/EBP beta transcription factor is necessary for high levels of cres gene expression in the proximal caput epididymidis and anterior pituitary gonadotroph cells.

Displacement of YY1 by differentiation-specific transcription factor hSkn-1a activates the P(670) promoter of human papillomavirus type 16

Transcription from human papillomavirus type 16 (HPV16) P(670), a promoter in the E7 open reading frame, is repressed in undifferentiated keratinocytes but becomes activated upon differentiation. We showed that the transient luciferase expression driven by P(670) was markedly enhanced in HeLa cells cotransfected with an expression plasmid for human Skn-1a (hSkn-1a), a transcription factor specific to differentiating keratinocytes. The hSkn-1a POU domain alone, which mediates sequence-specific DNA binding, was sufficient to activate the expression of luciferase. Electrophoretic mobility shift assay revealed the presence of two binding sites, sites 1 and 2, upstream of P(670), which were shared by hSkn-1a and YY1. Site 1 bound more strongly to hSkn-1a than site 2 did. YY1 complexing with a short DNA fragment having site 1 was displaced by hSkn-1a, indicating that hSkn-1a's affinity with site 1 was stronger than YY1's. Disrupting the binding sites by nucleotide substitutions raised the basal expression level of luciferase and decreased the enhancing effect of hSkn-1a. In HeLa cells transfected with circular HPV16 DNA along with the expression plasmid for hSkn-1a, the transcript from P(670) was detectable, which indicates that the results obtained with the reporter plasmids are likely to have mimicked the regulation of P(670) in authentic HPV16 DNA. The data strongly suggest that the transcription from P(670) is repressed primarily by YY1 binding to the two sites, and the displacement of YY1 by hSkn-1a releases P(670) from the repression.

Signaling and transcriptional mechanisms in pituitary development

During the development of the pituitary gland, distinct hormone-producing cell types arise from a common population of ectodermal progenitors, providing an instructive model system for elucidating the molecular mechanisms of patterning and cell type specification in mammalian organogenesis. Recent studies have established that the development of the pituitary occurs through multiple sequential steps, allowing the coordinate control of the commitment, early patterning, proliferation, and positional determination of pituitary cell lineages in response to extrinsic and intrinsic signals. The early phases of pituitary development appear to be mediated through the activities of multiple signaling gradients emanating from key organizing centers that give rise to temporally and spatially distinct patterns of transcription factor expression. The induction of these transcriptional mediators in turn acts to positionally organize specific pituitary cell lineages within an apparently uniform field of ectodermal progenitors. Ultimately, pituitary cell types have proven to be both specified and maintained through the combinatorial interactions of a series of cell-type-restricted transcription factors that dictate the cell autonomous programs of differentiation in response to the transient signaling events.

Thyrotropin-secreting pituitary adenomas. Clinical and biological heterogeneity and current treatment

Thyrotropin (TSH)-secreting pituitary adenomas represent about 1-2% of all pituitary adenomas and cause secondary or central hyperthyroidism. TSH-secreting adenomas are part of the syndrome of 'inappropriate secretion of TSH' (SITSH). The hormonal profile is characterized by nonsuppressed TSH in the presence of high levels of free thyroid hormones (FT3 and FT4). Previous reports have described the surgical cure of TSH adenoma to be more difficult than other functional adenomas because of large and invasive features. However, with the current introduction of ultrasensitive immunometric assays, TSH-secreting adenomas are more often recognized. Early diagnosis of TSH-secreting adenomas leads to a high rate of remission of hyperthyroidism after surgery. However, some of those type of adenomas have clinical heterogeneity, and subsequently cannot be cured by surgery alone. We present our experiences and review reported cases of TSH-secreting adenomas to direct current management.

Regulation of Pit-1 expression by ghrelin and GHRP-6 through the GH secretagogue receptor

GH secretagogues are an expanding class of synthetic peptide and nonpeptide molecules that stimulate the pituitary gland to secrete GH through their own specific receptor, the GH-secretagogue receptor. The cloning of the receptor for these nonclassical GH releasing molecules, together with the more recent characterization of an endogenous ligand, named ghrelin, have unambiguously demonstrated the existence of a physiological system that regulates GH secretion. Somatotroph cell-specific expression of the GH gene is dependent on a pituitary-specific transcription factor (Pit-1). This factor is transcribed in a highly restricted manner in the anterior pituitary gland. The present experiments sought to determine whether the synthetic hexapeptide GHRP-6, a reference GH secretagogue compound, as well as an endogenous ligand, ghrelin, regulate pit-1 expression. By a combination of Northern and Western blot analysis we found that GHRP-6 elicits a time- and dose-dependent activation of pit-1 expression in monolayer cultures of infant rat anterior pituitary cells. This effect was blocked by pretreatment with actinomycin D, but not by cycloheximide, suggesting that this action was due to direct transcriptional activation of pit-1. Using an established cell line (HEK293-GHS-R) that overexpresses the GH secretagogue receptor, we showed a marked stimulatory effect of GHRP-6 on the pit-1 -2,500 bp 5'-region driving luciferase expression. We truncated the responsive region to -231 bp, a sequence that contains two CREs, and found that both CREs are needed for GHRP-6-induced transcriptional activation in both HEK293-GHS-R cells and infant rat anterior pituitary primary cultures. The effect was dependent on PKC, MAPK kinase, and PKA activation. Increasing Pit-1 by coexpression of pCMV-pit-1 potentiated the GHRP-6 effect on the pit-1 promoter. Similarly, we showed that the endogenous GH secretagogue receptor ligand ghrelin exerts a similar effect on the pit-1 promoter. These data provide the first evidence that ghrelin, in addition to its previously reported GH-releasing activities, is also capable of regulating pit-1 transcription through the GH secretagogue receptor in the pituitary, thus giving new insights into the physiological role of the GH secretagogue receptor on somatotroph cell differentiation and function.

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.

Optimal Oct-2 affinity for an extended DNA site and the effect of GST fusion on site preference

The regulator of immunoglobulin expression Oct-2 and the related widely expressed transcription factor Oct-1 have been shown to interact with DNA sequences containing an "octamer" motif, ATGC(A/T)AAT. To better understand Oct-2 function we have used random oligonucleotide selection and competition assays to define the optimal recognition site for this protein. The selected site contains an extended sequence that is remarkably similar to octamer-heptamer sequences found in immunoglobulin heavy-chain regulatory sequences, and the affinity of Oct-2 for this site is at least 50-fold greater than for sites containing the octamer motif alone. Fusion to glutathione S-transferase, a widely used model for protein-DNA and protein-protein interaction, does not alter the optimal Oct-2 recognition site, but inhibits Oct-2 POU-domain dimerization, slows the dissociation rate of the GST-Oct-2/DNA complex, and increases the relative importance of the heptamer domain for Oct-2 binding. These data advance our ability to identify in vivo targets of POU-factor regulation and also suggest that GST-fusion proteins should be used with caution in DNA-binding studies.

The hSkn-1a POU transcription factor enhances epidermal stratification by promoting keratinocyte proliferation

Skn-1a is a POU transcription factor that is primarily expressed in the epidermis and is known to modulate the expression of several genes associated with keratinocyte differentiation. However, the formation of a stratified epidermis requires a carefully controlled balance between keratinocyte proliferation and differentiation, and a role for Skn-1a in this process has not been previously demonstrated. Here, our results show, surprisingly, that human Skn-1a contributes to epidermal stratification by primarily promoting keratinocyte proliferation and secondarily by enhancing the subsequent keratinocyte differentiation. In organotypic raft cultures of both primary human keratinocytes and immortalized HaCaT keratinocytes, human Skn-1a expression is associated with increased keratinocyte proliferation and re-epithelialization of the dermal substrates, resulting in increased numbers of keratinocytes available for the differentiation process. In these same raft cultures, human Skn-1a expression enhances the phenotypic changes of keratinocyte differentiation and the upregulated expression of keratinocyte differentiation genes. Conversely, expression of a dominant negative human Skn-1a transcription factor lacking the C-terminal transactivation domain blocks keratinocytes from proliferating and stratifying. Keratinocyte stratification is dependent on a precise balance between keratinocyte proliferation and differentiation, and our results suggest that human Skn-1a has an important role in maintaining epidermal homeostasis by promoting keratinocyte proliferation.

Stage-sensitive blockade of pituitary somatomammotrope development by targeted expression of a dominant negative epidermal growth factor receptor in transgenic mice

The epidermal growth factor receptor (EGFR) and its ligands EGF and transforming growth factor-alpha (TGF alpha) are expressed in the anterior pituitary, and overexpression of TGF alpha in the lactotrope cells of the pituitary gland in transgenic mice results in lactotrope hyperplasia and adenomata, suggesting a role for EGFR signaling in pituitary cell proliferation. To address the role of EGFR signaling in pituitary development in vivo, we blocked EGFR signaling in transgenic mice using the dominant negative properties of a mutant EGFR lacking an intracellular protein kinase domain (EGFR-tr). We directed EGFR-tr expression to GH- and PRL- producing cells using GH and PRL promoters, and a tetracycline-inducible gene expression system, to allow temporal control of gene expression. EGFR-tr overexpression in GH-producing cells during embryogenesis resulted in dwarf mice with pituitary hypoplasia. Both somatotrope and lactotrope development were blocked. However, when EGFR-tr overexpression was delayed to the postnatal period either by directing its expression with the PRL promoter or by delaying the onset of induction with tetracycline in the GH cells, no specific phenotype was observed. Lactotrope hyperplasia during pregnancy also occurred normally in the PRL-EGFR-tr mice. These data suggest that EGFR signaling is required for the differentiation and/or maintenance of somatomammotropes early in pituitary organogenesis but not later in life. (Molecular Endocrinology 15: 600-613, 2001)

A pituitary cell-restricted T box factor, Tpit, activates POMC transcription in cooperation with Pitx homeoproteins

The pituitary gland has provided unique insight into molecular mechanisms and regulatory factors controlling both differentiation and gene transcription. We identified Tpit, a novel T box factor only present in the two pituitary POMC-expressing lineages, the corticotrophs and melanotrophs, and apparently in no other tissue, including hypothalamic POMC neurons. In pituitary cells, Tpit activation of POMC gene transcription requires cooperation with Pitx1, the two factors binding to contiguous sites within the same regulatory element. In gain-of-function experiments, Tpit induces POMC expression in undifferentiated pituitary cells, indicating that it can initiate differentiation into POMC-expressing lineages. TPIT gene mutations were found in patients with isolated deficiency of pituitary POMC-derived ACTH, in support of an essential role of Tpit for differentiation of the pituitary POMC lineage.

Regulation of ectodermal and excretory function by the C. elegans POU homeobox gene ceh-6

Caenorhabditis elegans has three POU homeobox genes, unc-86, ceh-6 and ceh-18. ceh-6 is the ortholog of vertebrate Brn1, Brn2, SCIP/Oct6 and Brn4 and fly Cf1a/drifter/ventral veinless. Comparison of C. elegans and C. briggsae CEH-6 shows that it is highly conserved. C. elegans has only three POU homeobox genes, while Drosophila has five that fall into four families. Immunofluorescent detection of the CEH-6 protein reveals that it is expressed in particular head and ventral cord neurons, as well as in rectal epithelial cells, and in the excretory cell, which is required for osmoregulation. A deletion of the ceh-6 locus causes 80% embryonic lethality. During morphogenesis, embryos extrude cells in the rectal region of the tail or rupture, indicative of a defect in the rectal epithelial cells that express ceh-6. Those embryos that hatch are sick and develop vacuoles, a phenotype similar to that caused by laser ablation of the excretory cell. A GFP reporter construct expressed in the excretory cell reveals inappropriate canal structures in the ceh-6 null mutant. Members of the POU-III family are expressed in tissues involved in osmoregulation and secretion in a number of species. We propose that one evolutionary conserved function of the POU-III transcription factor class could be the regulation of genes that mediate secretion/osmoregulation.

A member of the nuclear factor-1 family is involved in the pituitary repression of the human placental growth hormone genes

The human growth hormone (GH) gene family consists of five tandemly arranged and highly related genes, including the chorionic somatomammotropins (CSs), at a single locus on chromosome 17. Despite striking homologies in promoter and flanking DNA sequences, the genes within this locus have different tissue-specific patterns of expression: GH-N is expressed almost exclusively in the somatotrophs of the anterior pituitary; the remaining genes, including CS-A, are expressed in placental syncytiotrophoblast. Previously we proposed that active repression of the placental gene promoters in pituitary GC cells is mediated by upstream 'P' sequences and, specifically, a 263 bp region containing two 'P' sequence elements (PSE-A and PSE-B) and corresponding factors (PSF-A and PSF-B). We have now examined the possibility that PSF-A and PSF-B are members of the nuclear factor (NF)-1 family. Transcripts of NF-1A, NF-1C and NF-1X, but not of NF-1B, were readily detected in GC cells. High-affinity binding of NF-1 to PSE-B, but not to PSE-A, was confirmed by competition of DNA-protein interactions by using NF-1 DNA elements and antibodies. Functionally, a NF-1 element was able to substitute for PSE-B as a promoter-specific repressor in GC cells after gene transfer. However, there was a difference in the magnitude of repression exerted by the NF-1 and PSF-B elements on the CS-A promoter and, with the use of mutations, this difference was shown to be consistent with variations in NF-1-binding sequences. These results indicate that PSF-B, but not PSF-A, is a member of the NF-1 family, which participates in the PSF complex and in the repression of the CS-A promoter in pituitary GC cells.

POU domain factors in the neuroendocrine system: lessons from developmental biology provide insights into human disease

POU domain factors are transcriptional regulators characterized by a highly conserved DNA-binding domain referred to as the POU domain. The structure of the POU domain has been solved, facilitating the understanding of how these proteins bind to DNA and regulate transcription via complex protein-protein interactions. Several members of the POU domain family have been implicated in the control of development and function of the neuroendocrine system. Such roles have been most clearly established for Pit-1, which is required for formation of somatotropes, lactotropes, and thyrotropes in the anterior pituitary gland, and for Brn-2, which is critical for formation of magnocellular and parvocellular neurons in the paraventricular and supraoptic nuclei of the hypothalamus. While genetic evidence is lacking, molecular biology experiments have implicated several other POU factors in the regulation of gene expression in the hypothalamus and pituitary gland. Pit-1 mutations in humans cause combined pituitary hormone deficiency similar to that found in mice deleted for the Pit-1 gene, providing a striking example of how basic developmental biology studies have provided important insights into human disease.

Effect of estradiol and FBS on PRL cells, GH cells, and PRL/GH cells in primary cultures of pituitary cells from prenatal rats

The effects of estradiol (E2) treatment on prolactin (PRL) cells, GH cells, and PRL/GH cells in immature pituitary cells were determined using primary cultures from prenatal rats and immunocytochemistry with fluorescent antibodies. Anterior pituitaries obtained from fetuses on day 22 of pregnancy were monodispersed and cultured in chemically defined medium or medium containing 10% fetal bovine serum (FBS). After pre-incubation for 24 hr, E2 (final concentrations were 0 M, 10(-8) M, 10(-7) M, and 10(-6) M) was added into each medium. After 72 hr of incubation, cells were subjected to immunocytochemistry. E2 stimulated the increase of PRL cells in a dose-dependent manner, and the PRL cell percentage cultured with FBS in all groups was significantly higher than that cultured in chemically-defined medium. PRL/GH cells also responded to E2 in the same manner as PRL cells. E2 was not effective in proliferating GH cells, and GH cell percentage significantly decreased with the addition of FBS into the medium. These results suggest that E2 is dose-dependently capable of increasing immature PRL cells and/or PRL/GH cells in vitro. Moreover, there is a factor(s) in FBS that regulates the increase of these cells.

Pituitary and extrapituitary growth hormone: Pit-1 dependence?

Growth hormone (GH) is primarily produced in pituitary somatotrophs. The synthesis of this hormone is thought to be dependent upon a pituitary-specific transcription factor (Pit-1). However, many extrapituitary tissues are now known to express GH genes. The extrapituitary production of GH may therefore indicate an extrapituitary distribution of the Pit-1 gene. The extrapituitary production of GH may, alternatively, indicate that GH expression occurs independently of Pit-1 in extrapituitary tissues. These possibilities are considered in this brief review.Key words: growth hormone, pituitary, pituitary transcription factor 1.

Retinoic acids and thyroid hormone act synergistically with dexamethasone to increase growth hormone-releasing hormone receptor messenger ribonucleic acid expression

The effects of all-trans-retinoic acid (RA), 9-cis-retinoic acid (9cRA), and thyroid hormone (T3) on GH-releasing hormone receptor (GHRH-R) messenger RNA (mRNA) expression were studied using ribonuclease protection assay in the fetal rat pituitary gland and in MtT/S cells, a clonal GH cell line derived from an estrogen-induced somatotropic tumor in the rat. Although RA (1 microM), 9cRA (1 microM), or T3 (1 nM) alone showed little effect on GHRH-R mRNA expression in the MtT/S cells, each of these substances was found to act synergistically with dexamethasone (DEX; 500 nM) to increase GHRH-R mRNA expression. The effects of RAs and T3 were dose dependent, with maximum effects observed at 1 microM and 1 nM, respectively. The maximum effect of RAs or T3 was not further augmented by the addition of T3 or RAs, respectively. No apparent differences were observed in this study between the actions of RA and 9cRA. The Northern analyses showed that MtT/S cells express retinoic acid receptor alpha2 mRNA and thyroid hormone receptor beta2 mRNA, and DEX did not affect the levels of these mRNAs. This suggests that the role of DEX in enabling RAs or T3 to up-regulate GHRH-R mRNA levels is not an induction of the expression of each specific receptor for RAs and T3. The similar enhancement of DEX induction of GHRH-R mRNA by RAs or T3 was also observed in the fetal rat pituitary gland in culture, suggesting that RA and/or T3 is involved in the mechanisms responsible for the developmentally regulated expression of GHRH-R mRNA.

Allosteric effects of Pit-1 DNA sites on long-term repression in cell type specification

Reciprocal gene activation and restriction during cell type differentiation from a common lineage is a hallmark of mammalian organogenesis. A key question, then, is whether a critical transcriptional activator of cell type-specific gene targets can also restrict expression of the same genes in other cell types. Here, we show that whereas the pituitary-specific POU domain factor Pit-1 activates growth hormone gene expression in one cell type, the somatotrope, it restricts its expression from a second cell type, the lactotrope. This distinction depends on a two-base pair spacing in accommodation of the bipartite POU domains on a conserved growth hormone promoter site. The allosteric effect on Pit-1, in combination with other DNA binding factors, results in the recruitment of a corepressor complex, including nuclear receptor corepressor N-CoR, which, unexpectedly, is required for active long-term repression of the growth hormone gene in lactotropes.

Complementary DNA cloning and ontogenic expression of pituitary-specific transcription factor of chickens (Gallus domesticus) from the pituitary gland

Pit-1 is a pituitary-specific POU-domain DNA binding factor, which binds to and transactivates promoters of growth hormone (GH)-, prolactin (PRL)-, and thyroid-stimulating hormone-beta (TSHbeta)-encoding genes. Pit-1 has been identified in several mammalian species. In birds, it has been identified only in the turkey and chicken pituitary. Several (gg) Pit-1 cDNA sequences have been identified in the anterior pituitary of the chicken (Gallus domesticus). As in turkey, three different transcripts (ggPit-1*, ggPit-1beta*, and ggPit-1W*) of the Pit-1 gene were identified. This suggests that the chicken pituitary expresses more variants than reported earlier. Previous studies have concentrated on expressions during posthatch life of the turkey and chicken. The present study has determined the ontogeny of Pit-1 during the embryonic life of the chicken (day 1-day 21 of incubation). The mRNA for Pit-1 was first detected in the pituitary on day 5 of embryonic life. The expression of the mRNA was maintained until hatch. The presence of Pit-1 at this stage of embryonic development suggests that Pit-1 may be physiologically important during embryonic development of birds, as it precedes the gene expression and secretion of GH, PRL, and TSHbeta. A similar sequence for the expression of Pit-1 relative to GH and PRL during embryonic/fetal development has been reported for rodents.

Idiopathic growth hormone deficiency: a vanishing diagnosis?

Some non-organic causes for growth hormone (GH) deficiency (GHD) can be attributed to genetic defects within the hypothalamo-pituitary axis. Using modern molecular biology techniques micromutations within the GH and GH-releasing hormone receptor genes have been detected as a rare cause of isolated GHD. Combined pituitary hormone deficiencies (CPHD), on the other hand, are associated with defects that manifest during the organogenesis of the anterior pituitary gland. In recent years an increasing number of patients with CPHD has been reported, showing mutations within pituitary transcription factors Pit-1, Prop-1 and HesX1. Such defects can be observed with different frequencies in patients. Some disorders, such as CPHD due to Pit-1 mutations, display a hormonal phenotype that seems more or less invariable. In most other forms of genetic CPHD both the combination and severity of anterior pituitary hormone deficiencies vary considerably. Ongoing research concentrates on factors involved in the differentiation and proliferation of cells that belong to the hypothalamo-pituitary growth axis. As not every possible candidate turns out to be a frequent cause of GHD or CPHD in humans, it will be many more years before the term 'idiopathic' becomes a vanishing attribute to the clinical diagnosis of pituitary insufficiency.

The molecular basis of hypopituitarism

Pit-1 is a pituitary-specific transcription factor responsible for pituitary development and hormone expression in mammals. My laboratory and others have recently described several patients with combined pituitary hormone deficiency (CPHD) due to point mutations in the pit-1 gene. In addition to pit-1, other nuclear factors appear to be necessary for full expression of pituitary genes. A zinc finger transcription factor, Zn-15, is responsible with pit-1 for synergistic activation of the GH gene. The Pr1 gene is regulated synergistically by pit-1 and the estrogen receptor. Finally, the pit-1 gene itself is regulated by an enhancer element located > 10 kb upstream of the transcriptional start. This element contains several pit-1 DNA binding sites and retinoic acid response elements (RAREs). On one of these elements, pit-1 and RAR interact functionally to mediate a synergistic response to RA. Recent data from our laboratory suggests that RA induction of the pit-1 gene can be impaired by pit-1 gene mutations. Study of pit-1 mutations and their diverse pathophysiological mechanisms should increase our understanding of anterior pituitary gland development and gene regulation in normal and disease states.

The virtuoso of versatility: POU proteins that flex to fit

During the evolution of eukaryotes, a new structural motif arose by the fusion of genes encoding two different types of DNA-binding domain. The family of transcription factors which contain this domain, the POU proteins, have come to play essential roles not only in the development of highly specialised tissues, such as complex neuronal systems, but also in more general cellular housekeeping. Members of the POU family recognise defined DNA sequences, and a well-studied subset have specificity for a motif known as the octamer element which is found in the promoter region of a variety of genes. The structurally bipartite POU domain has intrinsic conformational flexibility and this feature appears to confer functional diversity to this class of transcription factors. The POU domain for which we have the most structural data is from Oct-1, which binds an eight base-pair target and variants of this octamer site. The two-part DNA-binding domain partially encircles the DNA, with the sub-domains able to assume a variety of conformations, dependent on the DNA element. Crystallographic and biochemical studies have shown that the binary complex provides distinct platforms for the recruitment of specific regulators to control transcription. The conformability of the POU domain in moulding to DNA elements and co-regulators provides a mechanism for combinatorial assembly as well as allosteric molecular recognition. We review here the structure and function of the diverse POU proteins and discuss the role of the proteins' plasticity in recognition and transcriptional regulation.

Expression of pituitary homeo box 1 (Ptx1) in human non-neoplastic pituitaries and pituitary adenomas

We investigated the localization of pituitary homeo box 1 (Ptx1) protein in five human non-neoplastic pituitaries and 73 of all types of pituitary adenomas using immunohistochemistry, and the expression of Ptx1 messenger RNA (mRNA) in 18 representative pituitary adenomas using the reverse transcriptase polymerase chain reaction (RT-PCR) technique. By immunohistochemical analysis, Ptx1 protein was extensively detected in the nuclei of normal human pituitary cells. Ptx1 was detected in 10/14 (71.4%) of growth hormone (GH)-secreting adenomas, 12/12 (100%) of prolactin (PRL)-secreting adenomas, 18/20 (90%) of adrenocorticotropic hormone (ACTH)-secreting adenomas, 6/7 (85.7%) of thyroid-stimulating hormone (TSH)-secreting adenomas, and 17/20 (85%) of clinically non-functioning adenomas, including 9/10 (90%) of gonadotropin-subunit-positive adenomas. Thus, there was no relationship between Ptx1 expression and a particular type of pituitary adenomas. By RT-PCR analysis, Ptx1 mRNA was expressed in all 18 cases of pituitary adenomas, including two cases negative for Ptx1 protein by immunohistochemistry. These results suggested that Ptx1 may be an universal transcription factor in both neoplastic and non-neoplastic conditions in human pituitaries. The synergistic action with other transcription factors may be speculated to determine the specific production of the anterior pituitary hormones.

Molecular genetic classification of central nervous system malformations

Traditional schemes of classifying nervous system malformations are based on descriptive morphogenesis of anatomic processes of ontogenesis, such as neurulation, neuroblast migration, and axonal pathfinding. This proposal is a first attempt to incorporate the recent molecular genetic data that explain programming of development etiologically. A scheme based purely on genetic mutations would not be practical, in part because only in a few dysgeneses are the specific defects known, but also because several genes might be involved sequentially and many genes inhibit or augment the expression of others. The same genes serve different functions at different stages and are involved in multiple organ systems. Some complex malformations, such as holoprosencephaly, result from several unrelated defective genes. Finally, a pure genetic classification would be too inflexible to incorporate some anatomic criteria. The basis for the proposed scheme is, therefore, disturbances in patterns of genetic expression; polarity gradients of the axes of the neural tube (eg, upregulation or downregulation of genetic influences); segmentation (eg, deletions of specific neuromeres, ectopic expression); mutations that cause change in cell lineage (eg, dysplastic gangliocytoma of cerebellum, myofiber differentiation within brain); and specific genes or molecules that mediate neuroblast migration in its early (eg, filamin-1), middle (eg, LIS1, double-cortin), or late course (eg, reelin, L1-CAM). The proposed scheme undoubtedly will undergo many future revisions, but it provides a starting point using currently available data.

Cloning and characterization of the 5'-flanking region of the human prolactin-releasing peptide receptor gene

Recently a novel peptide which specifically stimulates the secretion of prolactin (PRL) was found and named PRL-releasing peptide (PrRP). To evaluate the regulation of human (h) PrRP-receptor (PrRP-R) gene expression, we cloned the 5'-flanking region of the hPrRP-R gene and determined the nucleotide sequence of 4.0 kilobase pairs (kb) upstream from the translation start site. Analysis of the hPrRP-R transcripts by means of 5'-rapid amplification of cDNA ends suggested that the hPrRP-R gene had multiple transcription start sites between -429 and -365 from the translation start site. There is no typical TATA or CAAT but a GC box and putative binding sites for several transcription factors including Pit-1 and pituitary homeobox 1 (Ptx1). However, transient transfection studies using a luciferase reporter gene demonstrated that 5'-flanking region exerts promoter activity in several non-pituitary cell lines as well as in GH(3) cells. The GC box located from -467 to -457 was identified as an important region for the basal expression of the hPrRP-R gene. Knowledge of the promoter region of the hPrRP-R gene, which was obtained in the present study, will facilitate the clarification of its transcriptional regulation.