A novel E250X mutation of the PIT1 gene in a patient with combined pituitary hormone deficiency

POU1F1/Pou1f1 c.143-83A > G Variant Disrupts the Branch Site in Pre-mRNA and Leads to Dwarfism

POU Class 1 Homeobox1 (POU1F1/Pou1f1) is a well-established pituitary-specific transcription factor, and causes, when mutated, combined pituitary hormone deficiency in humans and mice. POU1F1/Pou1f1 has 2 isoforms: the alpha and beta isoforms. Recently, pathogenic variants in the unique coding region of the beta isoform (beta domain) and the intron near the exon-intron boundary for the beta domain were reported, although their functional consequences remain obscure. In this study, we generated mice carrying the Pou1f1 c.143-83A>G substitution that recapitulates the human intronic variant near the exon-intron boundary for the beta domain. Homozygous mice showed postnatal growth failure, with an average body weight that was 35% of wild-type littermates at 12 weeks, which was accompanied by anterior pituitary hypoplasia and deficiency of circulating insulin-like growth factor 1 and thyroxine. The results of RNA-seq analysis of the pituitary gland were consistent with reduction of somatotrophs, and this was confirmed immunohistochemically. Reverse transcription polymerase chain reaction of pituitary Pou1f1 mRNA showed abnormal splicing in homozygous mice, with a decrease in the alpha isoform, an increase in the beta isoform, and the emergence of the exon-skipped transcript. We further characterized artificial variants in or near the beta domain, which were candidate positions of the branch site in pre-mRNA, using cultured cell-basis analysis and found that only c.143-83A>G produced transcripts similar to the mice model. Our report is the first to show that the c.143-83A>G variant leads to splicing disruption and causes morphological and functional abnormalities in the pituitary gland. Furthermore, our mice will contribute understanding the role of POU1F1/Pou1f1 transcripts in pituitary development.

A Novel Splice-Site Deletion in the POU1F1 Gene Causes Combined Pituitary Hormone Deficiency in Multiple Sudanese Pedigrees

Pathogenic variants within the gene encoding the pituitary-specific transcription factor, POU class 1 homeobox 1 (POU1F1), are associated with combined pituitary hormone deficiency (CPHD), including growth hormone, prolactin, and thyrotropin stimulating hormone deficiencies. The aim of the study was to identify genetic aetiology in 10 subjects with CPHD from four consanguineous Sudanese families. Medical history, as well as hormonal and radiological information, was obtained from participants’ medical records. Targeted genetic analysis of the POU1F1 gene was performed in two pedigrees with a typical combination of pituitary deficiencies, using Sanger sequencing, and whole-exome sequencing was performed in the other two pedigrees, where hypocortisolism and additional neurologic phenotypes were also initially diagnosed. In POU1F1 gene (NM_001122757.2) a novel homozygous splice-site deletion—namely, c.744-5_749del—was identified in all 10 tested affected family members as a cause of CPHD. Apart from typical pituitary hormonal deficiencies, most patients had delayed but spontaneous puberty; however, one female had precocious puberty. Severe post-meningitis neurologic impairment was observed in three patients, of whom two siblings had Dyke–Davidoff–Masson syndrome, and an additional distantly related patient suffered from cerebral infarction. Our report adds to the previously reported POU1F1 gene variants causing CPHD and emphasises the importance of genetic testing in countries with high rates of consanguineous marriage such as Sudan. Genetic diagnostics elucidated that the aetiologies of hypopituitarism and brain abnormalities, identified in a subset of affected members, were separate. Additionally, as central hypocortisolism is not characteristic of POU1F1 deficiency, hydrocortisone replacement therapy could be discontinued. Elucidation of a genetic cause, therefore, contributed to the more rational clinical management of hypopituitarism in affected family members.

POU1F1 mutations in combined pituitary hormone deficiency: differing spectrum of mutations in a Western-Indian cohort and systematic analysis of world literature

CONTEXT

POU1F1 mutations are prevalent in Indian CPHD cohorts. Genotype-phenotype correlation is not well-studied.

AIM

To describe phenotypic and genotypic spectrum of POU1F1 mutations in our CPHD cohort and present systematic review as well as genotype-phenotype analysis of all mutation-positive cases reported in world literature.

METHODS

Retrospective study of POU1F1 mutation-positive patients from a western-Indian center. PRISMA guidelines based pubmed search of published literature of all mutation-positive patients.

RESULTS

Our cohort had 15 POU1F1 mutation-positive patients (9 index, 6 relatives). All had severe GH, TSH and prolactin deficiencies (GHD, TSHD and PD). TSHD was diagnosed earliest followed by GHD (median ages: TSHD-6 months, GHD-3 years), while PD was more variable. Two sisters had central precocious puberty at 7 years of age. Pubic hair was deficient in all post-pubertal patients (females: P1-P2, males: P3-P4). Splice-site/intronic/frameshift mutations were most common, while missense/nonsense mutations were less frequent (33%). Review of world literature yielded 114 patients (82 index patients) from 58 studies. GHD was present in all patients. TSHD was spared in 12.5% and PD in 4.4% patients. Missense/nonsense mutations accounted for 75% of spectrum. Phenotype-genotype analysis revealed higher mean peak-GH levels (1.1 vs 0.2 ng/ml, p = 0.008) and lower prevalence of anterior-pituitary hypoplasia (63.6% vs 86.3%, p = 0.03) in patients with heterozygous than homozygous and compound heterozygous mutations.

CONCLUSIONS

We present largest series of POU1F1 mutation-positive patients. Precocious puberty and defective pubarche are lesser-appreciated phenotypic features. Our mutation spectrum is different from that of world literature. Patients with heterozygous mutations have milder phenotype.

Extreme Short Stature and Severe Neurological Impairment in a 17-Year-Old Male With Untreated Combined Pituitary Hormone Deficiency Due to POU1F1 Mutation

Background: POU1F1 is an essential transcription factor for the differentiation, proliferation and survival of somatotrophs, lactotrophs, and thyrotrophs. Mutations in the POU1F1 gene are characterized by growth hormone (GH), thyrotropin, and prolactin deficiencies, commonly presenting with growth retardation and central hypothyroidism. Since the first report in 1992, more than 25 mutations have been identified in POU1F1. Case Description: We describe a 17-year-old male who presented to our Pediatric Endocrinology clinic with extreme short stature (height 81.7 cm, -9.3 SD), cognitive impairment, deaf-mutism, and neurological disabilities. L-thyroxine supplemental therapy, which had been initiated at the age of 6 months but ceased due to non-compliance, was reintroduced at presentation. GH therapy was initiated at 19 years of age, resulting in 42 cm linear growth, to a final height of 124 cm. Sequencing of POU1F1 revealed a previously described homozygous insertion mutation-c.580_581insT, p (Thr194Ilefs^*7)-in exon 4 causing a frameshift that introduces a stop codon 7 amino acids downstream, leading to a severely truncated protein lacking the homeodomain. Conclusion: This case report sheds light on the natural history of untreated patients with POU1F1 mutations and raises awareness for early diagnosis and adequate treatment of central congenital hypothyroidism and GH deficiency.

Genetic causes of isolated and combined pituitary hormone deficiency

Research over the last 20 years has led to the elucidation of the genetic aetiologies of Isolated Growth Hormone Deficiency (IGHD) and Combined Pituitary Hormone Deficiency (CPHD). The pituitary plays a central role in growth regulation, coordinating the multitude of central and peripheral signals to maintain the body's internal balance. Naturally occurring mutation in humans and in mice have demonstrated a role for several factors in the aetiology of IGHD/CPHD. Mutations in the GH1 and GHRHR genes shed light on the phenotype and pathogenesis of IGHD whereas mutations in transcription factors such as HESX1, PROP1, POU1F1, LHX3, LHX4, GLI2 and SOX3 contributed to the understanding of CPHD. Depending upon the expression patterns of these molecules, the phenotype may consist of isolated hypopituitarism, or more complex disorders such as septo-optic dysplasia (SOD) and holoprosencephaly. Although numerous monogenic causes of growth disorders have been identified, most of the patients with IGHD/CPHD remain with an explained aetiology as shown by the relatively low mutation detection rate. The introduction of novel diagnostic approaches is now leading to the disclosure of novel genetic causes in disorders characterized by pituitary hormone defects.

Genetic regulation of pituitary gland development in human and mouse

Normal hypothalamopituitary development is closely related to that of the forebrain and is dependent upon a complex genetic cascade of transcription factors and signaling molecules that may be either intrinsic or extrinsic to the developing Rathke's pouch. These factors dictate organ commitment, cell differentiation, and cell proliferation within the anterior pituitary. Abnormalities in these processes are associated with congenital hypopituitarism, a spectrum of disorders that includes syndromic disorders such as septo-optic dysplasia, combined pituitary hormone deficiencies, and isolated hormone deficiencies, of which the commonest is GH deficiency. The highly variable clinical phenotypes can now in part be explained due to research performed over the last 20 yr, based mainly on naturally occurring and transgenic animal models. Mutations in genes encoding both signaling molecules and transcription factors have been implicated in the etiology of hypopituitarism, with or without other syndromic features, in mice and humans. To date, mutations in known genes account for a small proportion of cases of hypopituitarism in humans. However, these mutations have led to a greater understanding of the genetic interactions that lead to normal pituitary development. This review attempts to describe the complexity of pituitary development in the rodent, with particular emphasis on those factors that, when mutated, are associated with hypopituitarism in humans.

A novel recessive splicing mutation in the POU1F1 gene causing combined pituitary hormone deficiency

BACKGROUND

Mutations in the gene encoding the pituitary transcription factor POU1F1 (Pit-1, pituitary transcription factor-1) have been described in combined pituitary hormone deficiency (CPHD).

AIM

The aim of this study was the characterisation of the molecular defect causing CPHD in a patient born to consanguineous parents.

SUBJECT AND METHODS

The case of a 12.5-yr-old girl presenting with severe growth failure at diagnosis (-3 SD score at 3 months) and deficiency of GH, PRL, and TSH was investigated for the presence of POU1F1 gene mutations by denaturing high performance liquid chromatography analysis.

RESULTS

A novel mutation adjacent to the IVS2 splicing acceptor site (IVS2-3insA) was identified in the patient at the homozygous state. Analysis of patient's lymphocyte mRNA and an in vitro splicing assay revealed the presence of 2 aberrant splicing products: a) deletion of the first 71 nucleotides of exon 3, altering the open reading frame and generating a premature stop codon, b) total exon 3 skipping resulting in an in frame deleted mRNA encoding a putative protein lacking part of the transactivation domain and of the POUspecific homeodomain. Notably, the patient's relatives heterozygous for the mutation had PRL levels under the normal range with no evident clinical symptoms.

CONCLUSIONS

The IVS2- 3insAmutation, responsible for CPHD at the homozygous state, causes the presence of 2 aberrant splicing products encoding non-functional products. In the heterozygotes one normal allele might not guarantee a complete pituitary function.

OTX2 mutation in a patient with anophthalmia, short stature, and partial growth hormone deficiency: functional studies using the IRBP, HESX1, and POU1F1 promoters

CONTEXT

OTX2 is a transcription factor gene essential for eye development. Although recent studies suggest the involvement of OTX2 in pituitary function, there is no report demonstrating a positive role of OTX2 in the pituitary function.

OBJECTIVE

The objective of the study was to report the results of functional studies indicating the relevance of OTX2 to pituitary function.

PATIENT

A Japanese female patient with bilateral anophthalmia was found to have short stature (height, -3.3 sd) and isolated partial GH deficiency (peak serum GH 3.1 and 9.7 mug/liter after insulin and arginine stimulations, respectively; serum IGF-I 37 ng/ml) at 3 yr 9 months of age. Magnetic resonance imaging delineated apparently normal pituitary gland.

RESULTS

Mutation analysis showed a de novo heterozygous frameshift mutation (c.402insC) that is predicted to retain the homeodomain but lose the transactivation domain. Functional studies revealed that the wild-type and mutant OTX2 proteins localized to the nucleus and bound to the target sequences within the IRBP (interstitial retinoid-binding protein), HESX1 (HESX homeobox 1), and POU1F1 promoters. Furthermore, the wild-type OTX2 protein markedly transactivated the promoters of IRBP ( approximately 27-fold), HESX1 ( approximately 4.5-fold), and POU1F1 ( approximately 19-fold), whereas the mutant OTX2 protein barely retained the transactivation activities and had no dominant-negative effects.

CONCLUSIONS

The results provide direct evidence for OTX2 being involved in the pituitary function. It is likely that the heterozygous severe OTX2 loss-of-function mutation caused GH deficiency and short stature, primarily because of decreased transactivation function for HESX1 and POU1F1.

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.

The role of transcription factors implicated in anterior pituitary development in the aetiology of congenital hypopituitarism

The anterior pituitary gland is a central regulator of growth, reproduction and homeostasis, and is the end-product of a carefully orchestrated pattern of expression of signalling molecules and transcription factors leading to the development of this complex organ secreting six hormones from five different cell types. Naturally occurring and transgenic murine models have demonstrated a role for many of these molecules in the aetiology of combined pituitary hormone deficiency (CPHD). These include the transcription factors HESX1, PROP1, POU1FI, LHX3, LHX4, TBX19 (TPIT), SOX3 and SOX2. The expression pattern of these transcription factors, their interaction with co-factors and their impact on target genes dictate the phenotype that results when the gene encoding the relevant transcription factor is mutated. The highly variable phenotype may consist of isolated hypopituitarism, or more complex disorders such as septo-optic dysplasia (SOD) and holoprosencephaly. Since mutations in any one transcription factor are uncommon, and since the overall incidence of mutations in known transcription factors is low in patients with CPHD, it is clear that many genes remain to be identified, and characterization of these will further elucidate the pathogenesis of these complex conditions, and also shed light on normal pituitary development.

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.

Pituitary hormone deficiencies due to transcription factor gene alterations

Mechanisms that control pituitary development are gradually better understood. They involve molecular signals from surrounding structures and the expression of a cascade of homeodomain transcription factors. Mutations of these transcription factors cause defects of embryologic development of the anterior pituitary responsible for isolated or multiple pituitary hormone deficiencies (respectively, IPHD and MPHD) in both rodents and humans. In this review we emphasize the description of human phenotypes associated with genetic alterations found in IPHD (e.g. isolated corticotroph deficiency and Tpit mutations) and MPHD (mutations of POU1F1, PROP1, Hesx1, Lhx3, Lhx4, Ptx2).

The de novo Q167K mutation in the POU1F1 gene leads to combined pituitary hormone deficiency in an Italian patient

The POU1F1 gene encodes a transcription factor that is important for the development and differentiation of the cells producing GH, prolactin, and TSH in the anterior pituitary gland. Patients with POU1F1 mutations show a combined pituitary hormone deficiency with low or absent levels of GH, prolactin, and TSH. Fourteen mutations have been reported in the POU1F1 gene up to now. These genetic lesions can be inherited either in an autosomal dominant or an autosomal recessive mode. We report on the first Italian patient, a girl, affected by combined pituitary hormone deficiency. The patient was found to be positive for congenital hypothyroidism (with low TSH levels) at neonatal screening. Substitutive therapy was started, but subsequent growth was very poor, although psychomotor development was substantially normal. Hospitalized at 10 mo she showed hypotonic crises, growth retardation, delayed bone age, and facial dysmorphism. In addition to congenital hypothyroidism, GH and prolactin deficiencies were found. Mutation DNA analysis of the patient's POU1F1 gene identified the novel Q167K amino acid change at the heterozygous level. The highly conserved Q167 residue is located in the POU-specific domain. No mutation was detected in the other allele. DNA analysis in the proband's parents did not identify this amino acid substitution, suggesting a de novo genetic lesion. From these data it can be hypothesized that the Q167K mutation has a dominant negative effect.

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.

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.

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.

LHX3 transcription factor mutations associated with combined pituitary hormone deficiency impair the activation of pituitary target genes

The Lhx3 LIM homeodomain transcription factor is critical for pituitary gland formation and specification of the anterior pituitary hormone-secreting cell types. Two mutations in LHX3, a missense mutation changing a tyrosine to a cysteine and an intragenic deletion that results in a truncated protein lacking the DNA-binding homeodomain, have been identified in humans. These mutations were identified in patients with retarded growth and combined pituitary hormone deficiency and also abnormal neck and cervical spine development. For both the LHX3a and LHX3b isoforms, we compared the ability of wild type and mutant LHX3 proteins to trans-activate pituitary genes, bind DNA recognition elements, and interact with partner proteins. The tyrosine missense mutation inhibits the ability of LHX3 to induce transcription from selected target genes but does not prevent DNA binding and interaction with partner proteins such as NLI and Pit-1. Mutant LHX3 proteins lacking a homeodomain do not bind DNA and do not induce transcription from pituitary genes. These studies demonstrate that mutations in the LHX3 isoforms impair their gene regulatory functions and support the hypothesis that defects in the LHX3 gene cause complex pituitary disease in humans.

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.

Genetic regulation of the embryology of the pituitary gland and somatotrophs

Extrinsic and intrinsic signaling gradients determine expression patterns of pituitary-specific factors in the developing anterior pituitary gland. The temporal and spatial relations of these developmental factors are required for the determination of each of the pituitary cell lineages. Rpx is required for early differentiation of the anterior pituitary. The determination of the somatotroph cell line is dependent on the transcription factors Lhx3, Prop-1, and Pit-1. Pit-1 also plays a role in the activation and regulation of the somatotroph gene product, GH. Additional factors such as CREB and the GHRH receptor, may be involved in somatotroph determination, while Zn-15 and Pitx2 may be involved in GH gene activation.

Genetic aspects of central hypothyroidism

Central hypothyroidism, characterized by insufficient TSH secretion in the presence of low levels of thyroid hormones, is a rare disorder. It has recently been found that, although mainly due to tumors or infiltrative diseases of the hypothalamo-pituitary area or to pituitary atrophy, central hypothyroidism may be caused by inactivating mutations in several of the genes that code for the various proteins involved in the regulation of the hypothalamo-pituitary-thyroid axis (HPTA). These experiments of nature allow us to better understand the pathophysiology but also the normal physiology of the HPTA. This review will analyze reports of mutations that affect the HPTA and result in either isolated central hypothyroidism or in the syndrome of combined pituitary hormone deficiency (CPHD). Mutations have been identified in the genes for the TRH receptor, the transcription factors Pit-1 and PROP1, and the TSH beta-subunit.

Combined pituitary hormone deficiency: role of Pit-1 and Prop-1

During fetal development of the anterior pituitary gland, a number of sequential processes occur that affect cell differentiation and proliferation. Molecular analyses have revealed several steps that are required for pituitary cell line specification and have identified specific factors that control these steps. The gene encoding the pituitary transcription factor 1 (Pit-1) is expressed during differentiation steps that take place quite late in the development of the anterior pituitary gland. Clinically, patients with mutations of the PIT1 gene are characterized by severe deficiencies in growth hormone (GH) and prolactin (PRL), and often develop secondary hypothyroidism. A second pituitary transcription factor is known as Prophet of Pit-1 (Prop-1), and a mutation of the Prop1 gene has been detected in Ames dwarf mice. Several Prop1 mutations have been identified that structurally affect the 'paired-like' DNA-binding domain of the Prop-1 protein molecule. Patients with PROP1 mutations show combined pituitary hormone deficiency. These patients exhibit secondary hypogonadism in addition to the deficiencies of GH, PRL and thyroid-stimulating hormone (TSH) also seen in patients with PIT1 mutations. Although all are in the subnormal range, the levels of GH, PRL and TSH in patients with PROP1 mutations are, on average, slightly higher than in patients with PIT1 mutations. Some degree of hypocortisolism may necessitate cortisol substitution in patients with PROP1 mutations.

Heritable disorders of pituitary development

Basic and translational research achievements over the past 2 decades have disclosed the molecular mechanisms underlying several genetic forms of hypopituitarism. Disorders that are limited to the hypothalamic, pituitary, GH axis are caused by mutations in individual components of that axis. Disorders involving GH and one or more additional pituitary hormones are caused by mutations in the homeodomain transcription factors that direct embryological development of the anterior pituitary gland. Pit-1 has a POU-specific and a POU-homeo DNA-binding domain. The phenotype produced by mutations in the PIT1 gene involves deficiencies of GH, PRL, and TSH. Pituitary glands are either small or normally sized. The PROP1 gene encodes a transcription factor with a single paired-like DNA-binding domain. Persons with inactivating mutations in PROP1 have deficiencies of LH and FSH, as well as GH, PRL, and TSH. Their pituitary glands may be small, normally sized, or extremely large and show suprasellar extension. Pituitary degeneration may produce acquired deficiency of ACTH. Expression of the HESX1 gene precedes expression of PROP1 and PIT1, and it is much more widespread. The protein has a paired-like domain, and it competes with the product of PROP1 for DNA-binding. Homozygosity for inactivating mutations of HESX1 produces a complex phenotype that resembles septo-optic dysplasia. Much more needs to be learned about the role of HESX1 mutations in other forms of hypopituitarism.

Transcription Factors and Hypopituitarism

Several homeodomain factors are found in the developing anterior pituitary lobe. The production of these developmental transcription factors has distinct temporal and spatial patterns. By interacting with each other, as well as with other extrinsic and intrinsic signals, they control cell determination and specification. Here, we discuss transcription factors that have been shown to have an in vivo role in pituitary cell-type specification.

Defective retinoic acid regulation of the Pit-1 gene enhancer: a novel mechanism of combined pituitary hormone deficiency

Pit-1 is a pituitary-specific transcription factor responsible for pituitary development and hormone expression in mammals. Pit-1 contains two protein domains, termed POU-specific and POU-homeo, which are both necessary for DNA binding and activation of the GH and PRL genes and regulation of the PRL, TSH-beta subunit (TSH-beta), and Pit-1 genes. Pit-1 is also necessary for retinoic acid induction of its own gene during development through a Pit-1-dependent enhancer. Combined pituitary hormone deficiency is caused by defective transactivation of target genes in the anterior pituitary. In the present report, we provide in vivo evidence that retinoic acid induction of the Pit-1 gene can be impaired by a Pit-1 gene mutation, suggesting a new molecular mechanism for combined pituitary hormone deficiency in man.

Clinical and molecular characterization of a Brazilian patient with Pit-1 deficiency

We studied a 14 year-old girl with extreme short stature (-9.5 SDS), normal psychomotor development and signs of progressive hypothyroidism. Basal IGF-I and T4 were low. Serum GH was low after insulin-induced hypoglycemia and GH-releasing hormone administration. Both TSH and prolactin were low and did not rise after TRH administration. Gonadotropins were normal and cortisol levels were elevated. In contrast, DHEA-S levels were low and she did not develop pubic hair until 26 years of age, compatible with deficiency of a putative pituitary adrenal androgen stimulating hormone. Pituitary size was reduced on magnetic resonance imaging. Sequencing of the Pit-1 gene revealed a heterozygous C to T transition in codon 271 resulting in substitution of tryptophane for a highly conserved arginine. Her parents were homozygous normal for this locus indicating a de novo mutation with dominant expression. Genetic and phenotypic heterogeneity of patients with Pit-1 gene mutations, particularly the R271W mutation, may reveal further information about the nature of genetic silencing, imprinting, and epigenetic inheritance. The relationship of Pit-1 deficiency to abnormal adrenal secretion remains to be elucidated.

Rarity of PIT1 involvement in children from Russia with combined pituitary hormone deficiency

To ascertain the molecular background of combined pituitary hormone deficiency, screening for mutations in the pituitary-specific transcription factor (Pit-1/GHF-1) gene (PIT1) was performed on a cohort of 15 children from Russia with combined growth hormone (GH)/prolactin (Prl)/thyroid-stimulating hormone (TSH) deficiency. The group of patients, suspected of PIT1 mutations, consisted of four familial cases (seven patients) and eight sporadic cases. All had complete GH deficiency and complete or partial Prl and TSH deficiency. Direct sequencing of all six exons of PIT1 and its promoter region showed a C to T transition mutation at codon 14 of exon 1 in a 3 8/12-year-old girl. This novel PIT1 mutation results in a proline to leucine substitution (P14L). The patient was heterozygous for mutant and normal alleles. The heterozygous P14L mutation was also present in her mother as well as in her maternal aunt and grandmother, all of whom were phenotypically normal. There was no mutation in the father's DNA, suggesting the need for reevaluation of genomic imprinting. In other children of our series, no mutation in PIT1 or in its promotor region was identified. This is the first report on the analysis of PIT1 and its promoter region in Russian children with GH/Prl/TSH deficiency. However, as the involvement of PIT1 mutation is rare in Russia, the other negative cases need to be analyzed for another candidate gene responsible for combined GH/Pr/TSH deficiency.

Pro239Ser: a novel recessive mutation of the Pit-1 gene in seven Middle Eastern children with growth hormone, prolactin, and thyrotropin deficiency

Pit-1, a member of the POU-homeo domain protein family, is one of the transcription factors responsible for anterior pituitary development and pituitary-specific gene expression. Here, we describe seven children with GH, PRL, and TSH deficiency from three, reportedly unrelated, Middle Eastern families, harboring a newly recognized Pro- > Ser recessive mutation in codon 239 of the Pit-1 gene. The mutated residue is located at the beginning of the second alpha-helix of the POU-homeodomain and is strictly conserved among all POU proteins. The Pro239Ser mutant binds DNA normally but is unable to stimulate transcription.

Severe congenital hypopituitarism with low prolactin levels and age-dependent anterior pituitary hypoplasia: a clue to a PIT-1 mutation

A 20-month-old boy presented with severe congenital growth hormone, thyrotropin, and prolactin deficiencies resulting from a de novo mutation of the PIT-1 gene. This form of congenital hypopituitarism should be suspected if pituitary anatomy is normal, especially if prolactin levels are low and, in boys, if the external genitalia are normal. Pituitary atrophy appears to be an age-dependent phenomenon in this condition.

Construction of a 3-Mb contig and partial transcript map of the central region of mouse chromosome 11

We report the establishment of a high-resolution genetic map, a physical map, and a partial transcript map of the Ames dwarf critical region on mouse chromosome 11. A contig of 24 YACs and 13 P1 clones has been assembled and spans approximately 3 Mb from Flt4 to Tcf7. A library of approximately 1000 putative transcript clones from the region was prepared using exon amplification and pituitary cDNA selection. Ten novel transcripts were partially characterized, including a member of the olfactory receptor family, an alpha-tubulin-related sequence, and a novel member of the cdc2/CDC28-like kinase family, Clk4. The location of Prop1, the gene responsible for Ames dwarfism, has been localized within the contig. This contig spans a region of mouse chromosome 11 that exhibits linkage conservation with human chromosome 5q23-q35. The strength of the genetic map and genomic resources for this region suggest that comparative DNA sequencing of this region could reveal the genes responsible for other mouse mutants and human genetic diseases.

Structure of Pit-1 POU domain bound to DNA as a dimer: unexpected arrangement and flexibility

Pit-1, a member of the POU domain family of transcription factors, characterized by a bipartite DNA-binding domain, serves critical developmental functions based on binding to diverse DNA elements in its target genes. Here we report a high resolution X-ray analysis of the Pit-1 POU domain bound to a DNA element as a homodimer. This analysis reveals that Pit-1 subdomains bind to perpendicular faces of the DNA, rather than opposite faces of the DNA as in Oct-1. This is accomplished by different spacing and orientation of the POU-specific domain. Contrary to previous predictions, the dimerization interface involves the carboxyl terminus of the DNA recognition helix of the homeodomain, which in an extended conformation interacts with specific residues at the amino terminus of helix alpha1 and in the loop between helices alpha3 and alpha4 of the POU-specific domain of the symmetry related monomer. These features suggest the molecular basis of disease-causing mutations in Pit-1 and provide potential basis for the flexible allostery between protein domains and DNA sites in the activation of target genes.