A model for the development of the hypothalamic-pituitary axis: transcribing the hypophysis

Missing pieces of the pituitary puzzle: participation of extra-adenohypophyseal placode-lineage cells in the adult pituitary gland

The pituitary gland is a major endocrine tissue composing of two distinct entities, the adenohypophysis (anterior pituitary, cranial placode origin) and the neurohypophysis (posterior pituitary, neural ectoderm origin), and plays important roles in maintaining vital homeostasis. This tissue is maintained by a slow, consistent cell-renewal system of adult stem/progenitor cells. Recent accumulating evidence shows that neural crest-, head mesenchyme-, and endoderm lineage cells invade during pituitary development and contribute to the maintenance of the adult pituitary gland. Based on these novel observations, this article discusses whether these lineage cells are involved in pituitary organogenesis, maintenance, regeneration, dysplasia, or tumors.

POU6F2 mutation in humans with pubertal failure alters GnRH transcript expression

Idiopathic hypogonadotropic hypogonadism (IHH) is characterized by the absence of pubertal development and subsequent impaired fertility often due to gonadotropin-releasing hormone (GnRH) deficits. Exome sequencing of two independent cohorts of IHH patients identified 12 rare missense variants in POU6F2 in 15 patients. POU6F2 encodes two distinct isoforms. In the adult mouse, expression of both isoform1 and isoform2 was detected in the brain, pituitary, and gonads. However, only isoform1 was detected in mouse primary GnRH cells and three immortalized GnRH cell lines, two mouse and one human. To date, the function of isoform2 has been verified as a transcription factor, while the function of isoform1 has been unknown. In the present report, bioinformatics and cell assays on a human-derived GnRH cell line reveal a novel function for isoform1, demonstrating it can act as a transcriptional regulator, decreasing GNRH1 expression. In addition, the impact of the two most prevalent POU6F2 variants, identified in five IHH patients, that were located at/or close to the DNA-binding domain was examined. Notably, one of these mutations prevented the repression of GnRH transcripts by isoform1. Normally, GnRH transcription increases as GnRH cells mature as they near migrate into the brain. Augmentation earlier during development can disrupt normal GnRH cell migration, consistent with some POU6F2 variants contributing to the IHH pathogenesis.

Prevalence of pituitary dysfunction after aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis

BACKGROUND

Pituitary dysfunction (PD) is a common complication after aneurysmal subarachnoid hemorrhage (aSAH). The prevalence of PD varies widely at a global level and no recent meta-analysis is available. Therefore, the aim of our systematic review and meta-analysis was to summarize the updated estimates of worldwide prevalence of PD after aSAH.

METHODS

Scopus, Embase, Web of Science, and PubMed databases were used to comprehensively search the appropriate literature and a random-effects meta-analysis on the results of the available studies was performed. The heterogeneity in the prevalence estimates was evaluated by subgroup analysis in terms of types of PD, and acute and chronic phases of aSAH. The onset of PD within 6 months after aSAH was considered as acute, while that after 6 months was considered as chronic.

RESULTS

Twenty-seven studies with 1848 patients were included in this analysis. The pooled prevalence of PD in the acute phase was 49.6% (95% CI, 32.4-66.8%), and 30.4% (95% CI, 21.4-39.4%) in the chronic phase. Among the hormonal deficiencies, growth hormone dysfunction was the most prevalent in the acute phase, being 36.0% (95% CI, 21.0-51.0%), while hypoadrenalism was the most prevalent in the chronic phase, being 21.0% (95% CI, 12.0-29.0%). Among the six World Health Organization regions, the South-East Asia Region has the highest prevalence of PD in the acute phase (81.0%, 95%CI, 77.0-86.0%, P < 0.001), while the European Region had the highest prevalence of PD in the chronic phase (33.0%, 95%CI, 24.0-43.0%, P < 0.001). Moreover, single pituitary hormonal dysfunction occurred more frequently than the multiple one, regardless of acute or chronic phase.

CONCLUSIONS

Almost half (49.6%) of the included patients with aSAH developed PD complication in the acute phase, while 30.4% of the patients developed them in the chronic phase. Although prevalence varies globally, the high healthcare burden, morbidity and mortality require greater awareness among clinicians.

New insights into the role and origin of pituitary S100β-positive cells

In the anterior pituitary, S100β protein (S100β) has been assumed to be a marker of folliculo-stellate cells, which are one of the non-hormone-producing cells existing in the parenchyma of the adult anterior lobe and are composed of subpopulations with various functions. However, recent accumulating studies on S100β-positive cells, including non-folliculo-stellate cells lining the marginal cell layer (MCL), have shown the novel aspect that most S100β-positive cells in the MCL and parenchyma of the adult anterior lobe are positive for sex determining region Y-box 2 (SOX2), a marker of pituitary stem/progenitor cells. From the viewpoint of SOX2-positive cells, the majority of these cells in the MCL and in the parenchyma are positive for S100β, suggesting that S100β plays a role in the large population of stem/progenitor cells in the anterior lobe of the adult pituitary. Reportedly, S100β/SOX2-double positive cells are able to differentiate into hormone-producing cells and various types of non-hormone-producing cells. Intriguingly, it has been demonstrated that extra-pituitary lineage cells invade the pituitary gland during prenatal pituitary organogenesis. Among them, two S100β-positive populations have been identified: one is SOX2-positive population which invades at the late embryonic period through the pituitary stalk and another is a SOX2-negative population that invades at the middle embryonic period through Atwell's recess. These two populations are likely the substantive origin of S100β-positive cells in the postnatal anterior pituitary, while S100β-positive cells emerging from oral ectoderm-derived cells remain unclear.

Pituitary Remodeling Throughout Life: Are Resident Stem Cells Involved?

The pituitary gland has the primordial ability to dynamically adapt its cell composition to changing hormonal needs of the organism throughout life. During the first weeks after birth, an impressive growth and maturation phase is occurring in the gland during which the distinct hormonal cell populations expand. During pubertal growth and development, growth hormone (GH) levels need to peak which requires an adaptive enterprise in the GH-producing somatotrope population. At aging, pituitary function wanes which is associated with organismal decay including the somatopause in which GH levels drop. In addition to these key time points of life, the pituitary's endocrine cell landscape plastically adapts during specific (patho-)physiological conditions such as lactation (need for PRL) and stress (engagement of ACTH). Particular resilience is witnessed after physical injury in the (murine) gland, culminating in regeneration of destroyed cell populations. In many other tissues, adaptive and regenerative processes involve the local stem cells. Over the last 15 years, evidence has accumulated that the pituitary gland houses a resident stem cell compartment. Recent studies propose their involvement in at least some of the cell remodeling processes that occur in the postnatal pituitary but support is still fragmentary and not unequivocal. Many questions remain unsolved such as whether the stem cells are key players in the vivid neonatal growth phase and whether the decline in pituitary function at old age is associated with decreased stem cell fitness. Furthermore, the underlying molecular mechanisms of pituitary plasticity, in particular the stem cell-linked ones, are still largely unknown. Pituitary research heavily relies on transgenic in vivo mouse models. While having proven their value, answers to pituitary stem cell-focused questions may more diligently come from a novel powerful in vitro research model, termed organoids, which grow from pituitary stem cells and recapitulate stem cell phenotype and activation status. In this review, we describe pituitary plasticity conditions and summarize what is known on the involvement and phenotype of pituitary stem cells during these pituitary remodeling events.

Persisting Embryonal Infundibular Recess (PEIR): Two Case Reports and Systematic Literature Review

CONTEXT

The persisting embryonal infundibular recess (PEIR) is a rare anomaly of the floor of the third ventricle with a debated pathogenesis. It can be a cause of misdiagnosis in the case of cystic lesions of the sellar and suprasellar area.

OBJECTIVE

To describe two recently evaluated cases and provide a systematic literature review.

EVIDENCE ACQUISITION AND CASE DESCRIPTIONS

PEIR has been previously reported in six adult patients. Because in some cases it was associated with hydrocephalus and/or empty sella, a possible role of altered intracranial pressure in PEIR formation has been postulated. We evaluated two female patients, aged 34 and 50 years, referred to the Pituitary Surgery Clinic of the University of Brescia with the diagnosis of a sellar cyst and craniopharyngioma, respectively. Endocrine screening and visual field testing were normal. No signs of hydrocephalus or empty sella, as well as other indirect signs of intracranial hypertension, were visible on MRI scans. After a multidisciplinary reevaluation, diagnosis of PEIR was made in both cases. Both patients are followed but have not developed any disturbance related to the PEIR in the following 18 months.

CONCLUSIONS

PEIR is a rare condition, probably unrecognized and the result of dysembriogenesis, which should be included in the differential diagnosis of cystic sellar lesions. Imaging features (funnel pituitary stalk and cyst in the sella) appear pathognomonic. A normal endocrine evaluation might help in the diagnosis and warrants conservative treatment.

Prolactin regulates liver growth during postnatal development in mice

The liver grows during the early postnatal period first at slower and then at faster rates than the body to achieve the adult liver-to-body weight ratio (LBW), a constant reflecting liver health. The hormone prolactin (PRL) stimulates adult liver growth and regeneration, and its levels are high in the circulation of newborn infants, but whether PRL plays a role in neonatal liver growth is unknown. Here, we show that the liver produces PRL and upregulates the PRL receptor in mice during the first 2 wk after birth, when liver growth lags behind body growth. At postnatal week 4, the production of PRL by the liver ceases coinciding with the elevation of circulating PRL and the faster liver growth that catches up with body growth. PRL receptor null mice ( Prlr−/−) show a significant decrease in the LBW at 1, 4, 6, and 10 postnatal weeks and reduced liver expression of proliferation [cyclin D1 ( Ccnd1)] and angiogenesis [platelet/endothelial cell adhesion molecule 1 ( Pecam1)] markers relative to Prlr+/+ mice. However, the LBW increases in Prlr−/− mice at postnatal week 2 concurring with the enhanced liver expression of Igf-1 and the liver upregulation and downregulation of suppressor of cytokine signaling 2 ( Socs2) and Socs3, respectively. These findings indicate that PRL acts locally and systemically to restrict and stimulate postnatal liver growth. PRL inhibits liver and body growth by attenuating growth hormone-induced Igf-1 liver expression via Socs2 and Socs3-related mechanisms.

Foxl2 and Its Relatives Are Evolutionary Conserved Players in Gonadal Sex Differentiation

Foxl2 is a member of the large family of Forkhead Box (Fox) domain transcription factors. It emerged during the last 15 years as a key player in ovarian differentiation and oogenesis in vertebrates and especially mammals. This review focuses on Foxl2 genes in light of recent findings on their evolution, expression, and implication in sex differentiation in animals in general. Homologs of Foxl2 and its paralog Foxl3 are found in all metazoans, but their gene evolution is complex, with multiple gains and losses following successive whole genome duplication events in vertebrates. This review aims to decipher the evolutionary forces that drove Foxl2/3 gene specialization through sub- and neo-functionalization during evolution. Expression data in metazoans suggests that Foxl2/3 progressively acquired a role in both somatic and germ cell gonad differentiation and that a certain degree of sub-functionalization occurred after its duplication in vertebrates. This generated a scenario where Foxl2 is predominantly expressed in ovarian somatic cells and Foxl3 in male germ cells. To support this hypothesis, we provide original results showing that in the pea aphid (insects) foxl2/3 is predominantly expressed in sexual females and showing that in bovine ovaries FOXL2 is specifically expressed in granulosa cells. Overall, current results suggest that Foxl2 and Foxl3 are evolutionarily conserved players involved in somatic and germinal differentiation of gonadal sex.

Crossreaction with an Anti-Bax Antibody Reveals Novel Multi-endocrine Cellular Antigen

We found a novel protein that has crossreactivity with a polyclonal anti-Bax antibody (SCBAX antibody). The protein was localized exclusively in the endocrine cells of hypothalamus, pituitary gland, and pancreatic islets. Immunohistochemical (IHC) double labeling revealed that the cells showing crossreactivity with this antibody corresponded precisely to oxytocin neurons and ACTH, α-MSH, and glucagon cells in rat and gerbil. By immunoelectron microscopy, the protein was localized predominantly in and just around the secretory granules in the cytoplasm but not in the mitochondria. Double-labeling IHC with the anti-Bax SCBAX antibody and two anti-Bax monoclonal antibodies (MAbs) showed that cells stained with the anti-Bax SCBAX antibody were not stained with anti-Bax MAbs except for very few cells (probably apoptotic cells). Western blotting analysis revealed that the molecular mass of the protein was ∼55 kD, which differs from that of Bax protein (21 kD). These findings indicate that the anti-Bax SCBAX antibody recognizes not only proapoptotic Bax protein (a 21-kD mitochondrial protein) but also an unknown substance present in one endocrine cell group in each endocrine organ. Therefore, the protein is designated as multi-endocrine cellular antigen (MECA). MECA is probably a 55-kD protein secreted from the particular differentiated cell groups of endocrine tissues. (J Histochem Cytochem 52:805–812, 2004)

Search for regulatory factors of the pituitary-specific transcription factor PROP1 gene

Pituitary-specific transcription factor PROP1, a factor important for pituitary organogenesis, appears on rat embryonic day 11.5 (E11.5) in SOX2-expressing stem/progenitor cells and always coexists with SOX2 throughout life. PROP1-positive cells at one point occupy all cells in Rathke’s pouch, followed by a rapid decrease in their number. Their regulatory factors, except for RBP-J, have not yet been clarified. This study aimed to use the 3 kb upstream region and 1st intron of mouse prop1 to pinpoint a group of factors selected on the basis of expression in the early pituitary gland for expression of Prop1. Reporter assays for SOX2 and RBP-J showed that the stem/progenitor marker SOX2 has cell type-dependent inhibitory and activating functions through the proximal and distal upstream regions of Prop1, respectively, while RBP-J had small regulatory activity in some cell lines. Reporter assays for another 39 factors using the 3 kb upstream regions in CHO cells ultimately revealed that 8 factors, MSX2, PAX6, PIT1, PITX1, PITX2, RPF1, SOX8 and SOX11, but not RBP-J, regulate Prop1 expression. Furthermore, a synergy effect with SOX2 was observed for an additional 10 factors, FOXJ1, HES1, HEY1, HEY2, KLF6, MSX1, RUNX1, TEAD2, YBX2 and ZFP36Ll, which did not show substantial independent action. Thus, we demonstrated 19 candidates, including SOX2, to be regulatory factors of Prop1 expression.

Pituitary dysfunction after aneurysmal subarachnoid haemorrhage: course and clinical predictors—the HIPS study

OBJECTIVE

We describe the occurrence and course of anterior pituitary dysfunction (PD) after aneurysmal subarachnoid haemorrhage (SAH), and identify clinical determinants for PD in patients with recent SAH.

METHODS

We prospectively collected demographic and clinical parameters of consecutive survivors of SAH and measured fasting state endocrine function at baseline, 6 and 14 months. We included dynamic tests for growth-hormone function. We used logistic regression analysis to compare demographic and clinical characteristics of patients with SAH with and without PD.

RESULTS

84 patients with a mean age of 55.8 (±11.9) were included. Thirty-three patients (39%) had PD in one or more axes at baseline, 22 (26%) after 6 months and 6 (7%) after 14 months. Gonadotropin deficiency in 29 (34%) patients and growth hormone deficiency (GHD) in 26 (31%) patients were the most common deficiencies. PD persisted until 14 months in 6 (8%) patients: GHD in 5 (6%) patients and gonadotropin deficiency in 4 (5%). Occurrence of a SAH-related complication was associated with PD at baseline (OR 2.6, CI 2.2 to 3.0). Hydrocephalus was an independent predictor of PD 6 months after SAH (OR 3.3 CI 2.7 to 3.8). PD was associated with a lower score on health-related quality of life at baseline (p=0.06), but not at 6 and 14 months.

CONCLUSIONS

Almost 40% of SAH survivors have PD. In a small but substantial proportion of patients GHD or gonadotropin deficiency persists over time. Hydrocephalus is independently associated with PD 6 months after SAH.

TRIAL REGISTRATION NUMBER

NTR 2085.

Characterization of proopiomelanocortin in the snakeskin gourami (Trichopodus pectoralis) and its expression in relation to food intake

Proopiomelanocortin (POMC) is the precursor of several hormones involved in physiological systems including feed intake. The snakeskin gourami (Trichopodus pectoralis) POMC complementary DNA (TpPOMC) was cloned and characterized. Phylogenetic analysis showed that TpPOMC was clustered in a major POMC lineage in fish. Analysis of the Ka to Ks ratios for the entire POMC sequence and for each hormonal segment suggested that different POMC-derived peptide segments were subject to different evolutionary pressures. High expression level of TpPOMC was observed in all brain regions, with the highest levels in the diencephalon and pituitary gland. In situ hybridization also revealed that TpPOMC-expressing cells were distributed in discrete brain regions. The transcription level of TpPOMC was also found at moderate levels in several peripheral tissues, including gills, liver, head kidney, trunk kidney, stomach, intestine, spleen, ovary and testis, and at a low level in muscle. The expression level of TpPOMC was evaluated in each brain region (telencephalon, mesencephalon, metencephalon, and diencephalon together with the pituitary gland) at 1 h before the first and the last meals of the day and compared with expression levels at a time interval between the first and the last meals of the day. Low expression levels of TpPOMC were found at 1 h before the last meal of the day (P < 0.05). These finding suggest that decreased POMC expression level may lead to reduced melanocyte-stimulating hormones, which may in part be responsible for stimulating food intake. The effect of short-term fasting (24 h) on TpPOMC expression level in each brain region was also investigated. In telencephalon and diencephalon together with the pituitary gland, TpPOMC messenger RNA reached a nadir at 12 h of fasting, whereas TpPOMC transcript showed a nadir at 6 h of fasting in metencephalon and mesencephalon. A peak of TpPOMC level was observed at 18 h of fasting in metencephalon and diencephalon together with the pituitary gland. These findings suggest that TpPOMC expression is affected by nutritional status.

Molecular cloning of rat and porcine retina-derived POU domain factor 1 (POU6F2) from a pituitary cDNA library

Homeobox transcription factors are known to play crucial roles in the anterior lobe of the pituitary gland. During molecular cloning with the Yeast One-Hybrid System using a 5'-upstream region of the porcine Fshβ as a bait sequence, we have cloned a cDNA encoding a partial sequence of the retina-derived POU domain factor 1 (RPF1) from the porcine pituitary cDNA library and confirmed its specific binding to the bait sequence. In situ hybridization was performed to examine localization of Rpf1 and showed that this gene is expressed in the stem/progenitor cells of the rat pituitary primordium as well as the diencephalon and retina. In addition, real-time PCR demonstrated that Rpf1 transcripts are abundant in early embryonic periods but that this is followed by a decrease during pituitary development, indicating that this factor plays a role in differentiating cells of the pituitary. The transcriptional activity of RPF1 for genes of Prop1, Prrx1 and Prrx2, which were characterized as genes participating in the pituitary stem/progenitor cells by our group, was then examined with full-length cDNA obtained from the rat pituitary. RPF1 showed regulatory activity for Prop1 and Prrx2, but not for Prrx1. These results indicate the involvement of this retina-derived factor in pituitary development.

BMP action in the pituitary: its possible role in modulating somatostatin sensitivity in pituitary tumor cells

The existence of a functional bone morphogenetic protein (BMP) system in the pituitary has been recognized. Recent studies have provided evidence that BMPs elicit differential actions in the regulation of prolactin (PRL) and adrenocorticotropin (ACTH) release in lactotropinoma and corticotropinoma cells, respectively. BMPs play a key role in the modulation of somatostatin receptor (SSTR) sensitivity of lactosomatotrope cells in an autocrine/paracrine manner. In addition, SSTR action enhances BMP responsiveness in corticotrope cells. The functional link between BMP receptor signaling and SSTR actions may be crucial for individual tolerance to somatostatin analogs for controlling PRL and ACTH production. Adjustment of the endogenous SSTR sensitivity may be an effective strategy to inhibit the growth activity and hormonal productivity of intractable pituitary tumors.

Molecular cloning of LIM homeodomain transcription factor Lhx2 as a transcription factor of porcine follicle-stimulating hormone beta subunit (FSHβ) gene

We cloned the LIM-homeodomain protein LHX2 as a transcription factor for the porcine follicle-stimulating hormone β subunit gene (Fshβ) by the Yeast One-Hybrid Cloning System using the upstream region of -852/-746 bases (b) from the transcription start site, called Fd2, as a bait sequence. The reporter assay in LβT2 and CHO cells revealed the presence of an LHX2-responsive region other than Fd2. A potential LHX2 binding sequence was confirmed as AATTAAT containing a consensus homeodomain binding core sequence AATT by Systematic Evolution of Ligands by Exponential Enrichment analysis. DNase I footprinting demonstrated three AATTAAT sequences located at regions -835/-829, -818/-812 and -806/-800 b in the Fd2 region and 12 binding sites in the distal and proximal regions mostly containing an AATT-core sequence. RT-PCR analysis of Lhx2 expression during porcine fetal and postnatal pituitary development showed a gradual increase from fetal day (f) 40 to postnatal day (p) 8 followed by a slight decrease to p230, suggesting that LHX2 may play its role largely in the late fetal and postnatal periods. The analyses of Lhx2 expression in pituitary tumor-derived cell lines showed their expressions in cell lines including αT31, LβT2 and others. Since LHX2 was previously identified as a transcription factor for Cga and the in vitro experiments in the present study suggested that LHX2 regulated the expression of Fshβ, it is possible that LHX2 controls the synthesis of FSH at the transcription level.

Activities of bone morphogenetic proteins in prolactin regulation by somatostatin analogs in rat pituitary GH3 cells

Involvement of the pituitary BMP system in the modulation of prolactin (PRL) secretion regulated by somatostatin analogs, including octreotide (OCT) and pasireotide (SOM230), and a dopamine agonist, bromocriptine (BRC), was examined in GH3 cells. GH3 cells are rat pituitary somato-lactotrope tumor cells that express somatostatin receptors (SSTRs) and BMP system molecules including BMP-4 and -6. Treatment with BMP-4 and -6 increased PRL and cAMP secretion by GH3 cells. The BMP-4 effects were neutralized by adding a BMP-binding protein Noggin. These findings suggest the activity of endogenous BMPs in augmenting PRL secretion by GH3 cells. BRC and SOM230 reduced PRL secretion, but OCT failed to reduce the PRL level. In GH3 cells activated by forskolin, BRC suppressed forskolin-induced PRL secretion with reduction in cAMP levels. OCT did not affect forskolin-induced PRL level, while SOM230 reduced PRL secretion and PRL mRNA expression induced by forskolin. BMP-4 treatment enhanced the reducing effect of SOM230 on forskolin-induced PRL level while BMP-4 did not affect the effects of OCT or BRC. Noggin treatment had no significant effect on the BRC actions reducing PRL levels by GH3 cells. However, in the presence of Noggin, OCT elicited an inhibitory effect on forskolin-induced PRL secretion and PRL mRNA expression, whereas the SOM230 effect on PRL reduction was in turn impaired. It was further found that BMP-4 and -6 suppressed SSTR-2 but increased SSTR-5 mRNA expression of GH3 cells. These findings indicate that Noggin rescues SSTR-2 but downregulates SSTR-5 by neutralizing endogenous BMP actions, leading to an increase in OCT sensitivity and a decrease in SOM230 sensitivity of GH3 cells. In addition, BMP signaling was facilitated in GH3 cells treated with forskolin. Collectively, these findings suggest that BMPs elicit differential actions in the regulation of PRL release dependent on cellular cAMP-PKA activity. BMPs may play a key role in the modulation of SSTR sensitivity of somato-lactotrope cells in an autocrine/paracrine manner.

Effects of bone morphogenetic protein (BMP) on adrenocorticotropin production by pituitary corticotrope cells: involvement of up-regulation of BMP receptor signaling by somatostatin analogs

The mechanism by which somatostatin analogs suppress ACTH production by corticotropinomas has yet to be fully elucidated. We here studied the effects of somatostatin analogs on ACTH secretion using mouse corticotrope AtT20 cells focusing on the biological activity of bone morphogenetic proteins (BMPs). BMP ligands, receptors and Smads, and somatostatin receptors (SSTRs)-2, -3, and -5 were expressed in AtT20 cells. BMP-2, -4, -6, and -7 decreased basal ACTH production with BMP-4 effects being the most prominent. BMP-4 also inhibited CRH-induced ACTH production and proopiomelanocortin (POMC) transcription. However, the decrease in CRH-induced cAMP accumulation caused by BMP-4 was not sufficient to completely account for BMP-4 actions, indicating that ACTH suppression by BMPs was not directly linked to cAMP inhibition. CRH-activated ERK1/ERK2, p38-MAPK, stress-activated protein kinase/c-Jun NH(2)-terminal kinase, protein kinase C, and Akt pathways and CRH-induced ACTH synthesis was significantly decreased in the presence of U0126 or SB203580. Because BMPs attenuated CRH-induced ERK and p38 phosphorylation, it was suggested that BMP-4 suppresses ACTH production by inhibiting CRH-induced ERK and p38 phosphorylation. Somatostatin analogs octreotide and pasireotide (SOM230) significantly suppressed CRH-induced ACTH and cAMP production in AtT20 cells and reduced ERK and p38 phosphorylation. Notably, CRH-induced ACTH production was enhanced in the presence of noggin, a BMP-binding protein. The inhibitory effects of octreotide and SOM230 on CRH-induced ACTH production were also attenuated by noggin, implying that the endogenous BMP system plays a key role in inhibiting CRH-induced ACTH production by AtT20 cells. The findings that OCT and SOM230 up-regulated BMP-Smad1/Smad5/Smad8 signaling and ALK-3 and BMPRII and down-regulated inhibitory Smad6/7 establish that the activation of endogenous BMP system is functionally involved in the mechanism by which somatostatin analogs suppress CRH-induced ACTH production.

Making senses development of vertebrate cranial placodes

Cranial placodes (which include the adenohypophyseal, olfactory, lens, otic, lateral line, profundal/trigeminal, and epibranchial placodes) give rise to many sense organs and ganglia of the vertebrate head. Recent evidence suggests that all cranial placodes may be developmentally related structures, which originate from a common panplacodal primordium at neural plate stages and use similar regulatory mechanisms to control developmental processes shared between different placodes such as neurogenesis and morphogenetic movements. After providing a brief overview of placodal diversity, the present review summarizes current evidence for the existence of a panplacodal primordium and discusses the central role of transcription factors Six1 and Eya1 in the regulation of processes shared between different placodes. Upstream signaling events and transcription factors involved in early embryonic induction and specification of the panplacodal primordium are discussed next. I then review how individual placodes arise from the panplacodal primordium and present a model of multistep placode induction. Finally, I briefly summarize recent advances concerning how placodal neurons and sensory cells are specified, and how morphogenesis of placodes (including delamination and migration of placode-derived cells and invagination) is controlled.

Senescence mediates pituitary hypoplasia and restrains pituitary tumor growth

Understanding factors subserving pituitary cell proliferation enables understanding mechanisms underlying uniquely benign pituitary tumors. Pituitary tumor-transforming gene (Pttg) deletion results in pituitary hypoplasia, low pituitary cell proliferation rates, and rescue of pituitary tumor development in Rb(+/-) mice. Pttg(-/-) pituitary glands exhibit ARF/p53/p21-dependent senescence pathway activation evidenced by up-regulated p19, cyclin D1, and Bcl-2 protein levels and p53 stabilization. High pituitary p21 levels in the absence of PTTG were associated with suppressed cyclin-dependent kinase 2 activity, Rb phosphorylation, and cyclin A expression, all required for cell cycle progression. Although senescence-associated beta-galactosidase was enhanced in Pttg-deficient pituitary glands, telomere lengths were increased. DNA damage signaling pathways were activated and aneuploidy was evident in the Pttg-deficient pituitary, triggering senescence-associated genes. To confirm the p21 dependency of decreased proliferation and senescence in the Pttg-null pituitary, mouse embryonic fibroblast (MEF) colony formation was tested in wild-type, Pttg(-/-), Rb(+/-), Rb(+/-)Pttg(-/-), and Rb(+/-)Pttg(-/-)p21(-/-) cells. Rb(+/-)Pttg(-/-) MEFs, unlike Rb(+/-) cells, failed to produce colonies and exhibited high levels of senescence. p21 deletion from Rb(+/-)Pttg(-/-) MEFs enhanced anchorage-independent cell growth, accompanied by a marked decrease in senescence. As cell proliferation assessed by bromodeoxyuridine incorporation was higher in Rb(+/-)Pttg(-/-)p21(-/-) relative to Rb(+/-)Pttg(-/-) pituitary glands, p21-dependent senescence provoked by Pttg deletion may underlie pituitary hypoplasia and decreased tumor development in Rb(+/-)Pttg(-/-) mice.

Gene structure and seasonal expression of carp fish prolactin short receptor isoforms

The complex adaptive mechanisms that eurythermal fish have evolved in response to the seasonal changes of the environment include the transduction of the physical parameter variations into neuroendocrine signals. Studies in carp (Cyprinus carpio) have indicated that prolactin (PRL) and growth hormone (GH) expression is associated with acclimatization, suggesting that the pituitary gland is a relevant physiological node in this adaptive process. Also, the distinctive pattern of expression that carp prolactin receptor (PRLr) protein depicts upon seasonal acclimatization supports the hypothesis that PRL and its receptor clearly are involved in the new homeostatic stage that the eurythermal fish needs to survive during the cyclical changes of its habitat. Here, we characterize the first prolactin receptor gene in a teleost and show that its expression is not associated with alternative promoters, unlike in humans and rodents. Using the regulatory region to direct the transcription of green fluorescent protein (GFP) in zebrafish embryos, we mapped the appearance of this hormone receptor during fish development. This is the first report identifying a fish prolactin receptor gene expressing transcript isoforms encoding for short forms of the protein (45 kDa). These have been found in osmoregulatory tissues of the carp and are regulated in connection with the seasonal acclimatization of the fish.

Induction and specification of cranial placodes

Cranial placodes are specialized regions of the ectoderm, which give rise to various sensory ganglia and contribute to the pituitary gland and sensory organs of the vertebrate head. They include the adenohypophyseal, olfactory, lens, trigeminal, and profundal placodes, a series of epibranchial placodes, an otic placode, and a series of lateral line placodes. After a long period of neglect, recent years have seen a resurgence of interest in placode induction and specification. There is increasing evidence that all placodes despite their different developmental fates originate from a common panplacodal primordium around the neural plate. This common primordium is defined by the expression of transcription factors of the Six1/2, Six4/5, and Eya families, which later continue to be expressed in all placodes and appear to promote generic placodal properties such as proliferation, the capacity for morphogenetic movements, and neuronal differentiation. A large number of other transcription factors are expressed in subdomains of the panplacodal primordium and appear to contribute to the specification of particular subsets of placodes. This review first provides a brief overview of different cranial placodes and then synthesizes evidence for the common origin of all placodes from a panplacodal primordium. The role of various transcription factors for the development of the different placodes is addressed next, and it is discussed how individual placodes may be specified and compartmentalized within the panplacodal primordium. Finally, tissues and signals involved in placode induction are summarized with a special focus on induction of the panplacodal primordium itself (generic placode induction) and its relation to neural induction and neural crest induction. Integrating current data, new models of generic placode induction and of combinatorial placode specification are presented.

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

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

Eya1 is required for lineage-specific differentiation, but not for cell survival in the zebrafish adenohypophysis

The homeodomain transcription factor Six1 and its modulator, the protein phosphatase Eya1, cooperate to promote cell differentiation and survival during mouse organ development. Here, we studied the effects caused by loss of eya1 and six1 function on pituitary development in zebrafish. eya1 and six1 are co-expressed in all adenohypophyseal cells. Nevertheless, eya1 (aal, dog) mutants show lineage-specific defects, defining corticotropes, melanotropes, and gonadotropes as an Eya1-dependent lineage, which is complementary to the Pit1 lineage. Furthermore, eya1 is required for maintenance of pit1 expression, leading to subsequent loss of cognate hormone gene expression in thyrotropes and somatotropes of mutant embryos, whereas prolactin expression in lactotropes persists. In contrast to other organs, adenohypophyseal cells of eya1 mutants do not become apoptotic, and the adenohypophysis remains at rather normal size. Also, cells do not trans-differentiate, as in the case of pit1 mutants, but display morphological features characteristic for nonsecretory cells. Some of the adenohypophyseal defects of eya1 mutants are moderately enhanced in combination with antisense-mediated loss of Six1 function, which per se does not affect pituitary cell differentiation. In conclusion, this is the first report of an essential role of Eya1 during pituitary development in vertebrates. Eya1 is required for lineage-specific differentiation of adenohypophyseal cells, but not for their survival, thereby uncoupling the differentiation-promoting and anti-apoptotic effects of Eya proteins seen in other tissues.

Bone morphogenetic protein-4 inhibits corticotroph tumor cells: involvement in the retinoic acid inhibitory action

The molecular mechanisms governing the pathogenesis of ACTH-secreting pituitary adenomas are still obscure. Furthermore, the pharmacological treatment of these tumors is limited. In this study, we report that bone morphogenetic protein-4 (BMP-4) is expressed in the corticotrophs of human normal adenohypophysis and its expression is reduced in corticotrophinomas obtained from Cushing's patients compared with the normal pituitary. BMP-4 treatment of AtT-20 mouse corticotrophinoma cells has an inhibitory effect on ACTH secretion and cell proliferation. AtT-20 cells stably transfected with a dominant-negative form of the BMP-4 signal cotransducer Smad-4 or the BMP-4 inhibitor noggin have increased tumorigenicity in nude mice, showing that BMP-4 has an inhibitory role on corticotroph tumorigenesis in vivo. Because the activation of the retinoic acid receptor has an inhibitory action on Cushing's disease progression, we analyzed the putative interaction of these two pathways. Indeed, retinoic acid induces both BMP-4 transcription and expression and its antiproliferative action is blocked in Smad-4dn- and noggin-transfected Att-20 cells that do not respond to BMP-4. Therefore, retinoic acid induces BMP-4, which participates in the antiproliferative effects of retinoic acid. This new mechanism is a potential target for therapeutic approaches for Cushing's disease.

Evolutionary origins of vertebrate placodes: insights from developmental studies and from comparisons with other deuterostomes

Ectodermal placodes comprise the adenohypophyseal, olfactory, lens, profundal, trigeminal, otic, lateral line, and epibranchial placodes. The first part of this review presents a brief overview of placode development. Placodes give rise to a variety of cell types and contribute to many sensory organs and ganglia of the vertebrate head. While different placodes differ with respect to location and derivative cell types, all appear to originate from a common panplacodal primordium, induced at the anterior neural plate border by a combination of mesodermal and neural signals and defined by the expression of Six1, Six4, and Eya genes. Evidence from mouse and zebrafish mutants suggests that these genes promote generic placodal properties such as cell proliferation, cell shape changes, and specification of neurons. The common developmental origin of placodes suggests that all placodes may have evolved in several steps from a common precursor. The second part of this review summarizes our current knowledge of placode evolution. Although placodes (like neural crest cells) have been proposed to be evolutionary novelties of vertebrates, recent studies in ascidians and amphioxus have proposed that some placodes originated earlier in the chordate lineage. However, while the origin of several cellular and molecular components of placodes (e.g., regionalized expression domains of transcription factors and some neuronal or neurosecretory cell types) clearly predates the origin of vertebrates, there is presently little evidence that these components are integrated into placodes in protochordates. A scenario is presented according to which all placodes evolved from an adenohypophyseal-olfactory protoplacode, which may have originated in the vertebrate ancestor from the anlage of a rostral neurosecretory organ (surviving as Hatschek's pit in present-day amphioxus).

Embryonic versus blastogenetic development in the compound ascidian Botryllus schlosseri: insights from Pitx expression patterns

The colonial ascidians reproduce either sexually or asexually, having evolved a rich variety of modes of propagative development. During embryogenesis, the fertilized egg develops into a swimming tadpole larva that subsequently metamorphoses into a sessile oozooid. Clonal individuals (blastozooids), resembling oozooids, are formed from few bud-forming multipotent somatic cells, following a wide range of ways that seem to characterize each family of this class. Here, we compare these two developmental processes in the compound ascidian species Botryllus schlosseri to determine whether similar gene activities are used during embryogenesis/metamorphosis and recruited in the asexual development. We analyzed expression of Pitx, a Paired-related homeobox gene. Pitx genes are key developmental genes in vertebrates, and their expression is reported to be conserved in chordate stomodea and in the establishment of left/right asymmetries. Here, we report full-length cDNA cloning of a B. schlosseri Pitx ortholog (Bs-Pitx) and expression analysis during both embryo/metamorphosis and blastogenesis. During organogenesis of both developmental sequences, Bs-Pitx was detected in identical domains: the stomodeum/neural complex and asymmetrically in the left digestive system. In striking contrast, expression patterns at early stages differ deeply. These observations provide the first evidence for a key developmental gene being deployed in essentially similar ways in two different developmental sequences that eventually give rise to similar zooids.

Endocrinology of protochordates

Large-scale gene duplications occurred early in the vertebrate lineage after the split with protochordates. Thus, protochordate hormones and their receptors, transcription factors, and signaling pathways may be the foundation for the endocrine system in vertebrates. A number of hormones have been identified including cionin, a likely ancestor of cholecytokinin (CCK) and gastrin. Both insulin and insulin-like growth hormone (IGF) have been identified in separate cDNAs in a tunicate, whereas only a single insulin-like peptide was found in amphioxus. In tunicates, nine distinct forms of gonadotropin-releasing hormone (GnRH) are shown to induce gamete release, even though a pituitary gland and sex steroids are lacking. In both tunicates and amphioxus, there is evidence of some components of a thyroid system, but the lack of a sequenced genome for amphioxus has slowed progress in the structural identification of its hormones. Immunocytochemistry has been used to tentatively identify a number of hormones in protochordates, but structural and functional studies are needed. For receptors, protochordates have many vertebrate homologs of nuclear receptors, such as the thyroid, retinoic acid, and retinoid X receptors. Also, tunicates have cell surface receptors including the G-protein-coupled type, such as β-adrenergic, putative endocannabinoid, cionin (CCK-like), and two GnRH receptors. Several tyrosine kinase receptors include two epidermal growth factor (EGF) receptors (tunicates) and an insulin/IGF receptor (amphioxus). Interestingly, neither steroid receptors nor a full complement of enzymes for synthesis of sex steroids are encoded in the Ciona genome. Tunicates appear to have some but not all of the necessary molecules to develop a vertebrate-like pituitary or complete thyroid system.

Pituitary expression of type I and type II glucocorticoid receptors during chicken embryonic development and their involvement in growth hormone cell differentiation

Glucocorticoids can induce somatotroph differentiation in vitro and in vivo during chick embryonic and rat fetal development. In the present study, we identified the nuclear receptors involved in somatotroph differentiation and examined their ontogeny and cellular distribution during pituitary development in the chicken embryo. Several steroids were tested for their ability to induce GH cell differentiation. Only glucocorticoids and aldosterone were effective at low nanomolar concentrations, suggesting involvement of both type I (mineralocorticoid) and type II (glucocorticoid) receptors (MR and GR, respectively). ZK98299 and spironolactone (GR and MR antagonists, respectively) when used alone were unable to block corticosterone or aldosterone (2 nm)-induced somatotroph differentiation. However, ZK98299 and spironolactone in combination abolished corticosterone or aldosterone (2 nm)-induced somatotroph differentiation. When used separately, both antagonists attenuated induction of GH mRNA by corticosterone. Spironolactone alone blocked somatotroph differentiation induced by 0.2 nm corticosterone or aldosterone, indicating that corticosteroids at subnanomolar concentrations act only through the MR. GR protein was detected in pituitary extracts as early as embryonic d 8, whereas MR protein was readily detectable only around d 12. GR were expressed in greater than 95% of all pituitary cells, whereas MR were expressed in about 40% of all pituitary cells. Dual-label immunofluorescence revealed that the majority of somatotrophs on d 12 expressed MR. Given the high affinity of corticosteroids for MR and that corticosteroid concentrations during embryonic development are in the subnanomolar range, expression of MR may constitute a significant developmental event during somatotroph differentiation.

Genetic analysis of adenohypophysis formation in zebrafish

The adenohypophysis consists of at least six different cell types, somatotropes, lactotropes, thyrotropes, melanotropes, corticotropes, and gonadotropes. In mouse, cloning of spontaneous mutations and gene targeting has revealed multiple genes required for different steps of adenohypophysis development. Here, we report the results of a systematic search for genes required for adenohypophysis formation and patterning in zebrafish. By screening F3 offspring of N-ethyl-N-nitrosourea-mutagenized founder fish, we isolated eleven mutants with absent or reduced expression of GH, the product of somatotropes, but a normally developing hypothalamus. Of such mutants, eight were further analyzed and mapped. They define four genes essential for different steps of adenohypophysis development. Two of them, lia and pia, affect the entire adenohypophysis, whereas the other two are required for a subset of adenohypophyseal cell types only. The third gene is zebrafish pit1 and is required for lactotropes, thyrotropes, and somatotropes, similar to its mouse ortholog, whereas the fourth, aal, is required for corticotropes, melanotropes, thyrotropes, and somatotropes, but not lactotropes. In conclusion, the isolated zebrafish mutants confirm principles of adenohypophysis development revealed in mouse, thereby demonstrating the high degree of molecular and mechanistic conservation among the different vertebrate species. In addition, they point to thus far unknown features of adenohypophysis development, such as the existence of a new lineage of pituitary cells, which partially overlaps with the Pit1 lineage. Positional cloning of the lia, pia, and aal genes might reveal novel regulators of vertebrate pituitary development.

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

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

Neuropeptides in anterior pituitary development

Recent studies using biotechnological methods have achieved significant advances in our knowledge of molecular mechanisms underlying pituitary gland development and the differentiation of pituitary cytotypes. A large number of neuropeptides have been reported in the adult pituitary gland as well as in the central and peripheral nervous system. The early presence of neuropeptides during pituitary development is reviewed here. Neuromedin U (NmU), galanin and the polypeptide 7B2 have been localised to different endocrine cells of the gland. Their expression seems to be manifold even though it is temporally and spatially regulated. There is now firm immunocytochemical evidence that neuropeptides are present during morphogenesis of the pituitary and can be present simultaneously with all pituitary hormones.

Regulation of the intronic promoter of rat estrogen receptor alpha gene, responsible for truncated estrogen receptor product-1 expression

We have characterized the intronic promoter of the rat estrogen receptor (ER) alpha gene, responsible for the lactotrope-specific truncated ER product (TERP)-1 isoform expression. Transcriptional regulation was investigated by transient transfections using 5'-deletion constructs. TERP promoter constructs were highly active in MMQ cells, a pure lactotrope cell line, whereas a low basal activity was detected in alphaT3-1 gonadotrope cells or in COS-7 monkey kidney cells. Serial deletion analysis revealed that 1) a minimal -693-bp region encompassing the TATA box is sufficient to allow lactotrope-specific expression; 2) the promoter contains strong positive cis-acting elements both in the distal and proximal regions, and 3) the region spanning the -1698/-1194 region includes repressor elements. Transient transfection studies, EMSAs, and gel shifts demonstrated that estrogen activates the TERP promoter via an estrogen-responsive element (ERE1) located within the proximal region. Mutation of ERE1 site completely abolishes the estradiol-dependent transcription, indicating that ERE1 site is sufficient to confer estrogen responsiveness to TERP promoter. In addition, ERalpha action was synergized by transfection of the pituitary-specific factor Pit-1. EMSAs showed that a single Pit-1 DNA binding element in the vicinity of the TATA box is sufficient to confer response by the TERP promoter. In conclusion, we demonstrated, for the first time, that TERP promoter regulation involves ERE and Pit-1 cis-elements and corresponding trans-acting factors, which could play a role in the physiological changes that occur in TERP-1 transcription in lactotrope cells.

Adenohypophysis formation in the zebrafish and its dependence on sonic hedgehog

Formation of the adenohypophysis in mammalian embryos occurs via an invagination of the oral ectoderm to form Rathke's pouch, which becomes exposed to opposing dorsoventral gradients of signaling proteins governing specification of the different hormone-producing pituitary cell types. One signal promoting pituitary cell proliferation and differentiation to ventral cell types is Sonic hedgehog (Shh) from the oral ectoderm. To study pituitary formation and patterning in zebrafish, we cloned four cDNAs encoding different pituitary hormones, prolactin (prl), proopiomelancortin (pomc), thyroid stimulating hormone (tsh), and growth hormone (gh), and analyzed their expression patterns relative to that of the pituitary marker lim3. prl and pomc start to be expressed at the lateral edges of the lim3 expression domain, before pituitary cells move into the head. This indicates that patterning of the pituitary anlage and terminal differentiation of pituitary cells starts while cells are still organized in a placodal fashion at the anterior edge of the developing brain. Following the expression pattern of prl and pomc during development, we show that no pituitary-specific invagination equivalent to Rathke's pouch formation takes place. Rather, pituitary cells move inwards together with stomodeal cells during oral cavity formation, with medial cells of the placode ending up posterior and lateral cells ending up anterior, resulting in an anterior-posterior, rather than a dorsoventral, patterning of the adenohypophysis. Carrying out loss- and gain-of-function experiments, we show that Shh from the ventral diencephalon plays a crucial role during induction, patterning, and growth of the zebrafish adenohypophysis. The phenotypes are very similar to those obtained upon pituitary-specific inactivation or overexpression of Shh in mouse embryo, suggesting that the role of Shh during pituitary development has been largely conserved between fish and mice, despite the different modes of pituitary formation in the two vertebrate classes.

Current approaches for deciphering the molecular basis of combined anterior pituitary hormone deficiency in humans

This review focuses on the general strategies currently used to decipher the molecular bases of combined pituitary hormone deficiency (CPHD) of genetic origin. By summarizing illustrative approaches that turned out to be successful for identifying an increasing number of genes involved in CPHD in the human, this article consider predictable obstacles specific to the investigation of these rare and heterogeneous conditions, while underlining the previously unsuspected roles of several of these genes during the development of extrapituitary structures.

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.

Multiple mechanisms for Pitx-1 transactivation of a luteinizing hormone beta subunit gene

The pituitary homeobox factor-1 (Pitx-1) transactivates a number of pituitary-specific genes through direct interaction with other specific transcription factors. We demonstrate here that Pitx-1 plays a crucial role in the regulation of the Chinook salmon luteinizing hormone beta gene promoter through a number of novel mechanisms. On the proximal promoter its action involves a synergistic effect with steroidogenic factor-1 (SF-1) alone or in combination with the estrogen receptor; promoter activity being induced by 9- or 35-fold over controls, respectively. Further upstream, a series of four Pitx-1 response elements (located between 1366 and 1506 bp from the transcriptional start site) is also involved in regulating the promoter activity. The two distal sequences have the greatest effect on the basal activity and are also essential for the gonadotropin-releasing hormone (GnRH) response. Mammalian two-hybrid assays revealed that Pitx-1 can homodimerize. Moreover, circular permutation assays indicate that binding of Pitx-1 to more than one response element induces conformational changes of the target DNA. This constitutes an additional mechanism through which Pitx-1 can mediate transactivation of this gene, allowing the demonstrated interaction of proximal response elements and distal enhancers, thus facilitating the maximal GnRH response that was seen in the longer promoter constructs. Our research also indicates that Pitx-1 is phosphorylated on three residues when bound to the DNA.

Complementary expression of IGF-II and IGFBP-5 during anterior pituitary development

The specification of the five individual hormone-secreting cell types in the anterior pituitary requires a series of sequential cell fate decisions. We have immortalized cells at several stages along this pathway of pituitary differentiation. Here, we present analysis of differences in gene expression between an anterior pituitary precursor cell line, alphaT1-1, and an immature gonadotrope cell line, alphaT3-1, identified by using cDNA subtraction. Messenger RNA expression of members of the insulin-like growth factor signaling system, IGF-II and IGFBP-5, was found in the alphaT1-1 precursor cell line, but not in the more differentiated cell line, alphaT3-1. This inferred stage specificity was confirmed in the mouse embryo by using in situ hybridization on embryonic days e10.5 through e18.5. Expression of IGF-II and IGFBP-5 mRNAs was both temporally and spatially regulated during pituitary development. IGF-II was highly expressed in the epithelium surrounding Rathke's pouch at e10.5, while IGFBP-5 expression was restricted to the adjacent oral epithelium. At e11.5 (represented by alphaT1-1), IGF-II was expressed throughout the pouch, but was coexpressed with IGFBP-5 and alpha-subunit in the ventral portion of the pouch epithelium. On e12.5, the two mRNAs were expressed in opposing dorsoventral (IGF-II) and ventrodorsal (IGFBP-5) patterns, with IGF-II excluded from the rostral, alpha-subunit-expressing region. A decrease of both mRNAs was observed at e14.5 (equivalent to alphaT3-1), with IGF-II levels low and IGFBP-5 concentrated in the anterior pituitary rostral tip. These findings suggest that the timing of IGF-II expression and regulation of its accessibility by IGFBP-5 may play a role in anterior pituitary differentiation, survival, and/or proliferation.

Pitx genes in Tunicates provide new molecular insight into the evolutionary origin of pituitary

We have initiated a project aimed at documenting molecular and cellular changes underlying the emergence of the hypothalamo-hypophyseal axis in Chordates. Considering the phylogenetic position of Tunicates and the 'pan-hypophyseal' expression pattern of Pitx genes in Vertebrate pituitary, we searched for a Pitx-related homeobox gene in the ascidian Ciona intestinalis, and identified Ci-Pitx (ona intestinalis uitary homeobo gene). We also isolated Cs-Pitx and Bs-Pitx, the Ci-Pitx respective counterparts of Ciona savignyi and Botryllus schlosseri, two other Tunicate species. Ci-Pitx mRNA encodes a putative protein exhibiting the diagnostic K50-Paired-class homeodomain and a conserved C-terminal Aristaless domain. Embryonic expression pattern of Ci-Pitx revealed a conserved expression domain in the anterior neural ridge and subsequently in the pharyngeal primordium, defined in Vertebrates as the stomodeal ectomere, which encompasses the presumptive pituitary territory. This shows that expression at early steps of pituitary development is a feature of Pitx-related genes that was already present in the last common ancestor of Chordates.

Evidence for nodose ganglion as the source of innervation to the anterior lobe of the pituitary gland

Recent studies have provided convincing evidence for the presence of peptidergic nerve fibers in the pituitary anterior lobe in several animal species. This study was aimed at elucidating the origin of this innervation by neuroanatomical tracing, denervation experiments, and immunohistochemistry. Immunohistochemistry against substance P and growth-associated protein 43 revealed a dense fiber plexus within the anterior lobe, and these markers were mostly colocalized. Retrograde tracing with Fluorogold from the pituitary gland stained neurons in the hypothalamus, superior cervical ganglia and the nodose ganglia. None of the Fluorogold-labelled neurons in the hypothalamus or superior cervical ganglion were substance P-immunoreactive, while many of the neuronal cell bodies in the nodose ganglion exhibited substance P immunoreactivity. There were no Fluorogold-labelled neurons in the trigeminal, otic or cervical dorsal root ganglia. Surgical transection of the pituitary stalk or bilateral removal of the superior cervical ganglion did not abolish the anterior lobe nerve fibers, and anterograde tracing with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindo-carbocyanine perchlorate from the pituitary stalk failed to stain any nerve fibers within the anterior lobe. Our findings suggest that the nodose ganglion neurons likely innervate the pituitary anterior lobe, while neither hypothalamus nor sympathetic superior cervical ganglion may be a source of this innervation. By showing a distinct neuronal system in the pituitary anterior lobe our findings (i) support the previous functional studies demonstrating a distinct regulation of the morphology of the anterior lobe innervation by hormonal changes, and (ii) suggest that the innervation of the pituitary anterior lobe is a part of the visceral innervation by the vagus nerve rather than a part of the other intracranial innervation. These findings provide a neuroanatomic basis for the reported observations about the neural regulation of the pituitary anterior lobe.

Expression and localization of the homeodomain-containing protein HEX in human thyroid tumors

Homeobox genes are involved in neoplastic transformation of both epithelial and hemopoietic tissues. The divergent homeobox gene HEX is expressed in the anterior visceral endoderm during early mouse development and in some adult tissues of endodermal origin, including liver and thyroid. Whereas a role in leukemyogenesis has been proposed already, few data are available on the involvement of HEX in human epithelial tumors. Herein, we analyzed HEX expression and subcellular localization in a series of 55 human thyroid tumors and in several tumoral cell lines. HEX mRNA was detected by RT-PCR either in normal tissues or in thyroid adenomas and differentiated (papillary and follicular) carcinomas. HEX mRNA was also expressed in most undifferentiated carcinomas. Subcellular localization of HEX protein was investigated by immunohistochemistry. In normal tissues and adenomas, HEX protein was present both in nucleus and cytoplasm. In contrast, both differentiated and undifferentiated carcinomas, as well as the tumoral cell lines investigated, showed HEX protein only in the cytoplasm. These findings suggest that regulation of HEX entry in the nucleus of thyrocytes may represent a critical step during human thyroid tumorigenesis.

PROP1 gene screening in patients with multiple pituitary hormone deficiency reveals two sites of hypermutability and a high incidence of corticotroph deficiency

Alterations of the gene encoding the pituitary transcription factor PROP1 were associated with congenital forms of multiple pituitary hormone deficiencies in several families. Among 23 patients with multiple pituitary hormone deficiencies screened for a PROP1 gene abnormality, nine belonging to eight unrelated families had homozygous PROP1 gene defects. All mutations were located in exon 2 and affected only two different sites: a homozygous AG deletion at codons 99/100/101 (n = 5); homozygous point mutations affecting codon 73: R73C (n = 2) or R73H (n = 1), and a R73C/R99X double-heterozygous mutation (n = 1). R73H and R99X were never described. All patients were born to unaffected parents, and consanguinity was documented in two patients. They had complete GH, LH-FSH, and TSH deficiencies and normal basal levels of PRL. Delayed ACTH deficiency was diagnosed in four of nine patients. At magnetic resonance imaging the anterior pituitary was hypoplastic in seven patients and hyperplastic in two. This study found two novel mutations (R73H and R99X) and underlines the high incidence of PROP1 gene alterations in patients with multiple pituitary hormone deficiencies. A corticotroph deficiency was frequently observed in association with GH, TSH, and gonadotropin deficiencies and should be carefully sought during follow-up.

Vertebrate cranial placodes I. Embryonic induction

Cranial placodes are focal regions of thickened ectoderm in the head of vertebrate embryos that give rise to a wide variety of cell types, including elements of the paired sense organs and neurons in cranial sensory ganglia. They are essential for the formation of much of the cranial sensory nervous system. Although relatively neglected today, interest in placodes has recently been reawakened with the isolation of molecular markers for different stages in their development. This has enabled a more finely tuned approach to the understanding of placode induction and development and in some cases has resulted in the isolation of inducing molecules for particular placodes. Both morphological and molecular data support the existence of a preplacodal domain within the cranial neural plate border region. Nonetheless, multiple tissues and molecules (where known) are involved in placode induction, and each individual placode is induced at different times by a different combination of these tissues, consistent with their diverse fates. Spatiotemporal changes in competence are also important in placode induction. Here, we have tried to provide a comprehensive review that synthesises the highlights of a century of classical experimental research, together with more modern evidence for the tissues and molecules involved in the induction of each placode.

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.

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.

Roles of growth hormone and insulin-like growth factor 1 in mouse postnatal growth

To examine the relationship between growth hormone (GH) and insulin-like growth factor 1 (IGF1) in controlling postnatal growth, we performed a comparative analysis of dwarfing phenotypes manifested in mouse mutants lacking GH receptor, IGF1, or both. This genetic study has provided conclusive evidence demonstrating that GH and IGF1 promote postnatal growth by both independent and common functions, as the growth retardation of double Ghr/Igf1 nullizygotes is more severe than that observed with either class of single mutant. In fact, the body weight of these double-mutant mice is only approximately 17% of normal and, in absolute magnitude ( approximately 5 g), only twice that of the smallest known mammal. Thus, the growth control pathway in which the components of the GH/IGF1 signaling systems participate constitutes the major determinant of body size. To complement this conclusion mainly based on extensive growth curve analyses, we also present details concerning the involvement of the GH/IGF1 axis in linear growth derived by a developmental study of long bone ossification in the mutants.

Biochemical and genetic characterization of the porcine Prophet of Pit-1 pituitary transcription factor

Prophet of Pit-1 (Prop-1) is a paired class homeodomain transcription factor that is specifically expressed in the pituitary gland. Mutations in the Prop-1 gene cause compound pituitary diseases in mouse models and human patients. We have cloned and analyzed the porcine ortholog of Prop-1. Analysis of cDNAs revealed that the porcine Prop-1 sequence is similar to the mouse and human proteins within the homeodomain and carboxyl terminus, but the amino terminus is poorly conserved. The Prop-1 gene consists of three exons and two introns and spans 3.8 kilobases of genomic DNA. In addition, we mapped Prop-1 to the q arm of pig chromosome two. During development, Prop-1 is expressed at the time of pituitary organogenesis. In the adult, expression was observed at low levels only in the pituitary gland. The porcine Prop-1 protein displays similar biochemical, DNA binding, and transcriptional activities to human PROP-1. We conclude that, although the structural divergence between the porcine and human PROP-1 molecules may indicate some distinct functions, the porcine Prop-1 gene encodes a pituitary transcription factor with similar overall activities to the human ortholog.

Fibroblast growth factor signaling is required for the proliferation and patterning of progenitor cells in the developing anterior pituitary

The proliferation and patterning of progenitor cells in the anterior pituitary require signals derived from the neuroepithelium of the juxtaposed infundibulum. The infundibulum expresses Fibroblast growth factor (Fgf) 8 and Fgf 18, and FGFs can mimic some of the activities of the infundibulum. The requirement for FGF signaling during growth and patterning of the anterior pituitary has not, however, been established. By blocking FGF receptor signaling in explants of the anterior pituitary cultured in vitro we provide evidence that FGF signaling derived from the infundibulum is required for the proliferation and patterning of progenitor cells in the anterior pituitary.