Molecular cloning and characterization of NESP55, a novel chromogranin-like precursor of a peptide with 5-HT1B receptor antagonist activity

Frequency of de novo variants and parental mosaicism in families with inactivating PTH/PTHrP signaling disorder type 2

Objective

iPPSD2 (which includes PHP1A and PPHP/POH) is a rare inherited autosomal dominant endocrine disorder caused by inactivating GNAS pathogenic variants. A high percentage of de novo cases has been suggested. In rare cases, parental mosaicism has been described, but its real frequency is unknown.

Design

A retrospective study including a series of 95 genetically confirmed iPPSD2 probands.

Methods

The frequency of de novo cases was evaluated and the distribution of the type of variants was compared according to the type of inheritance. The putative involved allele was determined by reverse transcriptase PCR (RT-PCR) or allele specific oligonucleotide RT-PCR (ASO-RT-PCR). The possibility of GNAS mosaicism was studied by next-generation sequencing (NGS) on the corresponding parental DNA.

Results

In 41 patients the variant was of de novo origin and in 24 the origin could not be established. In both cases 66.67% of variants generated a truncated or absent protein whereas the rest of the variants were missense or in-frame deletion/duplication. Parental origin was studied in 45 of those patients and determined in 35. Curiously, the percentage of de novo variants at the paternal allele was higher than when paternally inherited (31.1% vs 6.67%). NGS detected mosaicism in three independent families: one from paternal DNA (allelic ratio 10%) and two from maternal DNA (allelic ratio 10% and 2%).

Conclusion

De novo pathogenic variants are frequent in iPPSD2 (around 45%). Parental mosaicism is infrequent (8.11%) but should be analyzed with NGS, taking into account its importance in genetic counselling.

Role and function of granin proteins in diabetes mellitus

The granin glycoprotein family consists of nine acidic proteins; chromogranin A (CgA), chromogranin B (CgB), and secretogranin II–VIII. They are produced by a wide range of neuronal, neuroendocrine, and endocrine cells throughout the human body. Their major intracellular function is to sort peptides and proteins into secretory granules, but their cleavage products also take part in the extracellular regulation of diverse biological processes. The contribution of granins to carbohydrate metabolism and diabetes mellitus is a recent research area. CgA is associated with glucose homeostasis and the progression of type 1 diabetes. WE-14, CgA_10-19, and CgA_43-52 are peptide derivates of CgA, and act as CD4⁺ or CD8⁺ autoantigens in type 1 diabetes, whereas pancreastatin (PST) and catestatin have regulatory effects in carbohydrate metabolism. Furthermore, PST is related to gestational and type 2 diabetes. CgB has a crucial role in physiological insulin secretion. Secretogranins II and III have angiogenic activity in diabetic retinopathy (DR), and are novel targets in recent DR studies. Ongoing studies are beginning to investigate the potential use of granin derivatives as drugs to treat diabetes based on the divergent relationships between granins and different types of diabetes.

Molecular Definition of Pseudohypoparathyroidism Variants

Pseudohypoparathyroidism (PHP) and pseudopseudohypoparathyroidism (PPHP) are caused by mutations and/or epigenetic changes at the complex GNAS locus on chromosome 20q13.3 that undergoes parent-specific methylation changes at several differentially methylated regions (DMRs). GNAS encodes the alpha-subunit of the stimulatory G protein (Gsα) and several splice variants thereof. PHP type Ia (PHP1A) is caused by heterozygous inactivating mutations involving the maternal exons 1-13. Heterozygosity of these maternal GNAS mutations cause PTH-resistant hypocalcemia and hyperphosphatemia because paternal Gsα expression is suppressed in certain organs thus leading to little or no Gsα protein in the proximal renal tubules and other tissues. Besides biochemical abnormalities, PHP1A patients show developmental abnormalities, referred to as Albright's hereditary osteodystrophy (AHO). Some, but not all of these AHO features are encountered also in patients affected by PPHP, who carry paternal Gsα-specific mutations and typically show no laboratory abnormalities. Autosomal dominant PHP type Ib (AD-PHP1B) is caused by heterozygous maternal deletions within GNAS or STX16, which are associated with loss of methylation at the A/B DMR alone or at all maternally methylated GNAS exons. Loss of methylation of exon A/B and the resulting biallelic expression of A/B transcript reduces Gsα expression thus leading to hormonal resistance. Epigenetic changes at all differentially methylated GNAS regions are also observed in sporadic PHP1B, which is the most frequent PHP1B variant. However, this disease variant remains unresolved at the molecular level, except for rare cases with paternal uniparental isodisomy or heterodisomy of chromosome 20q (patUPD20q).

Heterotopic ossification: Mechanistic insights and clinical challenges

Bone formation is exquisitely controlled both spatially and temporally. Heterotopic ossification (HO) is pathological bone formation in soft tissues that often leads to deleterious outcomes. Inherited genetic forms of HO can be life-threatening and can happen as early as in infancy. However, there is currently no effective treatment for HO as the underlying cellular and molecular mechanisms have not been completely elucidated. Trauma-induced non-genetic forms of HO often occur as a common complication after surgeries or accidents, and the location of HO occurrence largely determines the symptom and outcome. While it has been difficult to determine the complicated factors causing HO, recent advancement in identifying cellular and molecular mechanism causing the genetic forms of HO may provide important insights in all HO. Here in this review, we summarize recent studies on HO to provide a current status of both clinical options of HO treatments and mechanical understanding of HO.

Impulsive Choice in Mice Lacking Paternal Expression of Grb10 Suggests Intragenomic Conflict in Behavior

The imprinted gene Grb10 is expressed in the brain from the paternal copy only. Here, Dent et al. show that paternal Grb10 regulates impulsive choices, i.e. whether an animal chooses a smaller food reward...

Imprinted genes are expressed from one parental allele only as a consequence of epigenetic events that take place in the mammalian germ line and are thought to have evolved through intragenomic conflict between parental alleles. We demonstrate, for the first time, oppositional effects of imprinted genes on brain and behavior. Specifically, we show that mice lacking paternal Grb10 make fewer impulsive choices, with no dissociable effects on a separate measure of impulsive action. Taken together with previous work showing that mice lacking maternal Nesp55 make more impulsive choices, this suggests that impulsive choice behavior is a substrate for the action of genomic imprinting. Moreover, the contrasting effect of these two genes suggests that impulsive choices are subject to intragenomic conflict and that maternal and paternal interests pull this behavior in opposite directions. Finally, these data may also indicate that an imbalance in expression of imprinted genes contributes to pathological conditions such as gambling and drug addiction, where impulsive behavior becomes maladaptive.

Accuracy and Clinical Correlates of Two Different Methods for Chromogranin A Assay in Neuroendocrine Tumors

Measurement of chromogranin A (CgA) plays a major role in the management of neuroendocrine tumors (NET); however, reliable assaying of CgA is made difficult by the rapid hydrolysis following its release into the bloodstream. This study was aimed at the assessment of two assays for CgA in NET patients. CgA was measured in 93 patients by means of an enzyme-linked immunosorbent assay (ELISA) and an immunoradiometric assay (IRMA). The specificity and sensitivity of CgA were evaluated in relation to tumor histology. The clinical accuracy of the two assays was evaluated by receiver-operating characteristic (ROC) curve analysis. Regression analysis demonstrated different immunoreactivity for CgA of the antibodies used in the two kits (r=0.61). The two assays had different accuracy also in classifying patients according to their clinical condition (91% vs 64% specificity and 79% vs 79% sensitivity for the ELISA and IRMA assay, respectively) and tumor histology (81% vs 85% sensitivity for the ELISA and IRMA assays, respectively, in carcinoids; 92% vs 67% sensitivity for the ELISA and IRMA assays, respectively, in pancreatic islet cell tumors). The different clinical accuracy of the two assays was confirmed by the ROC analysis (AUC=0.90 vs AUC=0.87 for the ELISA and IRMA assays, respectively). In conclusion, because of the poor standardization of the commercially available measurement tools the clinical accuracy of CgA measurement depends on the assay used. This makes it difficult to compare CgA values measured with different kits and affects the clinical accuracy of the different assays for CgA.

Current Nomenclature of Pseudohypoparathyroidism: Inactivating Parathyroid Hormone/Parathyroid Hormone-Related Protein Signaling Disorder

Disorders related to parathyroid hormone (PTH) resistance and PTH signaling pathway impairment are historically classified under the term of pseudohypoparathyroidism (PHP). The disease was first described and named by Fuller Albright and colleagues in 1942. Albright hereditary osteodystrophy (AHO) is described as an associated clinical entity with PHP, characterized by brachydactyly, subcutaneous ossifications, round face, short stature and a stocky build. The classification of PHP is further divided into PHP-Ia, pseudo-PHP (pPHP), PHP-Ib, PHP-Ic and PHP-II according to the presence or absence of AHO, together with an in vivo response to exogenous PTH and the measurement of Gsα protein activity in peripheral erythrocyte membranes in vitro. However, PHP classification fails to differentiate all patients with different clinical and molecular findings for PHP subtypes and classification become more complicated with more recent molecular characterization and new forms having been identified. So far, new classifications have been established by the EuroPHP network to cover all disorders of the PTH receptor and its signaling pathway. Inactivating PTH/PTH-related protein signaling disorder (iPPSD) is the new name proposed for a group of these disorders and which can be further divided into subtypes - iPPSD1 to iPPSD6. These are termed, starting from PTH receptor inactivation mutation (Eiken and Blomstrand dysplasia) as iPPSD1, inactivating Gsα mutations (PHP-Ia, PHP-Ic and pPHP) as iPPSD2, loss of methylation of GNAS DMRs (PHP-Ib) as iPPSD3, PRKAR1A mutations (acrodysostosis type 1) as iPPSD4, PDE4D mutations (acrodysostosis type 2) as iPPSD5 and PDE3A mutations (autosomal dominant hypertension with brachydactyly) as iPPSD6. iPPSDx is reserved for unknown molecular defects and iPPSDn+1 for new molecular defects which are yet to be described. With these new classifications, the aim is to clarify the borders of each different subtype of disease and make the classification according to molecular pathology. The iPPSD group is designed to be expandable and new classifications will readily fit into it as necessary.

Mice maintain predominantly maternal Gαs expression throughout life in brown fat tissue (BAT), but not other tissues

The murine Gnas (human GNAS) locus gives rise to Gαs and different splice variants thereof. The Gαs promoter is not methylated thus allowing biallelic expression in most tissues. In contrast, the alternative first Gnas/GNAS exons and their promoters undergo parent specific methylation, which limits transcription to the non-methylated allele. Pseudohypoparathyroidism type Ia (PHP1A) or type Ib (PHP1B) are caused by heterozygous maternal GNAS mutations suggesting that little or no Gαs is derived in some tissues from the non-mutated paternal GNAS thereby causing hormonal resistance. Previous data had indicated that Gαs is mainly derived from the maternal Gnas allele in brown adipose tissue (BAT) of newborn mice, yet it is biallelically expressed in adult BAT. This suggested that paternal Gαs expression is regulated by an unknown factor(s) that varies considerably with age. To extend these findings, we now used a strain-specific SNP in Gnas exon 11 (rs13460569) for evaluation of parent-specific Gαs expression through the densitometric quantification of BanII-digested RT-PCR products and digital droplet PCR (ddPCR). At all investigated ages, Gαs transcripts were derived in BAT predominantly from the maternal Gnas allele, while kidney and liver showed largely biallelic Gαs expression. Only low or undetectable levels of other paternally Gnas-derived transcripts were observed, making it unlikely that these are involved in regulating paternal Gαs expression. Our findings suggest that a cis-acting factor could be implicated in reducing paternal Gαs expression in BAT and presumably in proximal renal tubules, thereby causing PTH-resistance if the maternal GNAS/Gnas allele is mutated.

The Complex GNAS Imprinted Locus and Mesenchymal Stem Cells Differentiation

All tissues and organs derive from stem cells, which are undifferentiated cells able to differentiate into specialized cells and self-renewal. In mammals, there are embryonic stem cells that generate germ layers, and adult stem cells, which act as a repair system for the body and maintain the normal turnover of regenerative organs. Mesenchymal stem cells (MSCs) are nonhematopoietic adult multipotent cells, which reside in virtually all postnatal organs and tissues, and, under appropriate in vitro conditions, are capable to differentiate into osteogenic, adipogenic, chondrogenic, myogenic, and neurogenic lineages. Their commitment and differentiation depend on several interacting signaling pathways and transcription factors. Most GNAS-based disorders have the common feature of episodic de novo formation of islands of extraskeletal, qualitatively normal, bone in skin and subcutaneous fat. The tissue distribution of these lesions suggests that pathogenesis involves abnormal differentiation of MSCs and/or more committed precursor cells that are present in subcutaneous tissues. Data coming from transgenic mice support the concept that GNAS is a key factor in the regulation of lineage switching between osteoblast and adipocyte fates, and that its role may be to prevent bone formation in tissues where bone should not form. Despite the growing knowledge about the process of heterotopic ossification in rare genetic disorders, the pathophysiological mechanisms by which alterations of cAMP signaling lead to ectopic bone formation in the context of mesenchymal tissues is not fully understood.

Pseudohypoparathyroidism: one gene, several syndromes

Pseudohypoparathyroidism (PHP) and pseudopseudohypoparathyroidism (PPHP) are caused by mutations and/or epigenetic changes at the complex GNAS locus on chromosome 20q13.3 that undergoes parent-specific methylation changes at several sites. GNAS encodes the alpha-subunit of the stimulatory G protein (Gsα) and several splice variants thereof. Heterozygous inactivating mutations involving the maternal GNAS exons 1-13 cause PHP type Ia (PHP1A). Because of much reduced paternal Gsα expression in certain tissues, such as the proximal renal tubules, thyroid, and pituitary, there is little or no Gsα protein in the presence of maternal GNAS mutations, thus leading to PTH-resistant hypocalcemia and hyperphosphatemia. When located on the paternal allele, the same or similar GNAS mutations are the cause of PPHP. Besides biochemical abnormalities, patients affected by PHP1A show developmental abnormalities, referred to as Albrights hereditary osteodystrophy (AHO). Some, but not all of these AHO features are encountered also in patients affected by PPHP, who typically show no laboratory abnormalities. Autosomal dominant PHP type Ib (AD-PHP1B) is caused by heterozygous maternal deletions within GNAS or STX16, which are associated with loss-of-methylation (LOM) at exon A/B alone or at all maternally methylated GNAS exons. LOM at exon A/B and the resulting biallelic expression of A/B transcripts reduces Gsα expression, thus leading to hormonal resistance. Epigenetic changes at all differentially methylated GNAS regions are also observed in sporadic PHP1B, the most frequent disease variant, which remains unresolved at the molecular level, except for rare cases with paternal uniparental isodisomy or heterodisomy of chromosome 20q (patUPD20q).

Impulsive choices in mice lacking imprinted Nesp55

Genomic imprinting is the process whereby germline epigenetic events lead to parent-of-origin specific monallelic expression of a number of key mammalian genes. The imprinted gene Nesp is expressed from the maternal allele only and encodes for Nesp55 protein. In the brain, Nesp55 is found predominately in discrete areas of the hypothalamus and midbrain. Previously, we have shown that loss of Nesp55 gives rise to alterations in novelty-related behaviour. Here, we extend these findings and demonstrate, using the Nesp^m/+ mouse model, that loss of Nesp55 leads to impulsive choices as measured by a delayed-reinforcement task, whereby Nesp^m/+ mice were less willing to wait for a delayed, larger reward, preferring instead to choose an immediate, smaller reward. These effects were highly specific as performance in another component of impulsive behaviour, the ability to stop a response once started as assayed in the stop-signal reaction time task, was equivalent to controls. We also showed changes in the serotonin system, a key neurotransmitter pathway mediating impulsive behaviour. First, we demonstrated that Nesp55 is co-localized with serotonin and then went on to show that in midbrain regions there were reductions in mRNA expression of the serotonin-specific genes Tph2 and Slc6a4, but not the dopamine-specific gene Th in Nesp^m/+ mice; suggesting an altered serotonergic system could contribute, in part, to the changes in impulsive behaviour. These data provide a novel mode of action for genomic imprinting in the brain and may have implications for pathological conditions characterized by maladaptive response control.

Malignant cell-derived extracellular vesicles express different chromogranin epitopes compared to prostasomes

BACKGROUND

Prostasomes are nanosized extracellular vesicles exocytosed by prostate epithelial cells. They have been assigned many roles propitious to sperm in favor of fertilization. Prostatic cancer cells can also produce and secrete extracellular vesicles.

METHODS

We assessed using ELISA, the surface expression of chromogranin proproteins on prostasomes and malignant extracellular vesicles of four different prostate cancer cell-lines, two hormone sensitive and two hormone refractory. We used a panel of chromogranin A and chromogranin B antibodies against peptides in-between hypothetical cleavage sites along the proproteins.

RESULTS

A diverging pattern of chromogranin peptides was apparent when comparing prostasomes and malignant extracellular vesicles indicating a phenotypical change. We also compared western blot patterns (prostasomes and malignant extracellular vesicles) for selected antibodies that displayed high absorbances in the ELISA. Western blot analyses revealed various cleavage patterns of those proproteins that were analyzed in prostasomes and extracellular vesicles.

CONCLUSION

Chromogranins are constituents of not only prostasomes but also of malignant prostate cell-derived extracellular vesicles with different amino acid sequences exposed at the membrane surface giving rise to a mosaic pattern. These findings may be of relevance for designing new assays for detection or even possible treatment of prostate cancers.

GNAS Spectrum of Disorders

The GNAS complex locus encodes the alpha-subunit of the stimulatory G protein (Gsα), a ubiquitous signaling protein mediating the actions of many hormones, neurotransmitters, and paracrine/autocrine factors via generation of the second messenger cAMP. GNAS gives rise to other gene products, most of which exhibit exclusively monoallelic expression. In contrast, Gsα is expressed biallelically in most tissues; however, paternal Gsα expression is silenced in a small number of tissues through as-yet-poorly understood mechanisms that involve differential methylation within GNAS. Gsα-coding GNAS mutations that lead to diminished Gsα expression and/or function result in Albright's hereditary osteodystrophy (AHO) with or without hormone resistance, i.e., pseudohypoparathyroidism type-Ia/Ic and pseudo-pseudohypoparathyroidism, respectively. Microdeletions that alter GNAS methylation and, thereby, diminish Gsα expression in tissues in which the paternal Gsα allele is normally silenced also cause hormone resistance, which occurs typically in the absence of AHO, a disorder termed pseudohypoparathyroidism type-Ib. Mutations of GNAS that cause constitutive Gsα signaling are found in patients with McCune-Albright syndrome, fibrous dysplasia of bone, and different endocrine and non-endocrine tumors. Clinical features of these diseases depend significantly on the parental allelic origin of the GNAS mutation, reflecting the tissue-specific paternal Gsα silencing. In this article, we review the pathogenesis and the phenotypes of these human diseases.

Transcription driven somatic DNA methylation within the imprinted Gnas cluster

Differential marking of genes in female and male gametes by DNA methylation is essential to genomic imprinting. In female gametes transcription traversing differentially methylated regions (DMRs) is a common requirement for de novo methylation at DMRs. At the imprinted Gnas cluster oocyte specific transcription of a protein-coding transcript, Nesp, is needed for methylation of two DMRs intragenic to Nesp, namely the Nespas-Gnasxl DMR and the Exon1A DMR, thereby enabling expression of the Gnas transcript and repression of the Gnasxl transcript. On the paternal allele, Nesp is repressed, the germline DMRs are unmethylated, Gnas is repressed and Gnasxl is expressed. Using mutant mouse models, we show that on the paternal allele, ectopic transcription of Nesp traversing the intragenic Exon1A DMR (which regulates Gnas expression) results in de novo methylation of the Exon1A DMR and de-repression of Gnas just as on the maternal allele. However, unlike the maternal allele, methylation on the mutant paternal allele occurs post-fertilisation, i.e. in somatic cells. This, to our knowledge is the first example of transcript/transcription driven DNA methylation of an intragenic CpG island, in somatic tissues, suggesting that transcription driven de novo methylation is not restricted to the germline in the mouse. Additionally, Gnasxl is repressed on a paternal chromosome on which Nesp is ectopically expressed. Thus, a paternally inherited Gnas cluster showing ectopic expression of Nesp is “maternalised” in terms of Gnasxl and Gnas expression. We show that these mice have a phenotype similar to mutants with two expressed doses of Gnas and none of Gnasxl.

Maternal inheritance of the Gnas cluster mutation Ex1A-T affects size, implicating NESP55 in growth

Genes subjected to genomic imprinting are often associated with prenatal and postnatal growth. Furthermore, it has been observed that maternally silenced/paternally expressed genes tend to favour offspring growth, whilst paternally silenced/maternally expressed genes will restrict growth. One imprinted cluster in which this has been shown to hold true is the Gnas cluster; of the three proteins expressed from this cluster, two, Gsα and XLαs, have been found to affect postnatal growth in a number of different mouse models. The remaining protein in this cluster, NESP55, has not yet been shown to be involved in growth. We previously described a new mutation, Ex1A-T, which upon paternal transmission resulted in postnatal growth retardation due to loss of imprinting of Gsα and loss of expression of the paternally expressed XLαs. Here we describe maternal inheritance of Ex1A-T which gives rise to a small but highly significant overgrowth phenotype which we attribute to reduction of maternally expressed NESP55.

The GNAS complex locus and human diseases associated with loss-of-function mutations or epimutations within this imprinted gene

GNAS is a complex imprinted locus leading to several different gene products that show exclusive monoallelic expression. GNAS also encodes the α-subunit of the stimulatory G protein (Gsα), a ubiquitously expressed signaling protein that is essential for the actions of many hormones and other endogenous molecules. Gsα is expressed biallelically in most tissues but its expression is silenced from the paternal allele in a small number of tissues. The tissue-specific paternal silencing of Gsα results in different parent-of-origin-specific phenotypes in patients who carry inactivating GNAS mutations. In this paper, we review the GNAS complex locus and discuss how disruption of Gsα expression and the expression of other GNAS products shape the phenotypes of human disorders caused by mutations in this gene.

Non-Coding RNAs at the Gnas and Snrpn-Ube3a Imprinted Gene Loci and Their Involvement in Hereditary Disorders

Non-coding RNAs (ncRNAs) have long been recognized at imprinted gene loci and provided early paradigms to investigate their functions and molecular mechanisms of action. The characteristic feature of imprinted genes, their monoallelic, parental-origin-dependent expression, is achieved through complex epigenetic regulation, which is modulated by ncRNAs. This minireview focuses on two imprinted gene clusters, in which changes in ncRNA expression contribute to human disorders. At the GNAS locus loss of NESP RNA can cause autosomal dominant Pseudohypoparathyroidism type 1b (AD-PHP-Ib), while at the SNRPN-UBE3A locus a long ncRNA and processed snoRNAs play a role in Angelman-Syndrome (AS) and Prader–Willi-Syndrome (PWS). The ncRNAs silence overlapping protein-coding transcripts in sense or anti-sense orientation through changes in histone modifications as well as DNA methylation at CpG-rich sequence motifs. Their epigenetic modulatory functions are required in early development in the pre-implantation embryo or already in the parental germ cells. However, it remains unclear whether the sequence homology-carrying ncRNA itself is required, or whether the process of its transcription through other promoters causes the silencing effect.

Paternally inherited gsα mutation impairs adipogenesis and potentiates a lean phenotype in vivo

Paternally inherited inactivating mutations of the GNAS gene have been associated with a rare and disabling genetic disorder, progressive osseous heteroplasia, in which heterotopic ossification occurs within extraskeletal soft tissues, such as skin, subcutaneous fat, and skeletal muscle. This ectopic bone formation is hypothesized to be caused by dysregulated mesenchymal progenitor cell differentiation that affects a bipotential osteogenic-adipogenic lineage cell fate switch. Interestingly, patients with paternally inherited inactivating mutations of GNAS are uniformly lean. Using a mouse model of Gsα-specific exon 1 disruption, we examined whether heterozygous inactivation of Gnas affects adipogenic differentiation of mesenchymal precursor cells from subcutaneous adipose tissues (fat pad). We found that paternally inherited Gsα inactivation (Gsα(+/p-) ) impairs adipogenic differentiation of adipose-derived stromal cells (ASCs). The Gsα(+/p-) mutation in ASCs also decreased expression of the adipogenic factors CCAAT-enhancer-binding protein (C/EBP)β, C/EBPα, peroxisome proliferator-activated receptor gamma, and adipocyte protein 2. Impaired adipocyte differentiation was rescued by an adenylyl cyclase activator, forskolin, and provided evidence that Gsα-cAMP signals are necessary in early stages of this process. Supporting a role for Gnas in adipogenesis in vivo, fat tissue weight and expression of adipogenic genes from multiple types of adipose tissues from Gsα(+/p-) mice were significantly decreased. Interestingly, the inhibition of adipogenesis by paternally inherited Gsα mutation also enhances expression of the osteogenic factors, msh homeobox 2, runt-related transcription factor 2, and osteocalcin. These data support the hypothesis that Gsα plays a critical role in regulating the balance between fat and bone determination in soft tissues, a finding that has important implications for a wide variety of disorders of osteogenesis and adipogenesis.

GE-25-like immunoreactivity in the rat eye

This study aimed to investigate the presence and distribution of the chromogranin A-derived peptide GE-25 in the rat eye. The molecular form detected by the GE-25 antiserum was evaluated in the rat trigeminal ganglion, retina and remaining tissues of the rat eye by means of Western blots and the distribution pattern of GE-25-like immunoreactivity was studied in the rat eye and rat trigeminal ganglion by immunofluorescence. One single band of approximately 70kDa was stained in the trigeminal ganglion and retina which represents the uncleaved intact chromogranin A indicating that the proteolytic processing of chromogranin A to GE-25 is limited in these tissues. Sparse GE-25-like immunoreactive nerve fibers were visualized in the corneal stroma, at the limbus around blood vessels, in the sphincter and dilator muscle and stroma of the iris, in the stroma of the ciliary body and ciliary processes and in the stroma and around blood vessels in the choroid. This distribution pattern is characteristic for neuropeptides whereas the presence of immunoreactivity in the corneal endothelium and in Müller glia in the retina is atypical. GE-25-like immunoreactivity was found in small to medium-sized ganglion cells in the rat trigeminal ganglion clearly indicating that the nerve fibers in the rat eye are of sensory origin. The colocalization of GE-25-immunoreactivity with SP-immunoreactivity in the rat ciliary body is in agreement with the presumption of the sensory nature of the innervation of the anterior segment of the eye by GE-25.

Loss of XLαs (extra-large αs) imprinting results in early postnatal hypoglycemia and lethality in a mouse model of pseudohypoparathyroidism Ib

Maternal deletion of the NESP55 differentially methylated region (DMR) (delNESP55/ASdel3-4(m), delNAS(m)) from the GNAS locus in humans causes autosomal dominant pseudohypoparathyroidism type Ib (AD-PHP-Ib(delNASm)), a disorder of proximal tubular parathyroid hormone (PTH) resistance associated with loss of maternal GNAS methylation imprints. Mice carrying a similar, maternally inherited deletion of the Nesp55 DMR (ΔNesp55(m)) replicate these Gnas epigenetic abnormalities and show evidence for PTH resistance, yet these mice demonstrate 100% mortality during the early postnatal period. We investigated whether the loss of extralarge αs (XLαs) imprinting and the resultant biallelic expression of XLαs are responsible for the early postnatal lethality in ΔNesp55(m) mice. First, we found that ΔNesp55(m) mice are hypoglycemic and have reduced stomach-to-body weight ratio. We then generated mice having the same epigenetic abnormalities as the ΔNesp55(m) mice but with normalized XLαs expression due to the paternal disruption of the exon giving rise to this Gnas product. These mice (ΔNesp55(m)/Gnasxl(m+/p-)) showed nearly 100% survival up to postnatal day 10, and a substantial number of them lived to adulthood. The hypoglycemia and reduced stomach-to-body weight ratio observed in 2-d-old ΔNesp55(m) mice were rescued in the ΔNesp55(m)/Gnasxl(m+/p-) mice. Surviving double-mutant animals had significantly reduced Gαs mRNA levels and showed hypocalcemia, hyperphosphatemia, and elevated PTH levels, thus providing a viable model of human AD-PHP-Ib. Our findings show that the hypoglycemia and early postnatal lethality caused by the maternal deletion of the Nesp55 DMR result from biallelic XLαs expression. The double-mutant mice will help elucidate the pathophysiological mechanisms underlying AD-PHP-Ib.

The extended granin family: structure, function, and biomedical implications

The chromogranins (chromogranin A and chromogranin B), secretogranins (secretogranin II and secretogranin III), and additional related proteins (7B2, NESP55, proSAAS, and VGF) that together comprise the granin family subserve essential roles in the regulated secretory pathway that is responsible for controlled delivery of peptides, hormones, neurotransmitters, and growth factors. Here we review the structure and function of granins and granin-derived peptides and expansive new genetic evidence, including recent single-nucleotide polymorphism mapping, genomic sequence comparisons, and analysis of transgenic and knockout mice, which together support an important and evolutionarily conserved role for these proteins in large dense-core vesicle biogenesis and regulated secretion. Recent data further indicate that their processed peptides function prominently in metabolic and glucose homeostasis, emotional behavior, pain pathways, and blood pressure modulation, suggesting future utility of granins and granin-derived peptides as novel disease biomarkers.

Expression and imprinting analysis of the NESP55 gene in pigs

Most imprinted genes play important roles in a mammalian development. One of them is GNAS complex locus which codes for several imprinted or biallelically expressed transcripts. The function of some of them are well understood (for example GSα-guanine nucleotide binding, α -stimulating protein is essential element of cell signaling), whereas the others are little known. The function of NESP55 (Neuroendocrine secretory protein 55) remains elusive, although there are suggestions about its role in brain development. Imprinted genes are currently being studied as potential candidate genes for quantitative trait loci (QTLs) in farm animals. In our study, we analyzed tissue distribution of NESP55 mRNA in pigs and established imprinting status of this gene in the brain stem, muscle, kidney and liver at several developmental stages. NESP55 mRNA was most abundant in central nervous system (CNS) and pituitary. Substantial expression was also noticed in the kidney, testis and muscle. Moreover, we identified a 12-nucleotides deletion within the coding region of NESP55 (accession number ss#342570450) which was used in imprinting analysis. The deletion was very rare in the analyzed populations and present only in heterozygous form. The imprinting analysis showed that NESP55 is maternally expressed in young and adult pigs, similar to what was obtained in humans, mice and cattle.

Parathyroid hormone signaling via Gαs is selectively inhibited by an NH(2)-terminally truncated Gαs: implications for pseudohypoparathyroidism

Pseudohypoparathyroid patients have resistance predominantly to parathyroid hormone (PTH), and here we have examined the ability of an alternative Gαs-related protein to inhibit Gαs activity in a hormone-selective manner. We tested whether the GNAS exon A/B-derived NH(2)-terminally truncated (Tr) αs protein alters stimulation of adenylate cyclase by the PTH receptor (PTHR1), the thyroid-stimulating hormone (TSH) receptor (TSHR), the β(2)-adrenergic receptor (β(2)AR), or the AVP receptor (V2R). HEK293 cells cotransfected with receptor and full-length (FL) Gαs ± Tr αs protein expression vectors were stimulated with agonists (PTH [10(-7) to 10(-9)  M], TSH [1 to 100 mU], isoproterenol [10(-6) to 10(-8)  M], or AVP [10(-6) to 10(-8)  M]). Following PTH stimulation, HEK293 cells cotransfected with PTHR1 + FL Gαs + Tr αs had a significantly lower cAMP response than those transfected with only PTHR1 + FL Gαs. Tr αs also exerted an inhibitory effect on the cAMP levels stimulated by TSH via the TSHR but had little or no effect on isoproterenol or AVP acting via β(2)AR or V2R, respectively. These differences mimic the spectrum of hormone resistance in pseudohypoparathyroidism type 1a (PHP-1a) and type 1b (PHP-1b) patients. In opossum kidney (OK) cells, endogenously expressing the PTHR1 and β(2)AR, the exogenous expression of Tr αs at a level similar to endogenous FL Gαs resulted in blunting of the cAMP response to PTH, whereas that to isoproterenol was unaltered. A pseudopseudohypoparathyroid patient with Albright hereditary osteodystrophy harbored a de novo paternally inherited M1I Gαs mutation. Similar maternally inherited mutations at the initiation codon have been identified previously in PHP-1a patients. The M1I αs mutant (lacking the first 59 amino acids of Gαs) blunted the increase in cAMP levels stimulated via the PTHR1 in both HEK293 and OK cells similar to the Tr αs protein. Thus NH(2)-terminally truncated forms of Gαs may contribute to the pathogenesis of pseudohypoparathyroidism by inhibiting the activity of Gαs itself in a GPCR selective manner.

Immunohistochemical expression of neuroendocrine secretory protein-55 (NESP-55) in pituitary adenomas

Neuroendocrine secretory protein-55 (NESP-55) is a recently described member of the chromogranin family and appears to be a marker of the constitutive secretory pathway in certain neural, neuroendocrine, and endocrine cell types. It has been shown to be selectively expressed in tumors differentiating towards the adrenal chromaffin and pancreatic islet cell phenotypes. The highest levels of NESP-55 expression, at least in animals, appear to be in the adrenal medulla and the pituitary gland. However, very little is known about the status of NESP-55 expression in pituitary adenomas. We therefore studied the immunohistochemical profile of NESP-55 expression in a series of 30 well-characterized pituitary adenomas (five each of FSH/LH and ACTH, four GH, three TSH, seven prolactin, and six null cells). All tumors were positive for one or more generic marker(s) (chromogranin A, synaptophysin, neuron-specific enolase) of neuroendocrine differentiation. All pituitary adenomas selected for study were stained for NESP-55 with appropriate positive and negative controls. NESP-55 immunoreactivity, seen as brown finely granular cytoplasmic staining of the tumor cells with prominent perinuclear accentuation, was graded as focal (<10% tumor cells staining), moderate (10-50% tumor cells staining), and diffuse (>50% tumor cell staining). Four of seven prolactinomas were positive for NESP-55 (one focal, two moderate, and one diffuse). Two of four GH adenomas were also positive (one focal and one diffuse) while only 1/5 FSH tumors showed a moderately intense immunoreactivity. All other pituitary adenomas were completely negative for NESP-55. Our results indicate that, in human pituitary adenomas, NESP-55 has a more restricted pattern of expression than that of chromogranins A and B. Since immunohistochemical expression of NESP-55 is largely confined to prolactinomas and GH adenomas, it raises the possibility that NESP-55 may somehow be involved in the secretory pathways of these specific cell types.

The GNAS Locus: Quintessential Complex Gene Encoding Gsalpha, XLalphas, and other Imprinted Transcripts

The currently estimated number of genes in the human genome is much smaller than previously predicted. As an explanation for this disparity, most individual genes have multiple transcriptional units that represent a variety of biologically important gene products. GNAS exemplifies a gene of such complexity. One of its products is the alpha-subunit of the stimulatory heterotrimeric G protein (Gsalpha), a ubiquitous signaling protein essential for numerous different cellular responses. Loss-of-function and gain-of-function mutations within Gsalpha-coding GNAS exons are found in various human disorders, including Albright's hereditary osteodystrophy, pseudohypoparathyroidism, fibrous dysplasia of bone, and some tumors of different origin. While Gsalpha expression in most tissues is biallelic, paternal Gsalpha expression is silenced in a small number of tissues, playing an important role in the development of phenotypes associated with GNAS mutations. Additional products derived exclusively from the paternal GNAS allele include XLalphas, a protein partially identical to Gsalpha, and two non-coding RNA molecules, the A/B transcript and the antisense transcript. The maternal GNAS allele leads to NESP55, a chromogranin-like neuroendocrine secretory protein. In vivo animal models have demonstrated the importance of each of the exclusively imprinted GNAS products in normal mammalian physiology. However, although one or more of these products are also disrupted by most naturally occurring GNAS mutations, their roles in disease pathogenesis remain unknown. To further our understanding of the significance of this gene in physiology and pathophysiology, it will be important to elucidate the cellular roles and the mechanisms regulating the expression of each GNAS product.

Regulation of dorsal raphe nucleus function by serotonin autoreceptors: a behavioral perspective

Neurotransmission by serotonin (5-HT) is tightly regulated by several autoreceptors that fine-tune serotonergic neurotransmission through negative feedback inhibition at the cell bodies (predominantly 5-HT(1A)) or at the axon terminals (predominantly 5-HT(1B)); however, more subtle roles for 5-HT(1D) and 5-HT(2B) autoreceptors have also been detected. This review provides an overview of 5-HT autoreceptors, focusing on their contribution in animal behavioral models of stress and emotion. Experiments targeting 5-HT autoreceptors in awake, behaving animals have generally shown that increasing autoreceptor feedback is anxiolytic and rewarding, while enhanced 5-HT function is aversive and anxiogenic; however, the role of serotonergic activity in behavioral models of helplessness is more complex. The prevailing model suggests that 5-HT autoreceptors become desensitized in response to stress exposure and antidepressant administration, two seemingly opposite manipulations. Thus there are still unresolved questions regarding the role of these receptors-and serotonin in general-in normal and pathological states.

Potent constitutive cyclic AMP-generating activity of XLαs implicates this imprinted GNAS product in the pathogenesis of McCune-Albright syndrome and fibrous dysplasia of bone

Patients with McCune-Albright syndrome (MAS), characterized primarily by hyperpigmented skin lesions, precocious puberty, and fibrous dyslasia of bone, carry postzygotic heterozygous mutations of GNAS causing constitutive cAMP signaling. GNAS encodes the α-subunit of the stimulatory G protein (Gsα), as well as a large variant (XLαs) derived from the paternal allele. The mutations causing MAS affect both GNAS products, but whether XLαs, like Gsα, can be involved in the pathogenesis remains unknown. Here, we investigated biopsy samples from four previously reported and eight new patients with MAS. Activating mutations of GNAS (Arg201 with respect to the amino acid sequence of Gsα) were present in all the previously reported and five of the new cases. The mutation was detected within the paternally expressed XLαs transcript in five and the maternally expressed NESP55 transcript in four cases. Tissues carrying paternal mutations appeared to have higher XLαs mRNA levels than maternal mutations. The human XLαs mutant analogous to Gsα-R201H (XLαs-R543H) showed markedly higher basal cAMP accumulation than wild-type XLαs in transfected cells. Wild-type XLαs demonstrated higher basal and isoproterenol-induced cAMP signaling than Gsα and co-purified with Gβ1γ2 in transduced cells. XLαs mRNA was measurable in mouse calvarial cells, with its level being significantly higher in undifferentiated cells than those expressing preosteoblastic markers osterix and alkaline phosphatase. XLαs mRNA was also expressed in murine bone marrow stromal cells and preosteoblastic MC3T3-E1 cells. Our findings are consistent with the possibility that constitutive XLαs activity adds to the molecular pathogenesis of MAS and fibrous dysplasia of bone.

DNA sequence polymorphisms within the bovine guanine nucleotide-binding protein Gs subunit alpha (Gsα)-encoding (GNAS) genomic imprinting domain are associated with performance traits

BACKGROUND

Genes which are epigenetically regulated via genomic imprinting can be potential targets for artificial selection during animal breeding. Indeed, imprinted loci have been shown to underlie some important quantitative traits in domestic mammals, most notably muscle mass and fat deposition. In this candidate gene study, we have identified novel associations between six validated single nucleotide polymorphisms (SNPs) spanning a 97.6 kb region within the bovine guanine nucleotide-binding protein Gs subunit alpha gene (GNAS) domain on bovine chromosome 13 and genetic merit for a range of performance traits in 848 progeny-tested Holstein-Friesian sires. The mammalian GNAS domain consists of a number of reciprocally-imprinted, alternatively-spliced genes which can play a major role in growth, development and disease in mice and humans. Based on the current annotation of the bovine GNAS domain, four of the SNPs analysed (rs43101491, rs43101493, rs43101485 and rs43101486) were located upstream of the GNAS gene, while one SNP (rs41694646) was located in the second intron of the GNAS gene. The final SNP (rs41694656) was located in the first exon of transcripts encoding the putative bovine neuroendocrine-specific protein NESP55, resulting in an aspartic acid-to-asparagine amino acid substitution at amino acid position 192.

RESULTS

SNP genotype-phenotype association analyses indicate that the single intronic GNAS SNP (rs41694646) is associated (P ≤ 0.05) with a range of performance traits including milk yield, milk protein yield, the content of fat and protein in milk, culled cow carcass weight and progeny carcass conformation, measures of animal body size, direct calving difficulty (i.e. difficulty in calving due to the size of the calf) and gestation length. Association (P ≤ 0.01) with direct calving difficulty (i.e. due to calf size) and maternal calving difficulty (i.e. due to the maternal pelvic width size) was also observed at the rs43101491 SNP. Following adjustment for multiple-testing, significant association (q ≤ 0.05) remained between the rs41694646 SNP and four traits (animal stature, body depth, direct calving difficulty and milk yield) only. Notably, the single SNP in the bovine NESP55 gene (rs41694656) was associated (P ≤ 0.01) with somatic cell count--an often-cited indicator of resistance to mastitis and overall health status of the mammary system--and previous studies have demonstrated that the chromosomal region to where the GNAS domain maps underlies an important quantitative trait locus for this trait. This association, however, was not significant after adjustment for multiple testing. The three remaining SNPs assayed were not associated with any of the performance traits analysed in this study. Analysis of all pairwise linkage disequilibrium (r2) values suggests that most allele substitution effects for the assayed SNPs observed are independent. Finally, the polymorphic coding SNP in the putative bovine NESP55 gene was used to test the imprinting status of this gene across a range of foetal bovine tissues.

CONCLUSIONS

Previous studies in other mammalian species have shown that DNA sequence variation within the imprinted GNAS gene cluster contributes to several physiological and metabolic disorders, including obesity in humans and mice. Similarly, the results presented here indicate an important role for the imprinted GNAS cluster in underlying complex performance traits in cattle such as animal growth, calving, fertility and health. These findings suggest that GNAS domain-associated polymorphisms may serve as important genetic markers for future livestock breeding programs and support previous studies that candidate imprinted loci may act as molecular targets for the genetic improvement of agricultural populations. In addition, we present new evidence that the bovine NESP55 gene is epigenetically regulated as a maternally expressed imprinted gene in placental and intestinal tissues from 8-10 week old bovine foetuses.

Effects of deficiency of the G protein Gsα on energy and glucose homeostasis

G(s)α is a ubiquitously expressed G protein α-subunit that couples receptors to the generation of intracellular cyclic AMP. The G(s)α gene GNAS is a complex gene that undergoes genomic imprinting, an epigenetic phenomenon that leads to differential expression from the two parental alleles. G(s)α is imprinted in a tissue-specific manner, being expressed primarily from the maternal allele in a small number of tissues. Albright hereditary osteodystrophy is a monogenic obesity disorder caused by heterozygous G(s)α mutations but only when the mutations are maternally inherited. Studies in mice indicate a similar parent-of-origin effect on energy and glucose metabolism, with maternal but not paternal mutations leading to obesity, reduced sympathetic nerve activity and energy expenditure, glucose intolerance and insulin resistance, with no primary effect on food intake. These effects result from G(s)α imprinting leading to severe G(s)α deficiency in one or more regions of the central nervous system, and are associated with a specific defect in melanocortins to stimulate sympathetic nerve activity and energy expenditure.

Diseases associated with genomic imprinting

Genomic imprinting is the phenomenon where the expression of a locus differs between the maternally and paternally inherited alleles. Typically, this manifests as transcriptional silencing of one of the alleles, although many genes are imprinted in a tissue- or isoform-specific manner. Diseases associated with imprinted genes include various cancers, disorders of growth and metabolism, and disorders in neurodevelopment, cognition, and behavior, including certain major psychiatric disorders. In many cases, the disease phenotypes associated with dysfunction at particular imprinted loci can be understood in terms of the evolutionary processes responsible for the origin of imprinting. Imprinted gene expression represents the outcome of an intragenomic evolutionary conflict, where natural selection favors different expression strategies for maternally and paternally inherited alleles. This conflict is reasonably well understood in the context of the early growth effects of imprinted genes, where paternally inherited alleles are selected to place a greater demand on maternal resources than are maternally inherited alleles. Less well understood are the origins of imprinted gene expression in the brain, and their effects on cognition and behavior. This chapter reviews the genetic diseases that are associated with imprinted genes, framed in terms of the evolutionary pressures acting on gene expression at those loci. We begin by reviewing the phenomenon and evolutionary origins of genomic imprinting. We then discuss diseases that are associated with genetic or epigenetic defects at particular imprinted loci, many of which are associated with abnormalities in growth and/or feeding behaviors that can be understood in terms of the asymmetric pressures of natural selection on maternally and paternally inherited alleles. We next described the evidence for imprinted gene effects on adult cognition and behavior, and the possible role of imprinted genes in the etiology of certain major psychiatric disorders. Finally, we conclude with a discussion of how imprinting, and the evolutionary-genetic conflicts that underlie it, may enhance both the frequency and morbidity of certain types of diseases.

Skeletal progenitors and the GNAS gene: fibrous dysplasia of bone read through stem cells

Activating mutations of the GNAS gene, which causes fibrous dysplasia of bone (FD), lead to remarkable changes in the properties of skeletal progenitors, and it is these changes that mediate the pathological effect of this gene on bone. Mutated skeletal stem cells lose the ability to differentiate into adipocytes, and to maintain in situ, and transfer heterotopically, the hematopoietic microenvironment, leading to abnormal bone marrow histology in FD. They overexpress molecular effectors of osteoclastogenesis, thus promoting inappropriate bone resorption leading to fragility of FD bone. They express the phosphate-regulating hormone FGF-23 at normal levels, whose excess in the serum of FD patients correlates with the mass of osteogenic cells within FD lesions, leading to osteomalacia and deformity of the FD bone, and revealing that bone is an endocrine organ regulating renal handling of phosphate. Mechanisms of allelic selection and stem cell selection occur in mutated skeletal stem cells and contribute to the inherent diversity and evolution over time in FD. The definition of the etiological role of GNAS mutations marks the watershed between many decades of descriptive observation and the definition of cellular and molecular mechanisms that would explain and hopefully allow for a cure for the disease. Placing stem cells at center stage has permitted substantial advances in one decade, and promises more for the one to come.

Immunohistochemical and biochemical studies with region-specific antibodies to chromogranins A and B and secretogranins II and III in neuroendocrine tumors

This short review deals with our investigations in neuroendocrine tumors (NETs) with antibodies against defined epitopes of chromogranins (Cgs) A and B and secretogranins (Sgs) II and III. The immunohistochemical expression of different epitopes of the granin family of proteins varies in NE cells in normal human endocrine and non-endocrine organs and in NETs, suggesting post-translational processing. In most NETs one or more epitopes of the granins were lacking, but variations in the expression pattern occurred both in benign and malignant NETs. A few epitopes displayed patterns that may be valuable in differentiating between benign and malignant NET types, e.g., well-differentiated NET types expressed more CgA epitopes than the poorly differentiated ones and C-terminal secretoneurin visualized a cell type related to malignancy in pheochromocytomas. Plasma concentrations of different epitopes of CgA and CgB varied. In patients suffering from carcinoid tumors or endocrine pancreatic tumors the highest concentrations were found with epitopes from the mid-portion of CgA. For CgB the highest plasma concentrations were recorded for the epitope 439-451. Measurements of SgII showed that patients with endocrine pancreatic tumors had higher concentrations than patients with carcinoid tumors or pheochromocytomas. SgIII was not detectable in patients with NETs.

Imprinting status of Galpha(s), NESP55, and XLalphas in cell cultures derived from human embryonic germ cells: GNAS imprinting in human embryonic germ cells

GNAS is a complex gene that through use of alternative first exons encodes signaling proteins Galpha(s) and XLalphas plus neurosecretory protein NESP55. Tissue-specific expression of these proteins is regulated through reciprocal genomic imprinting in fully differentiated and developed tissue. Mutations in GNAS account for several human disorders, including McCune-Albright syndrome and Albright hereditary osteodystrophy, and further knowledge of GNAS imprinting may provide insights into variable phenotypes of these disorders. We therefore analyzed expression of Galpha(s), NESP55, and XLalphas prior to tissue differentiation in cell cultures derived from human primordia germ cells. We found that the expression of Galpha(s) was biallelic (maternal allele: 52.6%+/- 2.5%; paternal allele: 47.2%+/- 2.5%; p= 0.07), whereas NESP55 was expressed preferentially from the maternal allele (maternal allele: 81.9%+/- 10%; paternal allele: 18.1%+/- 10%; p= 0.002) and XLalphas was preferentially expressed from the paternal allele (maternal allele: 2.7%+/- 0.3%; paternal allele: 97.3%+/- 0.3%; p= 0.007). These results demonstrate that imprinting of NESP55 occurs very early in development, although complete imprinting appears to take place later than 5-11 weeks postfertilization, and that imprinting of XLalphas occurs very early postfertilization. By contrast, imprinting of Galpha(s) most likely occurs after 11 weeks postfertilization and after tissue differentiation.

Deletion of the noncoding GNAS antisense transcript causes pseudohypoparathyroidism type Ib and biparental defects of GNAS methylation in cis

CONTEXT

GNAS encodes the alpha-subunit of the stimulatory G protein as well as additional imprinted transcripts including the maternally expressed NESP55 and the paternally expressed XLalphas, antisense, and A/B transcripts. Most patients with pseudohypoparathyroidism type Ib (PHP-Ib) exhibit imprinting defects affecting the maternal GNAS allele, which are thought to reduce/abolish Gsalpha expression in renal proximal tubules and thereby cause resistance to PTH.

OBJECTIVE

Our objective was to define the genetic defect in a previously unreported family with autosomal dominant PHP-Ib.

DESIGN AND SETTING

Analyses of serum and urine chemistries and of genomic DNA and lymphoblastoid-derived RNA were conducted at a tertiary hospital and research laboratory.

PATIENTS

Affected individuals presented with muscle weakness and/or paresthesia and showed hypocalcemia, hyperphosphatemia, and elevated serum PTH. Obligate carriers were healthy and revealed no obvious abnormality in mineral ion homeostasis.

RESULTS

A novel 4.2-kb microdeletion was discovered in the affected individuals and the obligate carriers, ablating two noncoding GNAS antisense exons while preserving the NESP55 exon. On maternal transmission, the deletion causes loss of all maternal GNAS imprints, partial gain of NESP55 methylation, and PTH resistance. Paternal transmission of the mutation leads to epigenetic alterations in cis, including a partial loss of NESP55 methylation and a partial gain of A/B methylation.

CONCLUSIONS

The identified deletion points to a unique cis-acting element located telomeric of the NESP55 exon that is critical for imprinting both GNAS alleles. These findings provide novel insights into the molecular mechanisms underlying PHP and GNAS imprinting.

Granins and their derived peptides in normal and tumoral chromaffin tissue: Implications for the diagnosis and prognosis of pheochromocytoma

Pheochromocytomas are rare catecholamine-secreting tumors that arise from chromaffin tissue within the adrenal medulla and extra-adrenal sites. Typical clinical manifestations are sustained or paroxysmal hypertension, severe headaches, palpitations and sweating resulting from hormone excess. However, their presentation is highly variable and can mimic many other diseases. The diagnosis of pheochromocytomas depends mainly upon the demonstration of catecholamine excess by 24-h urinary catecholamines and metanephrines or plasma metanephrines. Occurrence of malignant pheochromocytomas can only be asserted by imaging of metastatic lesions, which are associated with a poor survival rate. The characterization of tissue, circulating or genetic markers is therefore crucial for the management of these tumors. Proteins of the granin family and their derived peptides are present in dense-core secretory vesicles and secreted into the bloodstream, making them useful markers for the identification of neuroendocrine cells and neoplasms. In this context, we will focus here on reviewing the distribution and characterization of granins and their processing products in normal and tumoral chromaffin cells, and their clinical usefulness for the diagnosis and prognosis of pheochromocytomas. It appears that, except SgIII, all members of the granin family i.e. CgA, CgB, SgII, SgIV-SgVII and proSAAS, and most of their derived peptides are present in adrenomedullary chromaffin cells and in pheochromocytes. Moreover, besides the routinely used CgA test assays, other assays have been developed to measure concentrations of tissue and/or circulating granins or their derived peptides in order to detect the occurrence of pheochromocytomas. In most cases, elevated levels of these entities were found, in correlation with tumor occurrence, while rarely discriminating between benign and malignant neoplasms. Nevertheless, measurement of the levels of granins and derived peptides improves the diagnostic sensitivity and may therefore provide a complementary tool for the management of pheochromocytomas. However, the existing data need to be substantiated in larger groups of patients, particularly in the case of malignant disease.

Gut hormones: emerging role in immune activation and inflammation

Gut inflammation is characterized by mucosal recruitment of activated cells from both the innate and adaptive immune systems. In addition to immune cells, inflammation in the gut is associated with an alteration in enteric endocrine cells and various biologically active compounds produced by these cells. Although the change in enteric endocrine cells or their products is considered to be important in regulating gut physiology (motility and secretion), it is not clear whether the change plays any role in immune activation and in the regulation of gut inflammation. Due to the strategic location of enteric endocrine cells in gut mucosa, these gut hormones may play an important role in immune activation and promotion of inflammation in the gut. This review addresses the research on the interface between immune and endocrine systems in gastrointestinal (GI) pathophysiology, specifically in the context of two major products of enteric endocrine systems, namely serotonin (5-hydroxytryptamine: 5-HT) and chromogranins (Cgs), in relation to immune activation and generation of inflammation. The studies reviewed in this paper demonstrate that 5-HT activates the immune cells to produce proinflammatory mediators and by manipulating the 5-HT system it is possible to modulate gut inflammation. In the case of Cgs the scenario is more complex, as this hormone has been shown to play both proinflammatory and anti-inflammatory functions. It is also possible that interaction between 5-HT and Cgs may play a role in the modulation of immune and inflammatory responses. In addition to enhancing our understanding of immunoendocrine interaction in the gut, the data generated from the these studies may have implications in understanding the role of gut hormone in the pathogenesis of both GI and non-GI inflammatory diseases which may lead ultimately to improved therapeutic strategies in inflammatory disorders.

Granins and granin-related peptides in neuroendocrine tumours

This review focus on neuroendocrine tumours (NETs), with special reference to the immunohistochemical analysis of granins and granin-related peptides and their usefulness in identifying and characterizing the great diversity of NET types. Granins, their derived peptides, and complex protein-processing enzyme systems that cleave granins and prohormones, have to some extent cell-specific expression patterns in normal and neoplastic NE cells. The marker most commonly used in routine histopathology to differentiate between non-NETs and NETs is chromogranin (Cg) A, to some extent CgB. Other members of the granin family may also be of diagnostic value by identifying special NET types, e.g. secretogranin (Sg) VI was only found in pancreatic NETs and phaeochromocytomas. SgIII has recently arisen as an important NET marker; it was strongly expressed in NETs, with some exceptions--phaeochromocytomas expressed few cells and parathyroid adenomas none. Some expression patterns of granin-related peptides seem valuable in differentiating between some benign and malignant NETs, some may also provide prognostic information, among which: well-differentiated NET types expressed more CgA epitopes than the poorly differentiated ones, except insulinomas, where the opposite was noted; medullary thyroid carcinomas containing few cells immunoreactive to a CgB antibody were related to a bad prognosis; C-terminal secretoneurin visualized a cell type related to malignancy in phaeochromocytomas. Further research will probably establish new staining patterns with marker functions for granins in NETs which may be of histopathological diagnostic value.

New insights into granin-derived peptides: evolution and endocrine roles

The granin protein family is composed of two chromogranin and five secretogranin members that are acidic, heat-stable proteins in secretory granules in cells of the nervous and endocrine systems. We report that there is little evidence for evolutionary relationships among the granins except for the chromogranin group. The main granin members, including chromogranin A and B, and secretogranin II are moderately conserved in the vertebrates. Several small bioactive peptides can be generated by proteolysis from those homologous domains existing within the granin precursors, reflecting the conservation of biological activities in different vertebrates. In this context, we focus on reviewing the distribution and function of the major granin-derived peptides, including vasostatin, bovine CgB(1-41) and secretoneurin in vertebrate endocrine systems, especially those associated with growth, glucose metabolism and reproduction.

The role of GNAS and other imprinted genes in the development of obesity

Genomic imprinting is an epigenetic phenomenon affecting a small number of genes, which leads to differential expression from the two parental alleles. Imprinted genes are known to regulate fetal growth and a 'kinship' or 'parental conflict' model predicts that paternally and maternally expressed imprinted genes promote and inhibit fetal growth, respectively. In this review we examine the role of imprinted genes in postnatal growth and metabolism, with an emphasis on the GNAS/Gnas locus. GNAS is a complex imprinted locus with multiple oppositely imprinted gene products, including the G-protein alpha-subunit G(s)alpha that is expressed primarily from the maternal allele in some tissues and the G(s)alpha isoform XLalphas that is expressed only from the paternal allele. Maternal, but not paternal, G(s)alpha mutations lead to obesity in Albright hereditary osteodystrophy. Mouse studies show that this phenomenon is due to G(s)alpha imprinting in the central nervous system leading to a specific defect in the ability of central melanocortins to stimulate sympathetic nervous system activity and energy expenditure. In contrast mutation of paternally expressed XLalphas leads to opposite metabolic effects in mice. Although these findings conform to the 'kinship' model, the effects of other imprinted genes on body weight regulation do not conform to this model.

Cloning and expression analysis of a murine novel gene, Ayu17-449

We used gene trapping vector PU8 to search some interesting genes which play important roles in mouse development from murine ES cells. One positive ES colony termed Ayu17-449 was trapped. Its partial cDNA was obtained by using 5' RACE method. It is homologous to a 5,523 bp cDNA fragment (GI: 20879412) in EST database. Further analysis of the 5,523 bp cDNA sequence in Celera mouse gene database showed that it overlaps two genes. We designed serials of DNA primers according to the mRNAs of these two genes for RT-PCR and Northern blotting analysis, and identified a novel RNA about 9 kb (we named it as Ayu17-449) encoding 1,920 aa. This gene is expressed highly in the brain, kidney, heart, lung, muscle and stomach. The expressed protein contains a Granin motif on its N-terminus, showing that this gene may be involved in hormone secretion.

Improved identification of endogenous peptides from murine nervous tissue by multiplexed peptide extraction methods and multiplexed mass spectrometric analysis

In recent years, mass spectrometry (MS) based techniques have made their entrance in the analysis of endogenous peptides extracted from nervous tissue. In this study, we introduce a novel peptide extraction procedure using 8 M urea, next to the more established extraction method that uses acetic acid. The extracted peptide mixtures are analyzed by both high-resolution nanoLC MS/MS using collision induced dissociation (CID) on an LTQ-Orbitrap and nanoLC electron transfer induced dissociation (ETD) on a linear ion trap. The combined use of the two extraction methods significantly increased the yield of identified endogenous neuropeptides. The multiplexed use of high mass accuracy mass spectrometry and the ETD fragmentation technique further increased the yield and confidence of peptide identifications. Furthermore, reduction of disulfide bridges during sample preparation was essential in the identification of several endogenous peptides containing cysteine disulfide bonds. Through this study, we identified in total 142 peptides in extracts of the mouse pituitary tissue, whereby 43 uniquely in the urea extract and 11 uniquely in the acetic acid extract. A large number of detected endogenous peptides were reported previously, but we confidently identified 22 unreported peptides that possess characteristics of endogenous peptides and are thus interesting targets to be explored further.

New mutation type in pseudohypoparathyroidism type Ia

CONTEXT

The GNAS gene encodes the alpha-subunit of the stimulatory G proteins, which play a crucial role in intracellular signal transduction of peptide and neurotransmitter receptors. Heterozygous inactivating maternally inherited mutations of GNAS (including translation initiation mutations, amino acid substitutions, nonsense mutations, splice site mutations and small insertions or deletions) lead to a phenotype in which Albright hereditary osteodystrophy is associated with pseudohypoparathyroidism type Ia.

OBJECTIVE

We sought to identify the molecular defect in a patient who was thought to have PHP-Ia.

METHODS AND RESULTS

The GNAS gene of a 5-year-old boy with brachydactily, mental retardation, pseudohypoparathyroidism and congenital hypothyroidism was investigated. We found a heterozygous inversion of exon 2 and part of intron 1 of de novo origin. Molecular studies of cDNA from blood RNA demonstrated that both the normal and the mutant variants were stable and that new splice-sites were generated.

CONCLUSION

This report demonstrates the first evidence for an inversion at the GNAS gene responsible of pseudohypoparathyroidism type Ia.

Genomic imprinting in the development and evolution of psychotic spectrum conditions

I review and evaluate genetic and genomic evidence salient to the hypothesis that the development and evolution of psychotic spectrum conditions have been mediated in part by alterations of imprinted genes expressed in the brain. Evidence from the genetics and genomics of schizophrenia, bipolar disorder, major depression, Prader-Willi syndrome, Klinefelter syndrome, and other neurogenetic conditions support the hypothesis that the etiologies of psychotic spectrum conditions commonly involve genetic and epigenetic imbalances in the effects of imprinted genes, with a bias towards increased relative effects from imprinted genes with maternal expression or other genes favouring maternal interests. By contrast, autistic spectrum conditions, including Kanner autism, Asperger syndrome, Rett syndrome, Turner syndrome, Angelman syndrome, and Beckwith-Wiedemann syndrome, commonly engender increased relative effects from paternally expressed imprinted genes, or reduced effects from genes favouring maternal interests. Imprinted-gene effects on the etiologies of autistic and psychotic spectrum conditions parallel the diametric effects of imprinted genes in placental and foetal development, in that psychotic spectrum conditions tend to be associated with undergrowth and relatively-slow brain development, whereas some autistic spectrum conditions involve brain and body overgrowth, especially in foetal development and early childhood. An important role for imprinted genes in the etiologies of psychotic and autistic spectrum conditions is consistent with neurodevelopmental models of these disorders, and with predictions from the conflict theory of genomic imprinting.

Peripheral projections of NESP55 containing neurons in the rat sympathetic ganglia

The peripheral projections of neurons expressing neuroendocrine secretory protein 55 (NESP55), a novel member of the chromogranin family, were studied by retrograde tracing technique. It was found that NESP55 positive neurons in the rat superior cervical ganglion projected to a number of targets including the submandibular gland, the cervical lymph nodes, the forehead skin, the iris, but not to the thyroid. Among these NESP55 positive target-projecting neurons, a subpopulation contained neuropeptide Y (NPY), a vasoconstrictor. Forepaw pad projecting neurons were found exclusively in the stellate ganglion, almost all of which (approximately 90%) were immunoreactive to NESP55. Colocalization of NESP55 and calcitonin gene-related peptide (CGRP), a peptide involved in sudomotor effects, was observed in a subpopulation of these paw pad projecting neurons, as was colocalization of NESP55 and NPY. The data suggest that NESP55 may have a functional role in some populations of sympathetic neurons.

Physiological Dysfunctions Associated with Mutations of the Imprinted Gnas Locus

The ubiquitous Gαs-subunit of the trimeric, stimulatory G-protein plays a central role in receptor-mediated signal transduction, coupling receptor activation with the production of cAMP. The Gαs-encoding locus Gnas is now known to consist of a complex arrangement of several protein-coding and noncoding transcripts. We provide an overview of its genomic organization, its regulation by genomic imprinting, and a summary of the physiological roles of the alternative protein variants Gαs and XLαs as determined from deficient mouse models.

PCR-based analysis of differentially methylated regions of GNAS enables convenient diagnostic testing of pseudohypoparathyroidism type Ib

BACKGROUND

Pseudohypoparathyroidism type Ib (PHPIb) is characterized by parathyroid hormone (PTH) resistance, which can lead to hypocalcemia, hyperphosphatemia, and increased serum PTH. The disorder is caused by mutations in regulatory regions of the GNAS gene (GNAS complex locus) that lead to interferences in the methylation status of alternative GNAS promoters, such as exon A/B, NESP55, and XL alpha-s. PHPIb comprises disorders that show distinctive changes in methylation status but share the same clinical phenotype: (a) loss of methylation only at exon A/B of the GNAS gene and involving no other obvious epigenetic abnormalities [e.g., those caused by heterozygous microdeletions in the STX16 (syntaxin 16) region and found in many patients with autosomal dominant (AD) PHPIb]; (b) methylation abnormalities at several differentially methylated regions (DMRs), which are observed in most patients with sporadic PHPIb and some families with AD PHPIb.

METHODS

To permit early and reliable diagnosis of suspected PHPIb, we designed methylation-sensitive restriction enzyme-based and bisulfite deamination-based PCR tests for exon A/B and NESP55 DMRs.

RESULTS

Both PCR strategies permit proper methylation testing of GNAS and NESP55 DMRs and elucidate different disease subtypes. We have identified a novel microsatellite repeat polymorphism within GNAS exon A/B, and pedigree analyses have shown its presence to be conclusive evidence for familial disease.

CONCLUSIONS

We provide a simple diagnostic test for PHPIb, an imprinting disorder caused by different molecular changes within the GNAS complex locus. PHPIb, a complex and diagnostically challenging clinical phenotype, can be treated successfully by taking steps before the manifestation of symptoms to avoid clinical complications in affected patients or asymptomatic members of affected families who show positive results in genetic tests.

A maternal epimutation of GNAS leads to Albright osteodystrophy and parathyroid hormone resistance

CONTEXT

Pseudohypoparathyroidism (PHP) type Ia is a rare maternally transmitted disease due to maternal loss-of-function mutations of GNAS, the gene encoding Galphas, the alpha-stimulatory subunit of the G protein. Affected individuals display hormonal resistance (mainly PTH and TSH resistance) and Albright hereditary osteodystrophy. PHP type Ib (PHP-Ib), usually defined by isolated renal resistance to PTH and sometimes mild TSH resistance, is due to a maternal loss of GNAS exon A/B methylation, leading to decreased Galphas expression in specific tissues.

OBJECTIVE AND RESULTS

We report a girl with obvious Albright osteodystrophy features, PTH resistance, normal Galphas bioactivity in red blood cells, yet no loss-of-function mutation in the GNAS coding sequence (exons 1-13). The methylation analysis of the four GNAS differentially methylated regions, i.e. NESP, AS, XL, and A/B, revealed broad methylation changes at all differentially methylated regions, including GNAS exon A/B, leading to a paternal epigenotype on both alleles.

CONCLUSIONS

This observation suggests that: 1) the decreased expression of Galphas due to GNAS epimutations is not restricted to the renal tubule but may affect nonimprinted tissues like bone; 2) PHP-Ib is a heterogeneous disorder that should lead to studying GNAS epigenotype in patients with PHP and no mutation in GNAS exons 1-13, regardless of their physical features.