Zona glomerulosa-specific factor: cloning and function

Disruption of the mouse Jhy gene causes abnormal ciliary microtubule patterning and juvenile hydrocephalus

Congenital hydrocephalus, the accumulation of excess cerebrospinal fluid (CSF) in the ventricles of the brain, affects one of every 1000 children born today, making it one of the most common human developmental disorders. Genetic causes of hydrocephalus are poorly understood in humans, but animal models suggest a broad genetic program underlying the regulation of CSF balance. In this study, the random integration of a transgene into the mouse genome led to the development of an early onset and rapidly progressive hydrocephalus. Juvenile hydrocephalus transgenic mice (Jhy(lacZ)) inherit communicating hydrocephalus in an autosomal recessive fashion with dilation of the lateral ventricles observed as early as postnatal day 1.5. Ventricular dilation increases in severity over time, becoming fatal at 4-8 weeks of age. The ependymal cilia lining the lateral ventricles are morphologically abnormal and reduced in number in Jhy(lacZ/lacZ) brains, and ultrastructural analysis revealed disorganization of the expected 9+2 microtubule pattern. Rather, the majority of Jhy(lacZ/lacZ) cilia develop axonemes with 9+0 or 8+2 microtubule structures. Disruption of an unstudied gene, 4931429I11Rik (now named Jhy) appears to underlie the hydrocephalus of Jhy(lacZ/lacZ) mice, and the Jhy transcript and protein are decreased in Jhy(lacZ/lacZ) mice. Partial phenotypic rescue was achieved in Jhy(lacZ/lacZ) mice by the introduction of a bacterial artificial chromosome (BAC) carrying 60-70% of the JHY protein coding sequence. Jhy is evolutionarily conserved from humans to basal vertebrates, but the predicted JHY protein lacks identifiable functional domains. Ongoing studies are directed at uncovering the physiological function of JHY and its role in CSF homeostasis.

Adrenocortical stem and progenitor cells: implications for adrenocortical carcinoma

The continuous centripetal repopulation of the adrenal cortex is consistent with a population of cells endowed with the stem/progenitor cell properties of self-renewal and pluripotency. The adrenocortical capsule and underlying undifferentiated cortical cells are emerging as critical components of the stem/progenitor cell niche. Recent genetic analysis has identified various signaling pathways including Sonic Hedgehog (Shh) and Wnt as crucial mediators of adrenocortical lineage and organ homeostasis. Shh expression is restricted to the peripheral cortical cells that express a paucity of steroidogenic genes but give rise to the underlying differentiated cells of the cortex. Wnt/β-catenin signaling maintains the undifferentiated state and adrenal fate of adrenocortical stem/progenitor cells, in part through induction of its target genes Dax1 and inhibin-α, respectively. The pathogenesis of ACC, a rare yet highly aggressive cancer with an extremely poor prognosis, is slowly emerging from studies of the stem/progenitor cells of the adrenal cortex coupled with the genetics of familial syndromes in which ACC occurs. The frequent observation of constitutive activation of Wnt signaling due to loss-of-function mutations in the tumor suppressor gene APC or gain-of-function mutation in β-catenin in both adenomas and carcinomas, suggests perhaps that the Wnt pathway serves an early or initiating insult in the oncogenic process. Loss of p53 might be predicted to cooperate with additional genetic insults such as IGF2 as both are the most common genetic abnormalities in malignant versus benign adrenocortical neoplasms. It is unclear whether other factors such as Pod1 and Pref1, which are implicated in stem/progenitor cell biology in the adrenal and/or other organs, are also implicated in the etiology of adrenocortical carcinoma. The rarity and heterogeneous presentation of ACC makes it difficult to identify the cellular origin and the molecular progression to cancer. A more complete understanding of adrenocortical stem/progenitor cell biology will invariably aid in characterization of the molecular details of ACC tumorigenesis and may offer new options for therapeutic intervention.

The spatial and temporal expression of delta-like protein 1 in the rat pituitary gland during development

An analysis of secreted proteins by the signal sequence trap method using a cDNA library of the rat pituitary anlage at embryonic days (E) 13.5 revealed the abundant expression of delta-like protein 1 (Dlk1) in the pituitary gland. Dlk1, an epidermal growth factor-like repeat protein in preadipocytes, functions in maintaining the preadipose state. Expression of Dlk1 mRNA in the pituitary at E13.5 and in the adult pituitary was confirmed by in situ hybridization. The expression pattern of Dlk1 during pituitary development was also studied by immunohistochemistry. Dlk1 protein first appeared in Rathke's pouch and the infundibulum at E11.5; as development proceeded, expression became restricted to the pars distalis and pars tuberalis (PT). Dlk1 was expressed in most ACTH cells during the embryonic stages, but its expression was limited to only a few ACTH cells in the adult pituitary. It was also expressed in a small population of TSH, GTH, and PRL cells throughout development, whereas it was present in the cytoplasm of most GH cells at all developmental stages. Similarly, Dlk1 was localized in the cytoplasm of PT cells during development. These findings provide new insights into the mechanism of Dlk1 regarding its regulation of pituitary hormone-secreting cells during development.

Invalidation of TASK1 potassium channels disrupts adrenal gland zonation and mineralocorticoid homeostasis

TASK1 (KCNK3) and TASK3 (KCNK9) are two-pore domain potassium channels highly expressed in adrenal glands. TASK1/TASK3 heterodimers are believed to contribute to the background conductance whose inhibition by angiotensin II stimulates aldosterone secretion. We used task1-/- mice to analyze the role of this channel in adrenal gland function. Task1-/- exhibited severe hyperaldosteronism independent of salt intake, hypokalemia, and arterial 'low-renin' hypertension. The hyperaldosteronism was fully remediable by glucocorticoids. The aldosterone phenotype was caused by an adrenocortical zonation defect. Aldosterone synthase was absent in the outer cortex normally corresponding to the zona glomerulosa, but abundant in the reticulo-fasciculata zone. The impaired mineralocorticoid homeostasis and zonation were independent of the sex in young mice, but were restricted to females in adults. Patch-clamp experiments on adrenal cells suggest that task3 and other K+ channels compensate for the task1 absence. Adrenal zonation appears as a dynamic process that even can take place in adulthood. The striking changes in the adrenocortical architecture in task1-/- mice are the first demonstration of the causative role of a potassium channel in development/differentiation.

Regulation of growth hormone expression by Delta-like protein 1 (Dlk1)

Delta-like protein 1 (Dlk1) is a transmembrane protein characterized by epidermal growth factor (EGF)-like repeats. Dlk1, which is also known as preadipocyte factor 1 (pref-1) because of its ability to inhibit preadipocyte differentiation, regulates the differentiation of several other cell types through unknown mechanisms. To elucidate Dlk1 functions, identification of Dlk1-regulated target genes is critical. The observation that Dlk1 is expressed in many endocrine tissues suggests that Dlk1 may have endocrine-related functions. Because Dlk1 is expressed in GH producing cells, we hypothesize that one function of Dlk1 is to regulate GH expression. We found that GH mRNA, protein, and secretion were significantly decreased in GH3 pituitary cell clones that stably express Dlk1. In contrast, Dlk1 expression was unable to alter prolactin expression. Co-transfection of GH3 cells with a GH promoter-regulated reporter gene showed that Dlk1 repressed GH promoter activity. Deletion and mutation analysis of the GH promoter indicated that Pit-1 binding sites in the GH promoter are required for Dlk1-mediated repression. Furthermore, Dlk1 expression represses Pit-1-mediated transcription when both proteins are co-expressed in MCF-7 cells. Deletion analysis of Dlk1 revealed that the ability of Dlk1 to regulate GH promoter activity is independent of both its EGF-like repeats and its ability to modulate MAP kinase activity. The observation that Dlk1 regulates GH expression identifies the first endocrine function of Dlk1, establishes GH as a Dlk1-regulated target gene, and provides a model system to facilitate studies of Dlk1-mediated signaling.

Allele-specific histone modifications regulate expression of the Dlk1-Gtl2 imprinted domain

Dlk1 and Gtl2 are reciprocally expressed imprinted genes located on mouse chromosome 12. The Dlk1-Gtl2 locus carries three differentially methylated regions (DMRs), which are methylated only on the paternal allele. Of these, the intergenic (IG) DMR, located 12 kb upstream of Gtl2, is required for proper imprinting of linked genes on the maternal chromosome, while the Gtl2 DMR, located across the promoter of the Gtl2 gene, is implicated in imprinting on both parental chromosomes. In addition to DNA methylation, modification of histone proteins is also an important regulator of imprinted gene expression. Chromatin immunoprecipitation was therefore used to examine the pattern of histone modifications across the IG and Gtl2 DMRs. The data show maternal-specific histone acetylation at the Gtl2 DMR, but not at the IG DMR. In contrast, only low levels of histone methylation were observed throughout the region, and there was no difference between the two parental alleles. An existing mouse line carrying a deletion/insertion upstream of Gtl2 is unable to imprint the Dlk1-Gtl2 locus properly and demonstrates loss of allele-specific methylation at the Gtl2 DMR. Further analysis of these animals now shows that the loss of allele-specific methylation is accompanied by increased paternal histone acetylation at the Gtl2 DMR, with the activated paternal allele adopting a maternal acetylation pattern. These data indicate that interactions between DNA methylation and histone acetylation are involved in regulating the imprinting of the Dlk1-Gtl2 locus.

Microarray analysis of blood microvessels from PDGF-B and PDGF-Rbeta mutant mice identifies novel markers for brain pericytes

Normal blood microvessels are lined by pericytes, which contribute to microvessel development and stability through mechanisms that are poorly understood. Pericyte deficiency has been implicated in the pathogenesis of microvascular abnormalities associated with diabetes and tumors. However, the unambiguous identification of pericytes is still a problem because of cellular heterogeneity and few available molecular markers. Here we describe an approach to identify pericyte markers based on transcription profiling of pericyte-deficient brain microvessels isolated from platelet-derived growth factor (PDGF-B)-/- and PDGF beta receptor (PDGFRbeta)-/- mouse mutants. The approach was validated by the identification of known pericyte markers among the most down-regulated genes in PDGF-B-/- and PDGFRbeta-/- microvessels. Of candidates for novel pericyte markers, we selected ATP-sensitive potassium-channel Kir6.1 (also known as Kcnj8) and sulfonylurea receptor 2, (SUR2, also known as Abcc9), both part of the same channel complex, as well as delta homologue 1 (DLK1) for in situ hybridization, which demonstrated their specific expression in brain pericytes of mouse embryos. We also show that Kir6.1 is highly expressed in pericytes in brain but undetectable in pericytes in skin and heart. The three new brain pericyte markers are signaling molecules implicated in ion transport and intercellular signaling, potentially opening new windows on pericyte function in brain microvessels.

Dlk1 expression marks developing endothelium and sites of branching morphogenesis in the mouse embryo and placenta

The protein product of the Delta-like 1 (Dlk1) gene belongs to the Delta-Notch family of signaling molecules, proteins involved in cell fate determination in many tissues during development. The DLK1 protein is believed to function as a growth factor, maintaining the proliferative state of undifferentiated cells, and is usually down-regulated as immature cells differentiate. The expression pattern of the DLK1 protein has been described in certain human tissues; however, Dlk1 expression is not well understood in the mouse, the most tractable mammalian genetic model system. To better understand the role of Dlk1 in embryonic development, the tissue-specific expression pattern of Dlk1 mRNA during mouse embryogenesis was analyzed by in situ hybridization. In embryonic day 12.5 (e12.5) embryos, high levels of Dlk1 were found in the developing pituitary, pancreas, lung, adrenal, and many mesodermally derived tissues. Strikingly, Dlk1 expression also marks the growing branches of organs that develop through the process of branching morphogenesis. At e16.5, Dlk1 expression is down-regulated in most tissues but remains in the pituitary, the adrenal gland, and in skeletal muscle. In the placenta, expression of Dlk1 is detected in endothelial cells lining the fetal blood vessels of the labyrinth. This pattern is distinct from that seen in the human placenta and suggests a role for Dlk1 in regulating maternal-fetal interactions.

Leydig cells of the human testis possess astrocyte and oligodendrocyte marker molecules

It has been established, that Leydig cells of the human testis possess neuroendocrine properties and are therefore a member of the diffuse neuroendocrine (paraneuron) system. In the present study, we examined whether Leydig cells of adult (51-86 year of age) and developing (between the 15th and 36th week of gestation) human testes are immunopositive for glial cell-specific antigens such as glial fibrillary acidic protein (GFAP), galactocerebroside (GalC), cyclic 2',3'-nucleotide-3'-phosphodiesterase (CNPase), A2B5-antigen (A2B5) and O4-antigen (O4). With the use of Western blots and dot blot analyses, respectively, GFAP, CNPase, GalC, A2B5 and O4 were found in whole testes and Leydig cell protein extracts of adult men. Corresponding immunohistochemical studies revealed presence of these antigens in the cytoplasm of Leydig cells both of adult testes and testes during prenatal development. Some differences in staining intensity of single antigens were observed probably depending on the functional and/or developmental stage of the single cells. In addition, GFAP-, GalC- and CNPase-immunopositivity was found in numerous Sertoli cells of the seminiferous tubules. Moreover, some connective tissue cells (compartmentalizing cells or Co-cells) of the intertubular space showed immunopositivity for CNPase, A2B5 and GalC. The results obtained show that Leydig cells of the human testis, in addition to their endocrine, neuronal and neuroendocrine features, possess qualities of both astrocytes and oligodendrocytes and thus show qualities of multipotential cells. Leydig cells probably differentiate to a phenotype that is characteristic for cells in the developing nervous system. Furthermore, the established immunohistochemical similarities are consistent with the assumption that foetal and postnatal Leydig cells are of common origin.

Neurons in the monoaminergic nuclei of the rat and human central nervous system express FA1/dlk

The gene DLK1 encodes a member of the epidermal growth factor (EGF) superfamily, delta-like (dlk). When exposed in vivo to the action of an unknown protease, this type 1 membrane protein generates a soluble peptide referred to as Fetal antigen 1 (FA1). By acting in juxtacrine as well as paracrine/autocrine manners, both forms have been shown to be active in the differentiation/proliferation process of various cell types. In adults, FA1/dlk has been demonstrated mainly within (neuro) endocrine tissues. In this study we investigated the presence of FA1/dlk in other parts of the developing and adult rat and human CNS. Using immunocytochemistry and in situ hybridization we found that in both species FA1/dlk was expressed in neurons of the Edinger-Westphal's nucleus as well as in substantia nigra, ventral tegmental area (VTA), locus coeruleus and in certain parts of the raphe nuclei.

Fetal antigen 1 in healthy adults and patients with pituitary disease: relation to physiological, pathological, and pharmacological GH levels

Immunohistochemical analysis of the distribution of human fetal antigen 1 (FA1) in adult human tissues has demonstrated a strong association between FA1 and (neuro)endocrine structures. In the anterior pituitary gland FA1 was colocalized with GH, and the present study was performed to evaluate a possible relationship between GH and FA1. FA1 and GH levels were measured during a 24-h period at 20-min intervals. In contrast to the known GH peaks during 24-h sampling, there was no detectable FA1 peak. The FA1 responses to placebo were not significantly different from the responses to the combination of pyridostigmine and GHRH. No significant difference was found between basal FA1 (nanograms per ml) levels [median (minimum-maximum)] in healthy adults [n = 40; 28.6 ng/ml (12.5-72.0)], acromegalic patients [n = 11; 31.0 ng/ml (21.6-56.3)], and patients with GH deficiency [n = 22; 32.1 ng/ml (13.4-108.7)]. FA1 levels were significantly reduced, in the six of seven acromegalic GH responders to octreotide, from [median (minimum-maximum)] 30.6 ng/ml (20.0-43.1) to 20.3 (13.9-30.2; P < 0.02). There was no significant change during placebo. FA1 levels were significantly increased compared with placebo values during 3 months of GH therapy. The increase in FA1 levels was significantly higher than the change during placebo (P < 0.003). In conclusion, a common secretory and stimulatory pathway for FA1 and GH in healthy adults has been ruled out. However, we found that pharmacologically induced changes in GH levels during weeks to months had a corresponding direct or indirect effect on FA1 levels in patients with GH deficiency or acromegaly. However, a direct effect of octreotide on FA1 levels, independent of GH levels, has not been ruled out.

Does fetal antigen 1 (FA1) identify cells with regenerative, endocrine and neuroendocrine potentials? A study of FA1 in embryonic, fetal, and placental tissue and in maternal circulation

Fetal antigen 1 (FA1) is a circulating EGF multidomain glycoprotein. FA1 and its membrane-associated precursor is defined by the mRNAs referred to as delta-like (dlk), preadipocyte factor 1 (pref-1) or zona glomerulosa-specific factor (ZOG). Using a polyclonal antibody recognising both forms, the localisation of FA1/dlk was analysed in embryonic and fetal tissues between week 5 to 25 of gestation and related to germinal origin and development. FA1 was observed in endodermally derived hepatocytes, glandular cells of the pancreas anlage, and in respiratory epithelial cells. FA1 was also present in mesodermally derived cells of the renal proximal tubules, adrenal cortex, Leydig and Hilus cells of the testes and ovaries, fetal chondroblasts, and skeletal myotubes. Ectodermally derived neuro- and adenohypophysial cells, cells in the floor of the 3rd ventricle and plexus choroideus were also FA1 positive. The number of cells expressing FA1 decreased during fetal development where the expression became restricted to specific functional cells. Epidermis, gut epithelium, gall bladder, blood cells, spleen, thyroid gland, salivary glands, and smooth muscle cells were FA1 negative. Analysis of extra-embryonic tissues from normal and pathological pregnancies revealed FA1 in stromal cells surrounding the blood islands of the yolk sac as well as in placental fibroblasts where the expression was most pronounced in diploid, androgenic complete hydatidiform moles. However, as measured by ELISA, the circulating maternal FA1 levels in complete moles were not different from normal pregnancies. The results presented suggest that FA1 is a growth and/or differentiation factor extensively expressed in immature cells and down-regulated during fetal development. FA1 down-regulation was associated with a shift in the subcellular localisation indicating differential post-translational/post-transcriptional modifications during fetal development. FA1 may be a new marker of cellular subtypes with a regenerative potential and of specific cells with endocrine or neuroendocrine functions.

Altered expression of androgen-receptor isoforms in human colon-cancer tissues

Many groups have examined of androgen the effects on normal and neoplastic colon tissues, but no clear picture has hitherto emerged. In particular, the presence and the function of the androgen receptor (AR) has only partially been investigated in the past. The present study reports analysis of expression of the AR gene as messenger RNA and as protein in surgical samples of neoplastic colon mucosa and of corresponding healthy surrounding tissue. Specific binding for DHT, demonstrating the presence of AR, was observed in almost all the samples (2 samples out of 12 were negative). No significant difference was observed between healthy and neoplastic mucosa, or between male and female patients. A further characterization of AR was performed with Western blot, using 2 different primary antibodies. Both AR isoforms, AR-B and AR-A, were detected in healthy mucosa, while only AR-A, resolving at 87 kDa, was observed in neoplastic mucosa. RT-PCR analysis revealed the transcript for AR in both healthy and neoplastic mucosa in 10 samples; no message was detectable in 2 samples (negative also for binding); 2 additional samples presented AR mRNA only in healthy colon mucosa, 2 others only in neoplastic mucosa. In addition, a variant AR messenger RNA, probabily derived from alternative splicing, was observed. We found that AR is expressed both in healthy and in neoplastic colon mucosa, either as mRNA or as protein. Neoplastic colon tissue shows a characteristic loss of expression of the AR-B isoform, while AR-A expression is maintained. These findings underscore the possible role of androgen and its receptor in colon carcinogenesis.

General overview of mineralocorticoid hormone action

The adrenal cortex elaborates two major groups of steroids that have been arbitrarily classified as glucocorticoids and mineralocorticoids, despite the fact that carbohydrate metabolism is intimately linked to mineral balance in mammals. In fact, glucocorticoids assured both of these functions in all living cells, animal and photosynthetic, prior to the appearance of aldosterone in teleosts at the dawn of terrestrial colonization. The evolutionary drive for a hormone specifically designed for hydromineral regulation led to zonation for the conversion of 18-hydroxycorticosterone into aldosterone through the catalytic action of a synthase in the secluded compartment of the adrenal zona glomerulosa. Corticoid hormones exert their physiological action by binding to receptors that belong to a transcription factor superfamily, which also includes some of the proteins regulating steroid synthesis. Steroids stimulate sodium absorption by the activation and/or de novo synthesis of the ion-gated, amiloride-sensitive sodium channel in the apical membrane and that of the Na+/K+-ATPase in the basolateral membrane. Receptors, channels, and pumps apparently are linked to the cytoskeleton and are further regulated variously by methylation, phosphorylation, ubiquination, and glycosylation, suggesting a complex system of control at multiple checkpoints. Mutations in genes for many of these different proteins have been described and are known to cause clinical disease.

Cloning of a novel kinase (SIK) of the SNF1/AMPK family from high salt diet-treated rat adrenal

PCR-coupled cDNA subtraction hybridization was adapted to identify the genes expressed in the adrenocortical tissues from high salt diet-treated rat. A novel cDNA clone, termed salt-inducible kinase (SIK), encoding a polypeptide (776 amino acids) with significant similarity to protein serine/ threonine kinases in the SNF1/AMPK family was isolated. An in vitro kinase assay demonstrated that SIK protein had autophosphorylation activity. Northern blot revealed that SIK mRNA levels were markedly augmented by ACTH treatment both in rat adrenal glands and in Y1 cells. SIK may play an important role in the regulation of adrenocortical functions in response to high plasma salt and ACTH stimulation.

Pref-1, SF-1 and adrenocortical zonation

The stimulation of the zona glomerulosa phenotype by a low sodium diet is characterised by increased expression of aldosterone synthase accompanied by increases in (pro)renin, bFGF, c-fos and c-jun gene transcription. In contrast ACTH diminishes the specific glomerulosa phenotype. The EGF related transmembrane protein preadipocyte factor 1 (Pref-1) is specifically found in the zona glomerulosa and medulla of the adult rat adrenal as well as being expressed in fetal tissue. In addition the orphan nuclear receptor SF-1/Ad4bp considered to be an important factor in fetal adrenocortical development and differentiation may also have a role in zonal differentiation in the adult. To investigate their roles, adrenals were taken from adult Wistar rats maintained on a low sodium diet or ACTH treated (enhancing or diminishing zona glomerulosa function respectively) and compared with untreated controls. Localisation of Pref-1 was carried out by immunocytochemistry using the polyclonal antibody ZOG (anti Pref-1) and of SF-1 using a rabbit antiserum to SF-1. The experimental treatment resulted in a decrease and increase in Pref-1 expression in ACTH treated and low sodium diet treated rats respectively, in accordance with changes in abundance of glomerulosa cells. SF-1 expression was expected throughout the adrenal cortex, without zonal differentiation, though somewhat decreased by ACTH treatment. Of these two factors, only Pref-1 can be considered to have a role in zonal differentiation.

Implication of ZOG protein (zona glomerulosa-specific protein) in zone development of the adrenal cortex

The three zones of adrenal cortex are thought to arise from a single multipotential stem cell. Immunohistochemical studies of fetal and adult adrenals using an antibody against a previously-cloned ZOG protein, a rat homolog of Pref-1, were conducted to explore its roles in the differentiation of cortical tissues. At the early embryonic stage, ZOG was already expressed in adrenogonadal primordial cells. The ZOG-positive cells gradually formed the adrenal primordium by E14.5. By E17.5 the expression was repressed in the inner part of the aggregate and these cells began to express CYP11B1. The ZOG-positive cells at this stage existed at the periphery of the aggregate but they did not express CYP11B2 yet. Not until E20.5 did the aldosteronogenic cells appear among the ZOG-positive cells at the outermost part of the gland. Based on these and the other findings the zonal development of the adrenal cortex is discussed.