FA1 immunoreactivity in endocrine tumours and during development of the human fetal pancreas; negative correlation with glucagon expression

Soluble delta-like 1 homolog (DLK1) stimulates angiogenesis through Notch1/Akt/eNOS signaling in endothelial cells

AIM

Delta-like 1 homolog (DLK1) is a non-canonical ligand of Notch signaling, which plays a pivotal role in vascular development and tumor angiogenesis. This study aimed to elucidate the function and mechanism of DLK1 in angiogenesis.

METHODS AND RESULTS

By using in situ hybridization and immunohistochemical studies, expression analysis revealed a unique vascular tropism of DLK1 in vasculature of neuroblastoma and vascular tumors. Thus, it was hypothesized that DLK1 may be cleaved and then bound to endothelial cells, thereby regulating the endothelial function. To test such hypothesis, soluble DLK1 encompassing DLK1 extracellular domain (DLK1-EC) was generated and validated by its inhibitory function in adipogenesis assay. Recombinant DLK1-EC exhibited the preferential binding capability toward endothelial cells and stimulated the microvessels sprouting in aorta rings. Above all, implantation of DLK1-EC dose-dependently elicited the cornea neovascularization in rats. By using various angiogenesis assays, it was delineated that DLK1-EC stimulated the angiogenesis by promoting the proliferation, motility and tube formation of endothelial cells. By immunoblot and luciferase analysis, it was elucidated that DLK1-EC enhanced the expression and activities of Notch1/Akt/eNOS/Hes-1 signaling in dose- and time-dependent manners. Pharmaceutical blockage of Notch signaling using γ-secretase inhibitor DAPT abrogated the DLK1-EC-induced endothelial migration and Hes-1-driven luciferase activities. Furthermore, Notch1 inactivation by neutralizing antibodies or RNA interference reversed the DLK1-EC-induced angiogenesis.

CONCLUSIONS

The present study unveils the pro-angiogenic function and mechanism of soluble DLK1 through activation of Notch1 signaling in endothelial cells.

Cellular and molecular mechanisms underlying oxygen-dependent radiosensitivity

Molecular oxygen has long been recognized as a powerful radiosensitizer that enhances the cell-killing efficiency of ionizing radiation. Radiosensitization by oxygen occurs at very low concentrations with the half-maximum radiosensitization at approximately 3 mmHg. However, robust hypoxia-induced signal transduction can be induced at <15 mmHg and can elicit a wide range of cellular responses that will affect therapy response as well as malignant progression. Great strides have been made, especially since the 1990s, toward identification and characterization of the oxygen-regulated molecular pathways that affect tumor response to ionizing radiation. In this review, we will discuss the current advances in our understanding of oxygen-dependent molecular modification and cellular signal transduction and their impact on tumor response to therapy. We will specifically address mechanistic distinctions between radiobiological hypoxia (0-3 mmHg) and pathological hypoxia (3-15 mmHg). We also propose a paradigm that hypoxia increases radioresistance by maintaining the cancer stem cell phenotype.

Overexpression of Pref-1 in pancreatic islet β-cells in mice causes hyperinsulinemia with increased islet mass and insulin secretion

Preadipocyte factor-1 (Pref-1) is made as a transmembrane protein containing EGF-repeats at the extracellular domain that can be cleaved to generate a biologically active soluble form. Pref-1 is found in islet β-cells and its level has been reported to increase in neonatal rat islets upon growth hormone treatment. We found here that Pref-1 can promote growth of pancreatic tumor derived AR42J cells. To examine Pref-1 function in pancreatic islets in vivo, we generated transgenic mouse lines overexpressing the Pref-1/hFc in islet β-cells using rat insulin II promoter (RIP). These transgenic mice exhibit an increase in islet mass with higher proportion of larger islets in pancreas compared to wild-type littermates. This is in contrast to pancreas from Pref-1 null mice that show higher proportion of smaller islets. Insulin expression and insulin secretion from pancreatic islets from RIP-Pref-1/hFc transgenic mice are increased also. Thus, RIP-Pref-1/hFc transgenic mice show normal glucose levels but with higher plasma insulin levels in both fasting and fed conditions. These mice show improved glucose tolerance. Taken together, we conclude Pref-1 as a positive regulator of islet β-cells and insulin production.

Segregation of neuronal and neuroendocrine differentiation in the sympathoadrenal lineage

Neuronal and neuroendocrine cells possess the capacity for Ca(2+)-regulated discharge of messenger molecules, which they release into synapses or the blood stream, respectively. The neural-crest-derived sympathoadrenal lineage gives rise to the sympathetic neurons of the autonomic nervous system and the neuroendocrine chromaffin cells of the adrenal medulla. These cells provide an excellent model system for studying common and distinct developmental mechanisms underlying the acquisition of neuroendocrine and neuronal properties. As catecholaminergic cells, they possess common markers related to noradrenaline synthesis, storage and release, but they also display diverging gene expression patterns and are morphologically and functionally different. The precise mechanisms that underlie the diversification of sympathoadrenal cells into neurons and neuroendocrine cells are not fully understood. However, in the past we could show that the establishment of a chromaffin phenotype does not depend on signals from the adrenal cortex and that chromaffin cells and sympathetic neurons apparently differ from the onset of their catecholaminergic differentiation. Nevertheless, the cues that specifically induce neuroendocrine features remain elusive. The early development of the progenitors of chromaffin cells and sympathetic neurons depends on a common set of transcription factors with overlapping but distinct influences on their development. In addition to the well-defined role of transcription factors as developmental regulators, our understanding of post-transcriptional gene regulation by microRNAs has substantially increased within the last few decades. This review highlights the major similarities and differences between chromaffin cells and sympathetic neurons, summarizes our current knowledge of the roles of selected transcription factors, microRNAs and environmental signals for the neuroendocrine differentiation of sympathoadrenal cells, and draws comparisons with the development of other endocrine and neuronal cells.

The Missing lnc(RNA) between the pancreatic β-cell and diabetes

Diabetes mellitus represents a group of complex metabolic diseases that result in impaired glucose homeostasis, which includes destruction of β-cells or the failure of these insulin-secreting cells to compensate for increased metabolic demand. Despite a strong interest in characterizing the transcriptome of the different human islet cell types to understand the molecular basis of diabetes, very little attention has been paid to the role of long non-coding RNAs (lncRNAs) and their contribution to this disease. Here we summarize the growing evidence for the potential role of these lncRNAs in β-cell function and dysregulation in diabetes, with a focus on imprinted genomic loci.

Functional characteristics of neonatal rat β cells with distinct markers

Neonatal β cells are considered developmentally immature and hence less glucose responsive. To study the acquisition of mature glucose responsiveness, we compared glucose-regulated redox state, insulin synthesis, and secretion of β cells purified from neonatal or 10-week-old rats with their transcriptomes and proteomes measured by oligonucleotide and LC-MS/MS profiling. Lower glucose responsiveness of neonatal β cells was explained by two distinct properties: higher activity at low glucose and lower activity at high glucose. Basal hyperactivity was associated with higher NAD(P)H, a higher fraction of neonatal β cells actively incorporating (3)H-tyrosine, and persistently increased insulin secretion below 5 mM glucose. Neonatal β cells lacked the steep glucose-responsive NAD(P)H rise between 5 and 10 mM glucose characteristic for adult β cells and accumulated less NAD(P)H at high glucose. They had twofold lower expression of malate/aspartate-NADH shuttle and most glycolytic enzymes. Genome-wide profiling situated neonatal β cells at a developmental crossroad: they showed advanced endocrine differentiation when specifically analyzed for their mRNA/protein level of classical neuroendocrine markers. On the other hand, discrete neonatal β cell subpopulations still expressed mRNAs/proteins typical for developing/proliferating tissues. One example, delta-like 1 homolog (DLK1) was used to investigate whether neonatal β cells with basal hyperactivity corresponded to a more immature subset with high DLK1, but no association was found. In conclusion, the current study supports the importance of glycolytic NADH-shuttling in stimulus function coupling, presents basal hyperactivity as novel property of neonatal β cells, and provides potential markers to recognize intercellular developmental differences in the endocrine pancreas.

Hypoxia and regulation of cancer cell stemness

Spontaneous tumors often contain heterogeneous populations of tumor cells with different tumor-initiating potentials or cancer cell "stemness." Clonal heterogeneity can be traced to specific locations inside a tumor where clones with different metastatic capabilities are identified, suggesting that the tumor microenvironment can exert a significant effect on the evolution of different clonal populations. Hypoxia is a common feature of tumor microenvironments and has the potential to facilitate malignant progression. This chapter provides a synopsis of hypoxia-regulated pathways implicated in the maintenance of cancer stem cells.

Interaction of delta-like 1 homolog (Drosophila) with prohibitins and its impact on tumor cell clonogenicity

Cancer stem cell characteristics, especially their self-renewal and clonogenic potentials, play an essential role in malignant progression and response to anticancer therapies. Currently, it remains largely unknown what pathways are involved in the regulation of cancer cell stemness and differentiation. Previously, we found that delta-like 1 homolog (Drosophila) or DLK1, a developmentally regulated gene, plays a critical role in the regulation of differentiation, self-renewal, and tumorigenic growth of neuroblastoma cells. Here, we show that DLK1 specifically interacts with the prohibitin 1 (PHB1) and PHB2, two closely related genes with pleiotropic functions, including regulation of mitochondrial function and gene transcription. DLK1 interacts with the PHB1-PHB2 complex via its cytoplasmic domain and regulates mitochondrial functions, including mitochondrial membrane potential and production of reactive oxygen species. We have further found that PHB1 and especially PHB2 regulate cancer cell self-renewal as well as their clonogenic potential. Hence, the DLK1-PHB interaction constitutes a new signaling pathway that maintains clonogenicity and self-renewal potential of cancer cells.

IMPLICATIONS

This study provides a new mechanistic insight into the regulation of the stem cell characteristics of cancer cells.

Effect of β-carotene on cancer cell stemness and differentiation in SK-N-BE(2)C neuroblastoma cells

Neuroblastoma is a solid tumor often diagnosed in childhood. While there have been intense efforts to develop a treatment for neuroblastoma, current therapies remain unsuccessful due to high rate of resistance and metastasis. Most cancers originate from a subset of self-renewing cells, primarily cancer stem cells (CSCs), which establish a tumor through continuous self-renewal and differentiation. The successful elimination of CSCs is an important goal in the development of effective strategies to achieve complete remission for cancers. Although β-carotene has been associated with several anticancer mechanisms, the efficacy of β-carotene against CSCs remains unclear. In the present study, β-carotene was shown to reduce cell growth and induce neuronal cell differentiation, concomitant with a marked increase in the phosphorylation of extracellular signal-regulated kinases (ERK) (p42/p44). More importantly, β-carotene inhibited self-renewal characteristics of CSCs and decreased expression of several stem cell markers. Levels of mRNA and protein of Drosophila delta-like 1 homolog (Drosophila) (DLK1) were downregulated following treatment with β-carotene. In addition, knockdown of DLK1 by siRNA enhanced the inhibitory effect of β-carotene on colony formation of neuroblastoma cells. β-carotene also potentiated the effect of cisplatin on the self-renewal characteristics of CSCs in neuroblastoma, revealing that β-carotene has the capacity to resensitize cells to cisplatin cytotoxicity by directly targeting CSCs. In conclusion, β-carotene was shown to strongly increase the anticancer efficacy against neuroblastoma cancer stem-like cells. Moreover, these results suggest that the targeting of CSCs is a novel mechanism of β-carotene. Thus, β-carotene is a potential chemotherapeutic reagent for this cancer.

Pituitary phenotypes of mice lacking the notch signalling ligand delta-like 1 homologue

The Notch signalling pathway ligand delta-like 1 homologue (Dlk1, also named Pref1) is expressed throughout the developing pituitary and becomes restricted to mostly growth hormone (GH) cells within the adult gland. We have investigated the role of Dlk1 in pituitary development and function from late embryogenesis to adulthood using a mouse model completely lacking the expression of Dlk1. We confirm that Dlk1-null mice are shorter and weigh less than wild-type littermates from late gestation, at parturition and in adulthood. A loss of Dlk1 leads to significant reduction in GH content throughout life, whereas other pituitary hormones are reduced to varying degrees depending on sex and age. Both the size of the pituitary and the proportion of hormone-producing cell populations are unchanged, suggesting that there is a reduction in hormone content per cell. In vivo challenge of mutant and wild-type littermates with growth hormone-releasing hormone and growth hormone-releasing hexapeptide shows that reduced GH secretion is unlikely to account for the reduced growth of Dlk1 knockout animals. These data suggest that loss of Dlk1 gives rise to minor pituitary defects manifesting as an age- and sex-dependent reduction in pituitary hormone contents. However, Dlk1 expression in other tissue is most likely responsible for the weight and length differences observed in mutant animals.

DLK1 Protein Expression during Mouse Development Provides New Insights into Its Function

Delta-like 1 homolog (DLK1) is a noncanonical ligand in the Delta-Notch signalling pathway. Although Dlk1 mRNA is abundantly present embryonically and declines rapidly just before birth, Dlk1 knockouts display a relatively mild phenotype. To assess whether this mild phenotype was due to posttranscriptional regulation, we studied the expression of DLK1 protein in mouse embryos and found abundant expression in liver, lung, muscle, vertebrae, pancreas, pituitary, and adrenal gland(s). DLK1 expression was absent in heart, stomach, intestine, kidney, epidermis, and central nervous system. DLK1 protein expression, therefore, correlates well with the reported Dlk1 mRNA expression pattern, which shows that its expression is mainly regulated at the pretranslational level. The comparison of the reported expression patterns of Notch mRNA and those of DLK1 in organs where lineage commitment and branching morphogenesis are important developmental processes suggests that DLK1 is a ligand that prevents premature Notch-dependent differentiation, possibly by competing with canonical ligands.

Conditional deletions refine the embryonic requirement for Dlk1

Numerous studies have implicated Delta-like 1 (DLK1), a transmembrane protein that shares homology with Notch ligands, in embryonic growth and differentiation. Dlk1 expression is widespread, though not ubiquitous, during early development, but is confined to a few specific cell types in adults. Adult Dlk1-expressing tissues include the Insulin-producing β-cells of the pancreas and the Growth hormone-producing somatotrophs of the pituitary gland. Previously generated Dlk1 null mice (Dlk1(Sul-pat)), display a partially penetrant neonatal lethality and a complex pattern of developmental and adult phenotypes. Here we describe the generation of a conditional Dlk1 mouse line (Dlk1(flox)) to facilitate cell type-specific deletion of the Dlk1 gene, providing a powerful system to explore each aspect of the Dlk1 null phenotype. Four tissue-specific Cre mouse lines were used to produce individual Dlk1 deletions in pancreatic β-cells, pituitary somatotrophs and the endothelial cells of the embryo and placenta, key candidates for the Dlk1 phenotype. Contrary to expectations, all of these conditional mice were fully viable, and none recapitulated any aspect of the Dlk1(Sul-pat) null mice. Dlk1 expression is therefore not essential for the normal development of β-cells, somatotrophs and endothelial cells, and the tissues responsible for the Dlk1 null phenotype remain to be identified. Dlk1(flox) mice will continue to provide an important tool for further research into the function of Dlk1.

Mulberry leaf extract inhibits cancer cell stemness in neuroblastoma

Emerging evidence proposes that most cancers originate from a rare subpopulation of cells, called cancer stem cells (CSCs), which possess characteristics including differentiation, self-renewal, and tumorigenicity. Currently, available therapeutic agents cannot effectively eliminate CSCs. Therefore, the development of a nontoxic, natural treatment that can either overcome chemoresistance or promote the elimination of CSCs is highly desirable. The current study examined whether mulberry leaf (ML) ethanolic extract can effectively eliminate neuroblastoma stem cell-like population. Our data demonstrated that 10-40 μg/ml of ML extract significantly enhanced differentiation by elongating neurites and reducing clonogenicity and sphere formation as shown by the decreased expression of stem cell markers and increased expression of differentiation markers. The knock-down of delta-like 1 homologue by siRNA enhanced the significant inhibitory effects of 40 μg/ml of ML extract on colony formation. Furthermore, phosphorylation of the extracellular signal-regulated kinase (ERK) was increased by 20 or 40 μg/ml of ML extract and the MEK/ERK inhibitors completely blocked differentiation induced by the extract. Taken together, these findings provide experimental evidence that ML may have chemopreventive effects on neuroblastoma cells by inhibiting CSCs characteristics as well as regulating CSCs pathways, which may provide a therapeutic option for controlling the growth of neuroblastoma cells.

Localizing transcriptional regulatory elements at the mouse Dlk1 locus

Much effort has focused recently on determining the mechanisms that control the allele-specific expression of genes subject to genomic imprinting, yet imprinting regulation is only one aspect of configuring appropriate expression of these genes. Imprinting control mechanisms must interact with those regulating the tissue-specific expression pattern of each imprinted gene in a cluster. Proper expression of the imprinted Delta-like 1 (Dlk1)-Maternally expressed gene 3 (Meg3) gene pair is required for normal fetal development in mammals, yet the mechanisms that control tissue-specific expression of these genes are unknown. We have used a combination of in vivo and in vitro expression assays to localize cis-regulatory elements that may regulate Dlk1 expression in the mouse embryo. A bacterial artificial chromosome transgene encompassing the Dlk1 gene and 77 kb of flanking sequence conferred expression in most endogenous Dlk1-expressing tissues. In combination with previous transgenic data, these experiments localize the majority of Dlk1 cis-regulatory elements to a 41 kb region upstream of the gene. Cross-species sequence conservation was used to further define potential regulatory elements, several of which functioned as enhancers in a luciferase expression assay. Two of these elements were able to drive expression of a lacZ reporter transgene in Dlk1-expressing tissues in the mouse embryo. The sequence proximal to Dlk1 therefore contains at least two discrete regions that may regulate tissue-specificity of Dlk1 expression.

DLK1, delta-like 1 homolog (Drosophila), regulates tumor cell differentiation in vivo

The stem cell-like characteristics of tumor cells are not only essential for tumor development and malignant progression, but also significantly contribute to therapy resistance. However, it remains poorly understood how cancer cell differentiation or stemness is regulated in vivo. We investigated the role of the stem cell gene DLK1, or delta-like 1 homolog (Drosophila), in the regulation of cancer cell differentiation in vivo using neuroblastoma (NB) xenografts as a model. We found that loss-of-function mutants of DLK1 significantly enhanced NB cell differentiation in vivo likely by increasing the basal phosphorylation of MEK and ERK kinases, a mechanism that has been shown to facilitate neuronal differentiation. We also found that DLK1(+) cells are preferentially located in hypoxic regions. These results clearly demonstrate that DLK1 plays an important role in the maintenance of undifferentiated, stem cell-like phenotypes of NB cells in vivo.

Effect of retinoic acid and delta-like 1 homologue (DLK1) on differentiation in neuroblastoma

The principal objective of this study was to evaluate the chemopreventive and therapeutic effects of a combination of all-trans-retinoic acid (RA) and knockdown of delta-like 1 homologue (Drosophila) (DLK1) on neuroblastoma, the most common malignant disease in children. As unfavorable neuroblastoma is poorly differentiated, neuroblastoma cell was induced differentiation by RA or DLK1 knockdown. Neuroblastoma cells showed elongated neurite growth, a hallmark of neuronal differentiation at various doses of RA, as well as by DLK1 knockdown. In order to determine whether or not a combination of RA and DLK1 knockdown exerts a greater chemotherapeutic effect on neuroblastoma, cells were incubated at 10 nM RA after being transfected with SiRNA-DLK1. Neuronal differentiation was increased more by a combination of RA and DLK1 knockdown than by single treatment. Additionally, in order to assess the signal pathway of neuroblastoma differentiation induced by RA and DLK1 knockdown, treatment with the specific MEK/ERK inhibitors, U0126 and PD 98059, was applied to differentiated neuroblastoma cells. Differentiation induced by RA and DLK1 knockdown increased ERK phosphorylation. The MEK/ERK inhibitor U0126 completely inhibited neuronal differentiation induced by both RA and DLK1 knockdown, whereas PD98059 partially blocked neuronal differentiation. After the withdrawal of inhibitors, cellular differentiation was fully recovered. This study is, to the best of our knowledge, the first to demonstrate that the specific inhibitors of the MEK/ERK pathway, U0126 and PD98059, exert differential effects on the ERK phosphorylation induced by RA or DLK1 knockdown. Based on the observations of this study, it can be concluded that a combination of RA and DLK1 knockdown increases neuronal differentiation for the control of the malignant growth of human neuroblastomas, and also that both MEK1 and MEK2 are required for the differentiation induced by RA and DLK1 knockdown.

Impact of the hypoxic tumor microenvironment on the regulation of cancer stem cell characteristics

Solid tumors often contain regions with insufficient oxygen delivery, a condition called hypoxia. Tumor hypoxia is an independent prognostic factor significantly correlated with advanced stages of malignancy, increased resistance to conventional therapy, and reduced disease-free survival. Hypoxic tumor cells exhibit poorly differentiated phenotypes resembling stem or progenitor cells. Studies have shown that hypoxia can inhibit tumor cell differentiation and promote maintenance of cancer stem cells. In addition, hypoxia also blocks the differentiation of mesenchymal stem/progenitor cells, a potential source of tumor-associated stromal cells. Therefore, hypoxia may play a critical role during the evolution of the tumor stromal microenvironment and formation of the putative cancer stem cell niches. Conceptually, hypoxia may help create a microenvironment enriched both in poorly differentiated tumor cells and in undifferentiated stromal cells. Such an undifferentiated hypoxic microenvironment may provide essential cellular interactions and environmental signals for the preferential maintenance of cancer stem cells. This review will discuss the hypoxia-regulated stem cell pathways and their roles in the maintenance of cancer stem cell functions.

Hypoxia-regulated delta-like 1 homologue enhances cancer cell stemness and tumorigenicity

Reduced oxygenation, or hypoxia, inhibits differentiation and facilitates stem cell maintenance. Hypoxia commonly occurs in solid tumors and promotes malignant progression. Hypoxic tumors are aggressive and exhibit stem cell-like characteristics. It remains unclear, however, whether and how hypoxia regulates cancer cell differentiation and maintains cancer cell stemness. Here, we show that hypoxia increases the expression of the stem cell gene DLK1, or delta-like 1 homologue (Drosophila), in neuronal tumor cells. Inhibition of DLK1 enhances spontaneous differentiation, decreases clonogenicity, and reduces in vivo tumor growth. Overexpression of DLK1 inhibits differentiation and enhances tumorigenic potentials. We further show that the DLK1 cytoplasmic domain, especially Tyrosine339 and Serine355, is required for maintaining both clonogenicity and tumorigenicity. Because elevated DLK1 expression is found in many tumor types, our observations suggest that hypoxia and DLK1 may constitute an important stem cell pathway for the regulation of cancer stem cell-like functionality and tumorigenicity.

The imprinted DLK1-MEG3 gene region on chromosome 14q32.2 alters susceptibility to type 1 diabetes

Genome-wide association (GWA) studies to map common disease susceptibility loci have been hugely successful, with over 300 reproducibly associated loci reported to date. However, these studies have not yet provided convincing evidence for any susceptibility locus subject to parent-of-origin effects. Using imputation to extend existing GWA datasets, we have obtained robust evidence at rs941576 for paternally inherited risk of type 1 diabetes (T1D; ratio of allelic effects for paternal versus maternal transmissions = 0.75; 95% confidence interval (CI) = 0.71-0.79). This marker is in the imprinted region of chromosome 14q32.2, which contains the functional candidate gene DLK1. Our meta-analysis also provided support at genome-wide significance for a T1D locus at chromosome 19p13.2. The highest association was at marker rs2304256 (odds ratio (OR) = 0.86; 95%CI = 0.82-0.90) in the TYK2 gene, which has previously been associated with systemic lupus erythematosus and multiple sclerosis.

Pref-1 and adipokine expression in adipose tissues of GK and Zucker rats

In view of the central role of preadipocyte factor-1, adiponectin and leptin in white adipose tissue function, the aim of the present study was to analyze the mRNA expression of these proteins and of the inflammatory markers interleukin-6 and tumor necrosis factor-alpha in visceral and subcutaneous fat pads of rats with different metabolic disorders. We demonstrated highly divergent expression of preadipocyte factor-1, upregulated expression of adiponectin, interleukin-6 and TNF-alpha mRNA in adipose tissues of the diabetic Goto Kakizaki rat compared to the obese Zucker rat. This was correlated to an increased number of large adipocytes and serum levels of adiponectin. Furthermore, in all four strains studied (as above plus Wistar Furth and Zucker Lean), significant heterogeneity was evident in adipokine expression within specific adipose tissues previously defined as belonging to the visceral or subcutaneous fat depots. These results suggest that significantly increased levels of inflammation and redistribution of adipocyte size are mechanisms contributing to the development of type 2 diabetes in the GK rat.

A role for notch signaling in stromal survival and differentiation during prostate development

Notch1 signaling is involved in epithelial growth and differentiation of prostate epithelia, and we have examined the role that notch signaling plays in the stroma of the developing prostate. We initially observed expression of delta-like 1 (Dlk1) and Notch2 in gene profiling studies of prostatic mesenchyme, and anticipated that they might be expressed in a key subset of inductive mesenchyme. Using quantitative RT-PCR, Northern blotting, and whole mount in situ hybridization, we confirmed that both Dlk1 and Notch2 mRNAs showed a restricted expression pattern within subsets of the stroma during prostate development. Localization of Dlk1 and Notch2 proteins mirrored the transcript expression, and showed both distinct and overlapping expression patterns within the stroma. Dlk1 and Notch2 were coexpressed in condensed inductive mesenchyme of the ventral mesenchymal pad (VMP), and were partially colocalized in the smooth muscle (SM) layer of the urethral stroma. In addition, Dlk1 was not expressed in SM adjacent to the VMP in female urethra. The function of notch signaling was examined using organ cultures of prostate rudiments and a small molecule inhibitor of notch receptor activity. Inhibition of notch signaling led to a loss of stromal tissue in both prostate and female VMP cultures, suggesting that this pathway was required for stromal survival. Inhibition of notch signaling also led to changes in both epithelial and stromal differentiation, which was evident in altered distributions of SM alpha-actin and p63 in prostates grown in vitro. The effects of notch signaling upon the stroma were only evident in the presence of testosterone, in contrast to effects upon epithelial differentiation.

The serum levels of the EGF-like homeotic protein dlk1 correlate with different metabolic parameters in two hormonally different children populations in Spain

BACKGROUND

The Dlk1 gene encodes for dlk1, a transmembrane protein belonging to the EGF-like repeat-containing family. Dlk1 has been shown to act as a regulator of adipogenesis. Fc-dlk1 transgenic mice show a decrease in adipose tissue and glucose tolerance, hypertriglyceridaemia and lower insulin sensitivity. Dlk1-deficient mice show growth retardation, increased serum lipid metabolites and develop obesity. These data advocate for a role of dlk1 in the maintenance of lipid homeostasis, and suggest that dlk1 levels may influence the development of cardiovascular disease.

AIM AND METHODS

In this study, we analysed whether dlk1 serum levels could be indicative of the different hormonal or metabolic status shown by two Spanish children populations (6-8 years-old), Orense and Murcia. We determined dlk1 serum levels by ELISA assay, using an antibody raised against the recombinant protein, and performed a correlation analysis against measurements of several hormonal and biochemical parameters in samples from 494 subjects.

RESULTS

We found a statistically significant positive correlation between serum levels of dlk1 and those of glucose (P < 0.05), total cholesterol (P < 0.01) and high-density lipoprotein-cholesterol (HDL-C) (P < 0.01) in children from Murcia, but not from Orense's population, where dehydroepiandrosterone-sulphate (DHEA-S) levels were significantly higher (P < 0.01) and dlk1 correlated positively with insulin (P < 0.01), homeostasis model assessment (HOMA) (P < 0.01) and free fatty acids (FFA) (P < 0.05).

CONCLUSIONS

dlk1 serum levels appear related to the anabolic status of the children in association with changes in the levels of DHEA-S, which have been associated with hyperinsulinaemia and diabetes. Monitoring dlk1 levels may be important to evaluate the metabolic and hormonal stage of child development.

Disabled-2 is expressed in adrenal zona glomerulosa and is involved in aldosterone secretion

The differentiation of the adrenal cortex into functionally specific zones is probably due to differential temporal gene expression during fetal growth, development, and adulthood. In our search for adrenal zona glomerulosa-specific genes, we found that Disabled-2 (Dab2) is expressed in the zona glomerulosa of the rat adrenal gland using a combination of laser capture microdissection, mRNA amplification, cDNA microarray hybridization, and real-time RT-PCR. Dab2 is an alternative spliced mitogen-regulated phosphoprotein with features of an adaptor protein and functions in signal transduction, endocytosis, and tissue morphogenesis during embryonic development. We performed further studies to analyze adrenal Dab2 localization, regulation, and role in aldosterone secretion. We found that Dab2 is expressed in the zona glomerulosa and zona intermedia of the rat adrenal cortex. Low-salt diet treatment increased Dab2-long isoform expression at the mRNA and protein level in the rat adrenal gland, whereas high-salt diet treatment did not cause any significant modification. Angiotensin II infusion caused a transient increase in both Dab2 isoform mRNAs in the rat adrenal gland. Dab2 overexpression in H295R human adrenocortical cells caused an increase in aldosterone synthase expression and up-regulated aldosterone secretion under angiotensin II-stimulated conditions. In conclusion, Dab2 is an adrenal gland zona glomerulosa- and intermedia-expressed gene that is regulated by aldosterone secretagogues such as low-salt diet or angiotensin II and is involved in aldosterone synthase expression and aldosterone secretion. Dab2 may therefore be a modulator of aldosterone secretion and be involved in mineralocorticoid secretion abnormalities.

The EGF-like Protein dlk1 Inhibits Notch Signaling and Potentiates Adipogenesis of Mesenchymal Cells

The EGF-like homeotic gene Dlk1 appears to function as an inhibitor of adipogenesis. Overexpression of Dlk1 prevents adipogenesis of 3T3-L1 cells. Dlk1-deficient mice are obese; however, adipose tissue still develops in Fc-dlk1 transgenic mice, suggesting that Dlk1 is not a strict inhibitor of adipogenesis. To clarify the role of Dlk1 in adipogenesis, we studied whether Dlk1 could act differently on this process depending upon the differentiation state of the precursor cells. We found that Dlk1 is a potentiator of adipogenesis for mesenchymal C3H10T1/2 cells. This potentiating effect can be triggered by overexpressing the entire protein or the extracellular EGF-like-containing region, but not by overexpressing the intracellular dlk1 sequence. In addition, coculture of C3H10T1/2 cells with other cells expressing Dlk1, but not with cells lacking Dlk1 expression, enhances their adipogenic response. Potentiation of adipogenesis by Dlk1 was associated with changes in the activation of ERK1/2 after IGFI/insulin induction. Finally, as reported with other cells, dlk1 functioned as a Notch signaling inhibitor in C3H10T1/2 cells, but inhibition of Notch1 expression prevented the potentiating effects of Dlk1 in adipogenesis. These data suggest that Dlk1 may potentiate or inhibit adipogenesis depending upon the cellular context, and that Notch1 expression and activation are important factors in this context.

The Novel Gene EGFL9/Dlk2, Highly Homologous to Dlk1, Functions as a Modulator of Adipogenesis

The Dlk1 gene appears to function as a regulator of adipogenesis. Adult Dlk1-deficient mice are obese, but adipose tissue still develops in transgenic mice overexpressing an Fc-dlk1 fusion protein, and neither type of genetically modified mice displays serious abnormalities. It was therefore possible that one yet unidentified gene might either compensate or antagonize for the absence or for overexpression, respectively, of Dlk1 in those animals. In database searches, we found a novel gene, EGFL9, encoding for a protein whose structural features are virtually identical to those of dlk1, suggesting it may function in a similar way. As dlk1 does, the protein encoded by EGFL9/Dlk2 affects adipogenesis of 3T3-L1 preadipocytes and mesenchymal C3H10T1/2 cells; however, it does so in an opposite way to that of dlk1. In addition, expression levels of both genes appear to be inversely correlated in both cell lines. Moreover, enforced changes in the expression of one gene affect the expression levels of the other. Our data suggest that adipogenesis may be modulated by the coordinated expression of Dlk1 and EGFL9/Dlk2.

Restricted co-expression of Dlk1 and the reciprocally imprinted non-coding RNA, Gtl2: implications for cis-acting control

Dlk1 and Gtl2 are reciprocally imprinted neighboring genes located within a 1 Mb imprinted domain on murine distal chromosome 12. The two genes are expressed and developmentally regulated during mammalian embryogenesis. Dlk1/Pref1 encodes a transmembrane protein with homology to members of the Notch/Delta developmental signaling pathway and Gtl2 generates alternatively spliced poly-adenylated transcripts lacking a conserved open reading frame. An intergenic differentially methylated region (IG-DMR) located 13 kb upstream of Gtl2 has been shown to regulate imprinting throughout the domain by an as yet unknown mechanism. In order to gain insights into regulation at this domain and to compare it with imprinting control at other loci, we compared the expression profile of Dlk1 with Gtl2 during mouse embryogenesis in normal conceptuses and in those with uniparental disomy for chromosome 12. The expression profile of these genes suggests a causative role for Dlk1 and Gtl2 in the pathologies found in uniparental disomy animals, characterized by defects in skeletal muscle maturation, bone formation, placenta size and organization and prenatal lethality. Here, we show restricted overlap in cellular expression of these two genes throughout development. Dlk1 is imprinted and expressed in cell types within the lung, liver and placenta where Gtl2 is not expressed. Gtl2 is highly expressed in the central nervous system (CNS), whereas Dlk1 is found localized to specific regions such as the hypothalamus. Co-expression is observed in most of the mesodermal-derived tissues, notably the skeletal muscle where both genes are strongly co-expressed. In this tissue, Dlk1 shows a relaxation of imprinting with some expression from the maternal allele. These findings indicate that the general mechanism of imprinting at the stages analyzed is not through the co-ordinate non-coding RNA or insulator mechanisms observed for other imprinted domains, and suggest that the two genes have independent tissue-specific functions.

DLK1: increased expression in gliomas and associated with oncogenic activities

DLK1 (delta-like) is a transmembrane and secreted protein in the epidermal growth factor-like homeotic family. Although expressed widely during embryonic development, only a few tissues retain the expression in adults. Neuroendocrine tumors often highly express this protein; therefore, we hypothesized that brain tumors might also express it. This study found that the expression of DLK1 in gliomas was higher than that in normal brain (P < 0.05). After stable transfection of a DLK1 cDNA expression vector into GBM cell lines, their proliferation was increased. Furthermore, they lost contact inhibition, had enhanced anchorage-independent growth in soft agar, and had significantly greater capacity to migrate. Western blot studies showed that expression of cyclin D1, CDK2, and E2F4 were increased, and Rb levels were decreased in these cells. DLK1 was found on the cell surface and secreted in the medium from the transfected GBM cells. DLK1-enriched condition medium stimulated the growth of glioblastoma multiforme cell lines and explants. DLK1 antibody blocked cell growth stimulated by DLK1. In summary, these results suggest that DLK1 may play a role in the formation or progression of gliomas.

Identification of DLK1 variants in pituitary- and neuroendocrine tumors

In a gene chip analysis of common pituitary tumor types, one of the genes with the most impressive tissue-specific expression regulation was delta-like 1 (DLK1), which was strongly expressed in GH-secreting (GH-S) pituitary tumors. In addition to pituitary adenomas, various endocrine tumors were subjected to real-time-quantitative PCR revealing high expression of DLK1 in normal pituitary tissue, in GH-S-, in one prolactin-secreting pituitary adenoma and in pheochromocytomas. Additionally, three DLK1 gene-derived subvariants were identified. The first, lacking 204 bp--coding for epidermal growth factor-like domain 6 and parts of the juxtamembrane region--was named Secredeltin. In the other two splice variants (named Brevideltin and Brevideltinin), a stop codon is introduced due to a frame-shift, leading to truncated proteins of 204 and 213 aas, respectively.

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.

Differential expression of delta-like gene and protein in neuroblastoma, ganglioneuroblastoma and ganglioneuroma

Neuroblastoma is an extremely malignant solid tumor in children, characterized by spontaneous differentiation and regression. An epidermal growth factor-like homeotic protein, delta-like (dlk), has been involved in differentiation of neuroblastoma cell lines, but is unknown in in vivo expression of neuroblastoma. By using in situ hybridization and immunohistochemistry, dlk mRNA and protein expression were studied in formalin-fixed archival tissues from 10 patients with neuroblastoma, five with ganglioneuroblastoma, and five with ganglioneuroma. Three adrenal tissues from children died of diseases other than adrenal tumors and one from an adult with pheochromocytoma were severed as normal and disease controls. The results showed strong immunoreactive dlk staining in endothelial cells in neuroblastoma, ganglioneuroblastoma and ganglioneuroma. Dlk was detectable in mature neuromatous stroma and gangliocytes of ganglioneuroma, but not in neuroblasts of neuroblastoma and ganglioneuroblastoma, neither in gangliocytes of ganglioneuroblastoma. In contrast, dlk mRNA expression was mainly observed in the gangliocytes, but was less intense in the neuroblasts and neuromatous stroma cells. Endothelial cells were essentially devoid of dlk mRNA expression. The findings indicated that there is differential expression of dlk gene and protein among neuroblastoma, ganglioneuroblastoma and ganglioneuroma. The stronger expression of dlk in gangliocytes in ganglioneuroma, in contrast to weaker or no expression in gangliocytes in ganglioneuroblastoma and neuroblasts in neuroblastoma, suggests upregulation of dlk during differentiation of neuroblastoma into more benign form. Furthermore, higher dlk protein expression in the tumor endothelium than in the endothelium of normal adrenal gland implies that dlk may regulate the endothelial function in neuroblastic tumors.

Imprinting, expression, and localisation of DLK1 in Wilms tumours

BACKGROUND

Loss of imprinting (LOI) of the H19/IGF2 domain is a common feature of Wilms tumour. The GTL2/DLK1 domain is also imprinted and is structurally similar to H19/IGF2. The question arises as to whether DLK1 also undergoes LOI in Wilms tumour, or whether the LOI mechanism is restricted to the H19/IGF2 domain.

AIM

To investigate the imprinting status of DLK1 in Wilms tumours with IGF2 LOI. The cellular localisation of DLK1 in the tumours was also examined.

METHODS

DLK1 expression was measured by quantitative real time polymerase chain reaction (Q-PCR) in 30 Wilms tumours that had previously been classified according to whether they had IGF2 LOI, WT1 mutations, or 11p15.5 loss of heterozygosity. Allele specific expression of DLK1 was examined by direct sequencing using a DLK1 exon 5 polymorphism (rs1802710). Immunohistochemical analysis of DLK1 was performed on 13 tumours and two intralobar nephrogenic rests, in addition to two fetal kidneys and one fetal skeletal muscle sample.

RESULTS

Ten of 30 tumours were heterozygous for rs1802710 and all tumours showed retention of imprinting of DLK1. Moderate to high expression of DLK1 was detected by Q-PCR in nine of 13 tumours with myogenic differentiation. Immunohistochemical expression of DLK1 was detected in the myogenic elements.

CONCLUSION

LOI does not occur at the GTL2/DLK1 domain in Wilms tumour. This finding suggests that LOI at 11p15.5 does not reflect non-specific disruption of a shared imprinting mechanism. DLK1 expression in Wilms tumour might reflect the presence of myogenic differentiation, rather than an alteration of its imprinting status.

Transit-amplifying ductular (oval) cells and their hepatocytic progeny are characterized by a novel and distinctive expression of delta-like protein/preadipocyte factor 1/fetal antigen 1

Hepatic regeneration from toxic or surgical injury to the adult mammalian liver, endorses different cellular responses within the hepatic lineage. The molecular mechanisms determining commitment of a cell population at a specific lineage level to participate in liver repair as well as the fate of its progeny in the hostile environment created by the injury are not well defined. Based on the role of the Notch/Delta/Jagged system in cell fate specification and recent reports linking Notch signaling with normal bile duct formation in mouse and human liver, we examined the expression of Notch1, Notch2, Notch3, Delta1, Delta3, Jagged1, and Jagged2, and delta-like protein/preadipocyte factor 1/fetal antigen 1 (dlk) in four well-defined experimental rat models of liver injury and regeneration. Although Delta3 and Jagged2 were undetectable by reverse transcriptase-polymerase chain reaction and Northern blot, we observed the most significant up-regulation of all other transcripts in the 2-acetylaminofluorene-70% hepatectomy (AAF/PHx) model, in which liver mass is restored by proliferation and differentiation of transit-amplifying ductular (oval) cells. The most profound change was observed for dlk. Accordingly, immunohistochemical analyses in the AAF/PHx model showed a specific expression of dlk in atypical ductular structures composed of oval cells. Delta-like protein was not observed in proliferating hepatocytes or bile duct cells after partial hepatectomy or ligation of the common bile duct whereas clusters of dlk immunoreactive oval cells were found in both the retrorsine and the AAF/PHx models. Finally, we used dlk to isolate alpha-fetoprotein-positive cells from fetal and adult regenerating rat liver by a novel antibody panning technique.

Gene expression profiles of mouse submandibular gland development: FGFR1 regulates branching morphogenesis in vitro through BMP- and FGF-dependent mechanisms

Analyses of gene expression profiles at five different stages of mouse submandibular salivary gland development provide insight into gland organogenesis and identify genes that may be critical at different stages. Genes with similar expression profiles were clustered, and RT-PCR was used to confirm the developmental changes. We focused on fibroblast growth factor receptor 1 (FGFR1), as its expression is highest early in gland development. We extended our array results and analyzed the developmental expression patterns of other FGFR and FGF isoforms. The functional significance of FGFR1 was confirmed by submandibular gland organ culture. Antisense oligonucleotides decreased expression of FGFR1 and reduced branching morphogenesis of the glands. Inhibiting FGFR1 signaling with SU5402, a FGFR1 tyrosine kinase inhibitor, reduced branching morphogenesis. SU5402 treatment decreased cell proliferation but did not increase apoptosis. Fgfr, Fgf and Bmp gene expression was localized to either the mesenchyme or the epithelium by PCR, and then measured over time by real time PCR after SU5402 treatment. FGFR1 signaling regulates Fgfr1, Fgf1, Fgf3 and Bmp7 expression and indirectly regulates Fgf7, Fgf10 and Bmp4. Exogenous FGFs and BMPs added to glands in culture reveal distinct effects on gland morphology. Glands cultured with SU5402 were then rescued with exogenous BMP7, FGF7 or FGF10. Taken together, our results suggest specific FGFs and BMPs play reciprocal roles in regulating branching morphogenesis and FGFR1 signaling plays a central role by regulating both FGF and BMP expression.

Physiological functions of imprinted genes

Genomic imprinting in gametogenesis marks a subset of mammalian genes for parent-of-origin-dependent monoallelic expression in the offspring. Embryological and classical genetic experiments in mice that uncovered the existence of genomic imprinting nearly two decades ago produced abnormalities of growth or behavior, without severe developmental malformations. Since then, the identification and manipulation of individual imprinted genes has continued to suggest that the diverse products of these genes are largely devoted to controlling pre- and post-natal growth, as well as brain function and behavior. Here, we review this evidence, and link our discussion to a website (http://www.otago.ac.nz/IGC) containing a comprehensive database of imprinted genes. Ultimately, these data will answer the long-debated question of whether there is a coherent biological rationale for imprinting.

Expression of preadipocyte factor-1(Pref-1), a delta-like protein, in healing mouse ears

Preadipocyte factor-1 (Pref-1), a delta-like protein containing epidermal growth factor-repeats, is expressed in proliferating cells in a variety of tissues and is believed to be involved in maintaining the undifferentiated state of these cells. Using microarray analysis, reverse transcriptase-polymerase chain reaction, in-situ hybridization, and immunohistochemistry, we have identified Pref-1 expression in the healing ears of two strains of mice, MRL and C57BL/6. MRL is unusual in that ear punches completely regenerate the ear tissue along with new cartilage with no scarring. Pref-1 is more highly expressed in the MRL wounds, is uniquely found in a condensation of cells within the regenerating tissue of the blastema, and may contribute to the regenerative capacity of the MRL ear wound.

The EGF-like homeotic protein dlk affects cell growth and interacts with growth-modulating molecules in the yeast two-hybrid system

Levels of dlk, an EGF-like homeotic protein, are critical for several differentiation processes. Because growth and differentiation are, in general, exclusive of each other, and increasing evidence indicates that Dlk1 expression changes in tumorigenic processes, we studied whether dlk could also affect cell growth. We found that, in response to glucocorticoids, Balb/c 3T3 cells with diminished levels of dlk expression develop foci-like cells that have lost contact inhibition, display altered morphology, and grow faster than control cell lines. Balb/c 3T3 cells spontaneously growing more rapidly are also dlk-negative cells. Moreover, screening by the yeast two-hybrid system, using Dlk1 constructs as baits, resulted in the isolation of GAS1 and acrogranin cDNAs. Interestingly, these proteins are cysteine-rich molecules involved in the control of cell growth. Taken together, these observations suggest that dlk may participate in a network of interactions controlling how the cells respond to growth or differentiation signals.

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.

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.

Genomic organization and genetic mapping of the bovine PREF-1 gene

As a potential regulator of nutrient partitioning in beef cattle, we have cloned and genetically mapped the bovine PREF-1 gene. A full-length PREF-1 cDNA was isolated by iterative purification from a mixed-tissue cDNA library to which adipose contributed mRNA. Analysis of partial cDNAs from this library revealed that the 3'-terminal exon of the bovine PREF-1 mRNA is spliced in a manner analogous to its murine ortholog. However, we have also detected a PREF-1 splice form apparently unique to cattle. Aside from this alternative selection of a splice donor in the bovine fifth exon, the exon/intron junctions of the bovine PREF-1 gene recapitulate those observed for mice. The sequences proximal to the bovine PREF-1 transcription start site are homologous to the mouse PREF-1 promoter. Importantly, the sequence experimentally identified as critical to PREF-1 "suppression in adipocyte differentiation" is conserved in the bovine gene. The bovine PREF-1 gene was mapped to the telomeric end of BTA 21 by virtue of a physically linked microsatellite with seven alleles and 285 informative meiosis.

On the development of the islets of Langerhans

Studies of pancreatic development have suggested that the islet cells develop through multihormonal stages. Abundant data have confirmed that multihormonal cells are common during pancreatic development. A number of transcription factors and homeotic proteins have also been found to be important to pancreatic and islet cell development. While one of these factors (Isl1) is important for the development of the dorsal pancreatic bud and mesenchyme, another factor (Pdx1) is needed for growth and branching of both pancreatic buds. Studies of the expression patterns of pancreatic hormones and transcription factors and other marker proteins seem at present to be most compatible with the view that early glucagon and glucagon + insulin expressing cells are precursors to the glucagon cells of the islets while mature B cells arise through differentiation from glucagon-negative precursor cells. Recent data also point to possibilities of local paracrine interactions between islet cell types and the parenchymal tissue during development.

Rat endocrine pancreatic development in relation to two homeobox gene products (Pdx-1 and Nkx 6.1)

We studied the distribution of the homeodomain proteins Pdx-1 and Nkx 6.1 in the developing rat pancreas. During early development, nuclear staining for both Pdx-1 and Nkx 6.1 occurred in most epithelial cells of the pancreatic anlage. Subsequently, Nkx 6.1 became more beta-cell-restricted, and Pdx-1 also occurred in other islet cell types and in the duodenal epithelium. During early pancreatic development, cells co-storing insulin and glucagon were regularly detected. The vast majority of these did not possess nuclear staining for either Pdx-1 or Nkx 6.1. Subsequently, cells storing insulin only appeared. Such cells displayed strongly Pdx-1- and Nkx 6.1-positive nuclei. Therefore, Nkx 6.1, like Pdx-1, may be an important factor in pancreatic development and in mature insulin cell function.

Fetal antigen 1 (FA1), a circulating member of the epidermal growth factor (EGF) superfamily: ELISA development, physiology and metabolism in relation to renal function

We describe an ELISA technique for quantification of fetal antigen 1 (FA1), a glycoprotein belonging to the EGF-superfamily. The ELISA is based on immunospecifically purified polyclonal antibodies and has a dynamic range of 0.7-5.3 ng/ml, intra- and inter-assay C.V.s of less than 3.2% and an average recovery of 105% in serum and 98% in urine. Comparison of FA1 in amniotic fluid, serum and urine revealed parallel titration curves, identical elution volumes following size chromatography, immunological identity and similar profiles when analysed by MALDI-MS. The reference interval for serum FA1 was 12.3-46.6 ng/ml and the levels were 10 times higher in patients with renal failure. FA1 showed no diurnal variation, no variation during the menstrual cycle and was not influenced by the acute phase reaction. In humans (n = 10) the renal clearance of FA1 was 11 ml/min and an identical high renal clearance was found in rats when expressed per 100 g body weight. In rats the initial increase in serum FA1 was 10 ng/ml/h following bilateral nephrectomy, explaining the increased serum concentrations of FA1 observed in patients with renal failure.

Growth hormone and prolactin stimulate the expression of rat preadipocyte factor-1/delta-like protein in pancreatic islets: molecular cloning and expression pattern during development and growth of the endocrine pancreas

GH and PRL have been shown to stimulate proliferation and insulin production in islets of Langerhans. To identify genes regulated by GH/PRL in islets, we performed differential screening of a complementary DNA library from neonatal rat islets cultured for 24 h with human GH (hGH). One hGH-induced clone had 96% identity with mouse preadipocyte factor-1 (Pref-1, or delta-like protein (Dlk)]. The size of Pref-1 messenger RNA (mRNA) in islets was 1.6 kilobases, with two less abundant mRNAs of 3.7 and 6.2 kilobases. The Pref-1 mRNA content of islets from adult rats was only 1% of that in neonatal islets. Pref-1 mRNA was markedly up-regulated in islets from pregnant rats from day 12 to term compared with those from age-matched female rats. Two peaks in mRNA expression were observed during gestation, one on day 14 and the other at term, whereafter it decreased to nonpregnant levels. Pref-1 mRNA was up-regulated 3- to 4-fold in neonatal rat islets of Langerhans after 48-h culture with hGH, as found also with bovine GH or ovine PRL. During the development of pancreas from embryonic day 12 (E12) to postnatal day 4, we observed a 2-fold increase in Pref-1 mRNA on E17 and a 5-fold increase at birth, followed by a rapid decline on postnatal day 4. Pref-1 immunoreactivity was found in a subpopulation of insulin cells of neonatal islets of Langerhans. At an early embryonal stage (E13), most cells of the pancreatic anlage were Pref-1 positive, becoming predominantly restricted to the insulin-producing cells during development. In conclusion, these findings suggest that Pref-1 is involved in both differentiation and growth of beta-cells.