A Novel Mesoderm-Specific cDNA Isolated from a Mouse Embryonal Carcinoma Cell Line. (embryonal carcinoma cell/cDNA/in situ hybridization/mesoderm/mouse embryo)

Regeneration-specific promoter switching facilitates Mest expression in the mouse digit tip to modulate neutrophil response

The mouse digit tip regenerates following amputation, a process mediated by a cellularly heterogeneous blastema. We previously found the gene Mest to be highly expressed in mesenchymal cells of the blastema and a strong candidate pro-regenerative gene. We now show Mest digit expression is regeneration-specific and not upregulated in post-amputation fibrosing proximal digits. Mest homozygous knockout mice exhibit delayed bone regeneration though no phenotype is found in paternal knockout mice, inconsistent with the defined maternal genomic imprinting of Mest. We demonstrate that promoter switching, not loss of imprinting, regulates biallelic Mest expression in the blastema and does not occur during embryogenesis, indicating a regeneration-specific mechanism. Requirement for Mest expression is tied to modulating neutrophil response, as revealed by scRNAseq and FACS comparing wildtype and knockout blastemas. Collectively, the imprinted gene Mest is required for proper digit tip regeneration and its blastema expression is facilitated by promoter switching for biallelic expression.

Mouse mesoderm-specific transcript inhibits adipogenic differentiation and induces trans-differentiation into hepatocyte-like cells in 3T3-L1 preadiocytes

OBJECTIVE

The mesoderm-specific transcript (Mest) is an imprinted gene that is transcribed from the paternal allele. It is a marker of adipose tissue expansion; however, it is uncertain whether Mest expression promotes or suppresses adipogenic differentiation. To elucidate the effects of Mest expression on adipogenic differentiation, we transfected an expression vector or siRNA for mouse Mest into 3T3-L1 mouse preadipocyte cell line.

RESULTS

In differentiated 3T3-L1 adipocytes, Mest overexpression decreased lipid accumulation. Conversely, gene silencing of Mest increased the accumulation of lipid droplets in adipocytes. These results demonstrate that Mest negatively regulates adipocyte differentiation. Further, Mest induced trans-differentiation of 3T3-L1 cells into hepatocytes, and its overexpression induced the expression of hepatocyte marker genes, including albumin and α-fetoprotein. In the presence of dexamethasone, the forced expression of the Mest caused morphological changes in 3T3-L1 cells. Cells were flat and polygonal shapes, with an increased accumulation of intracellular glycogen and other features that are typical of hepatocytes. Therefore, Mest inhibits adipogenic differentiation of 3T3-L1 preadipocytes by inducing hepatocyte trans-differentiation.

Effects of Cryopreservation on Sperm with Cryodiluent in Viviparous Black Rockfish (Sebastes schlegelii)

Black rockfish is an economically important fish in East Asia. Little mention has been paid to the sperm cryopreservation in black rockfish. In this study, the optimal cryodiluent was selected from 48 combinations by detecting various sperm parameters. Transcriptome and methylome analysis were further performed to explore the molecular mechanism of inevitable cryoinjuries. The results showed that cryopreservation had negative effects on the viability, DNA integrity, mitochondrial activity, total ATPase and LDH of sperm even with optimal cryodiluent (FBS + 15% Gly). Transcriptome and methylome analysis revealed that the expression of 179 genes and methylation of 1266 genes were affected by cryopreservation. These genes were enriched in GO terms of death, G-protein coupled receptor signaling pathway, response to external stimulus and KEGG pathways of phospholipase D signaling pathway and xenobiotic and carbohydrate metabolism pathways. The role of PIK3CA and CCNA2 were highlighted in the protein-protein interaction network, and the sperm quality-related imprinted gene mest was identified among the 7 overlapping genes between transcriptome and methylome. Overall, the cryodiluent for black rockfish sperm was optimized, providing a feasible method for cryopreservation. The transcriptome and methylome data further demonstrated the underlying molecular mechanisms of cryoinjuries, proving clues for improvement of cryopreservation method of black rockfish.

Hypermethylation of Mest promoter causes aberrant Wnt signaling in patients with Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that leads to dementia and behavioral changes. Extracellular deposition of amyloid plaques (Aβ) and intracellular deposition of neurofibrillary tangles in neurons are the major pathogenicities of AD. However, drugs targeting these therapeutic targets are not effective. Therefore, novel targets for the treatment of AD urgently need to be identified. Expression of the mesoderm-specific transcript (Mest) is regulated by genomic imprinting, where only the paternal allele is active for transcription. We identified hypermethylation on the Mest promoter, which led to a reduction in Mest mRNA levels and activation of Wnt signaling in brain tissues of AD patients. Mest knockout (KO) using the CRIPSR/Cas9 system in mouse embryonic stem cells and P19 embryonic carcinoma cells leads to neuronal differentiation arrest. Depletion of Mest in primary hippocampal neurons via lentivirus expressing shMest or inducible KO system causes neurodegeneration. Notably, depletion of Mest in primary cortical neurons of rats leads to tau phosphorylation at the S199 and T231 sites. Overall, our data suggest that hypermethylation of the Mest promoter may cause or facilitate the progression of AD.

AUTS2 isoforms control neuronal differentiation

Mutations in AUTS2 are associated with autism, intellectual disability, and microcephaly. AUTS2 is expressed in the brain and interacts with polycomb proteins, yet it is still unclear how mutations in AUTS2 lead to neurodevelopmental phenotypes. Here we report that when neuronal differentiation is initiated, there is a shift in expression from a long isoform to a short AUTS2 isoform. Yeast two-hybrid screen identified the splicing factor SF3B1 as an interactor of both isoforms, whereas the polycomb group proteins, PCGF3 and PCGF5, were found to interact exclusively with the long AUTS2 isoform. Reporter assays showed that the first exons of the long AUTS2 isoform function as a transcription repressor, but the part that consist of the short isoform acts as a transcriptional activator, both influenced by the cellular context. The expression levels of PCGF3 influenced the ability of the long AUTS2 isoform to activate or repress transcription. Mouse embryonic stem cells (mESCs) with heterozygote mutations in Auts2 had an increase in cell death during in vitro corticogenesis, which was significantly rescued by overexpressing the human AUTS2 transcripts. mESCs with a truncated AUTS2 protein (missing exons 12-20) showed premature neuronal differentiation, whereas cells overexpressing AUTS2, especially the long transcript, showed increase in expression of pluripotency markers and delayed differentiation. Taken together, our data suggest that the precise expression of AUTS2 isoforms is essential for regulating transcription and the timing of neuronal differentiation.

Tumor Necrosis Factor α Influences Phenotypic Plasticity and Promotes Epigenetic Changes in Human Basal Forebrain Cholinergic Neuroblasts

TNFα is the main proinflammatory cytokine implicated in the pathogenesis of neurodegenerative disorders, but it also modulates physiological functions in both the developing and adult brain. In this study, we investigated a potential direct role of TNFα in determining phenotypic changes of a recently established cellular model of human basal forebrain cholinergic neuroblasts isolated from the nucleus basalis of Meynert (hfNBMs). Exposing hfNBMs to TNFα reduced the expression of immature markers, such as nestin and β-tubulin III, and inhibited primary cilium formation. On the contrary, TNFα increased the expression of TNFα receptor TNFR2 and the mature neuron marker MAP2, also promoting neurite elongation. Moreover, TNFα affected nerve growth factor receptor expression. We also found that TNFα induced the expression of DNA-methylation enzymes and, accordingly, downregulated genes involved in neuronal development through epigenetic mechanisms, as demonstrated by methylome analysis. In summary, TNFα showed a dual role on hfNBMs phenotypic plasticity, exerting a negative influence on neurogenesis despite a positive effect on differentiation, through mechanisms that remain to be elucidated. Our results help to clarify the complexity of TNFα effects in human neurons and suggest that manipulation of TNFα signaling could provide a potential therapeutic approach against neurodegenerative disorders.

Peg1/Mest, an imprinted gene, is involved in mammary gland maturation

Imprinted genes, which are specific to mammals, play important roles in cell proliferation, differentiation, ontogeny, and other phenomena. Moreover, these genes are considered crucial in the research of mammalian evolution. In the current study, we investigated the association between the expression of paternally imprinted gene paternally expressed 1/mesoderm-specific transcript (Peg1/Mest) and the maturation of the mammary gland. Quantitative real-time polymerase chain reaction analysis of Peg1/Mest gene expression at different stages of mouse mammary gland maturation revealed that its expression increased during gestation but decreased during lactation. Immunohistochemical staining demonstrated that Peg1/Mest was expressed in mammary epithelial cells. We measured expression levels of Peg1/Mest and E-cadherin during mammary alveoli formation using immunofluorescence staining a cell model for mammary alveoli formation in a 3D culture system. We found that the onset of E-cadherin expression roughly coincided with the peak of Peg1/Mest expression. Moreover, we discovered that the formation and proliferation of alveoli were suppressed in Peg1/Mest knockdown mammary epithelial cells. These results suggest that Peg1/Mest plays a certain role in mammary alveoli formation. To clarify the role of Peg1/Mest in the lactogenic differentiation of mammary epithelial cells, we examined the lactogenic differentiation capability of Peg1/Mest-overexpressing HC11 cells. Application of a differentiation-inducing stimulus did not increase β-casein expression in Peg1/Mest-overexpressing HC11 cells. The current study for the first time reports the involvement of an imprinted gene in mammary gland maturation.

Mesoderm-specific transcript (MEST) is a negative regulator of human adipocyte differentiation

BACKGROUND

A growing body of evidence suggests that many downstream pathologies of obesity are amplified or even initiated by molecular changes within the white adipose tissue (WAT). Such changes are the result of an excessive expansion of individual white adipocytes and could potentially be ameliorated via an increase in de novo adipocyte recruitment (adipogenesis). Mesoderm-specific transcript (MEST) is a protein with a putative yet unidentified enzymatic function and has previously been shown to correlate with adiposity and adipocyte size in mouse.

OBJECTIVES

This study analysed WAT samples and employed a cell model of adipogenesis to characterise MEST expression and function in human.

METHODS AND RESULTS

MEST mRNA and protein levels increased during adipocyte differentiation of human multipotent adipose-derived stem cells. Further, obese individuals displayed significantly higher MEST levels in WAT compared with normal-weight subjects, and MEST was significantly correlated with adipocyte volume. In striking contrast to previous mouse studies, knockdown of MEST enhanced human adipocyte differentiation, most likely via a significant promotion of peroxisome proliferator-activated receptor signalling, glycolysis and fatty acid biosynthesis pathways at early stages. Correspondingly, overexpression of MEST impaired adipogenesis. We further found that silencing of MEST fully substitutes for the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) as an inducer of adipogenesis. Accordingly, phosphorylation of the pro-adipogenic transcription factors cyclic AMP responsive element binding protein (CREB) and activating transcription factor 1 (ATF1) were highly increased on MEST knockdown.

CONCLUSIONS

Although we found a similar association between MEST and adiposity as previously described for mouse, our functional analyses suggest that MEST acts as an inhibitor of human adipogenesis, contrary to previous murine studies. We have further established a novel link between MEST and CREB/ATF1 that could be of general relevance in regulation of metabolism, in particular obesity-associated diseases.

Gene expression of mesoderm-specific transcript is upregulated as preadipocytes differentiate to adipocytes in vitro

Mesoderm-specific transcript (Mest) is a distinct gene associated with adipocyte differentiation and proliferation. The mechanisms regulating expression of the Mest gene are not established. Therefore, we investigated Mest gene expression during adipogenic differentiation in murine 3T3-L1 preadipocytes and adipose-derived stromal cells (ADCs) from C57BL/6J mouse adipose tissue. Expression of Mest mRNA increased significantly in 3T3-L1 cells during differentiation. Additionally, Mest mRNA expression levels were additively enhanced by the inhibition of DNA methylation. Expression levels of the Mest gene were also markedly elevated in differentiating ADCs in vitro. Additionally, we showed that Mest mRNA can be upregulated by increasing intracellular cAMP, and that Mest expression is suppressed by inhibition of protein kinase A (PKA). Mest expression was regulated through cAMP-dependent PKA pathways during differentiation of preadipocytes into adipocytes in vitro, supporting the critical role of Mest in proliferation and differentiation of adipocytes.

Tissue-specific alternative polyadenylation at the imprinted gene Mest regulates allelic usage at Copg2

The gene Mest (also known as Peg1) is regulated by genomic imprinting in the mouse and only the paternal allele is active for transcription. MEST is similarly imprinted in humans, where it is a candidate for the growth retardation Silver-Russell syndrome. The MEST protein belongs to an ancient family of hydrolases but its function is still unknown. It is highly conserved in vertebrates although imprinted expression is only observed in marsupials and eutherians, thus a recent evolutionary event. Here we describe the identification of new imprinted RNA products at the Mest locus, longer variants of the RNA, called MestXL, transcribed >10 kb into the downstream antisense gene Copg2. During development MestXL is produced exclusively in the developing central nervous system (CNS) by alternative polyadenylation. Copg2 is biallelically expressed in the embryo except in MestXL-expressing tissues, where we observed preferential expression from the maternal allele. To analyze the function of the MestXL transcripts in Copg2 regulation, we studied the effects of a targeted allele at Mest introducing a truncation in the mRNA. We show that both the formation of the MestXL isoforms and the allelic bias at Copg2 are lost in the CNS of mutants embryos. Our results propose a new mechanism to regulate allelic usage in the mammalian genome, via tissue-specific alternative polyadenylation and transcriptional interference in sense-antisense pairs at imprinted loci.

Gene expression profiling at early organogenesis reveals both common and diverse mechanisms in foregut patterning

The thyroid and lungs originate as neighboring bud shaped outgrowths from the midline of the embryonic foregut. When and how organ specific programs regulate development into structures of distinct shapes, positions and functions is incompletely understood. To characterize, at least in part, the genetic basis of these events, we have employed laser capture microdissection and microarray analysis to define gene expression in the mouse thyroid and lung primordia at E10.5. By comparing the transcriptome of each bud to that of the whole embryo as well as to each other, we broadly describe the genes that are preferentially expressed in each developing organ as well as those with an enriched expression common to both. The results thus obtained provide a valuable resource for further analysis of genes previously unrecognized to participate in thyroid and lung morphogenesis and to discover organ specific as well as common developmental mechanisms. As an initial step in this direction we describe a regulatory pathway involving the anti-apoptotic gene Bcl2 that controls cell survival in early thyroid development.

Alteration of Differentiation Potentials by Modulating GATA Transcription Factors in Murine Embryonic Stem Cells

Background. Mouse embryonic stem (ES) cells can be differentiated in vitro by aggregation and/or retinoic acid (RA) treatment. The principal differentiation lineage in vitro is extraembryonic primitive endoderm. Dab2, Laminin, GATA4, GATA5, and GATA6 are expressed in embryonic primitive endoderm and play critical roles in its lineage commitment. Results. We found that in the absence of GATA4 or GATA5, RA-induced primitive endoderm differentiation of ES cells was reduced. GATA4 (-/-) ES cells express higher level of GATA5, GATA6, and hepatocyte nuclear factor 4 alpha marker of visceral endoderm lineage. GATA5 (-/-) ES cells express higher level of alpha fetoprotein marker of early liver development. GATA6 (-/-) ES cells express higher level of GATA5 as well as mesoderm and cardiomyocyte markers which are collagen III alpha-1 and tropomyosin1 alpha. Thus, deletion of GATA6 precluded endoderm differentiation but promoted mesoderm lineages. Conclusions. GATA4, GATA5, and GATA6 each convey a unique gene expression pattern and influences ES cell differentiation. We showed that ES cells can be directed to avoid differentiating into primitive endoderm and to adopt unique lineages in vitro by modulating GATA factors. The finding offers a potential approach to produce desirable cell types from ES cells, useful for regenerative cell therapy.

Peg1/Mestin obese adipose tissue is expressed from the paternal allele in an isoform-specific manner

Paternally expressed 1 (Peg1)/mesoderm specific transcript (Mest) is an imprinted gene, which is only transcribed from the paternal (father's) allele. In some human cancer tissues, an alternatively spliced variant of PEG1/MEST mRNA using a different promoter of a distinct first exon is expressed from both paternal and maternal alleles. We previously reported that Peg1/Mest expression was markedly up-regulated in obese adipose tissue in mice. Moreover, transgenic overexpression of Peg1/Mest in the adipose tissue resulted in the enlargement of adipocytes in size. Given the potential pathophysiologic relevance in obesity, we examined the nature of increased expression of Peg1/Mest in obese adipose tissue. In obese adipose tissue, expression of Peg1/Mest was increased, but not that of other imprinted genes tested. The transcription rate of Peg1/Mest was increased in obese adipose tissue. We found at least four isoforms of mouse Peg1/Mest generated by use of the alternative first exons. We also demonstrated that the abundantly expressed Peg1/Mest in obese adipose tissue retained monoallelic expression. This is the first report of monoallelic induction of Peg1/Mest in adult tissues.

Structure and expression of the zebrafish mest gene, an ortholog of mammalian imprinted gene PEG1/MEST

PEG1/MEST is a paternally expressed gene in placental mammals. Here, we report identification of zebrafish (Danio rerio) gene mest, an ortholog of mammalian PEG1/MEST. Zebrafish mest encodes a polypeptide of 344 amino acids and shows a significant similarity to mammalian orthologs. Zebrafish mest is present as a single copy in the zebrafish genome and is closely linked to copg2 as in mammals. It is notable that 10 of 11 intron positions in mest are conserved among mammalian PEG1/MEST genes, indicating that the genomic organization and linkage between mest and copg2 loci was established in ancient vertebrates. Zebrafish mest is expressed in blastula, segmentation, and larval stages, exhibiting gradually increased expression as the development proceeds. Allelic expression analysis in hybrid larvae shows that both parental alleles are transcribed. We also observed one-codon alternative splicing involving an alternative usage of the two consecutive splice acceptors of intron 1, generating two protein isoforms with different lengths of a single amino acid.

Mest/Peg1 imprinted gene enlarges adipocytes and is a marker of adipocyte size

Obesity is a common and serious metabolic disorder in the developed world that is occasionally accompanied by type II diabetes, atherosclerosis, hypertension, and hyperlipidemia. We have found that mesoderm-specific transcript (Mest)/paternally expressed gene 1 (Peg1) gene expression was markedly enhanced in white adipose tissue of mice with diet-induced and genetically caused obesity/diabetes but not with streptozotocin-induced diabetes, which does not cause obesity. Administration of pioglitazone, a drug for type II diabetes and activator of peroxisome proliferator-activated receptor (PPAR)gamma, in obese db/db mice reduced the enhanced expression of Mest mRNA in adipose tissue, concomitant with an increase in body weight and a decrease in the size of adipose cells. Ectopic expression of Mest in 3T3-L1 cells caused increased gene expression of adipose markers such as PPARgamma, CCAAT/enhancer binding protein (C/EBP)alpha, and adipocyte fatty acid binding protein (aP)2. In transgenic mice overexpressing Mest in adipose tissue, enhanced expression of the adipose genes was observed. Moreover, adipocytes were markedly enlarged in the transgenic mice. Thus Mest appears to enlarge adipocytes and could be a novel marker of the size of adipocytes.

Loss-of-imprinting ofPeg1 in mouse interspecies hybrids is correlated with altered growth

Previous studies have shown that loss-of-imprinting (LOI) is a regular occurrence in interspecies hybrids of the genus Peromyscus. Furthermore, evidence was presented that indicated that LOI is involved in a placental hybrid dysgenesis effect resulting in abnormal placental growth and thus possibly in speciation. We show here that LOI of the strictly paternally expressed gene Peg1 (also called Mest) occurs in F1 hybrids between Mus musculus (MMU) and M. spretus (MSP). Peg1 LOI is correlated with increased body weight and increased weight of two of the organs tested, kidney and spleen. X-gal staining of tissues derived from Peg1(+/-) x MSP F1 mice, carrying a maternal LacZ knock-in allele of Peg1, demonstrates that LOI is stochastic in that it affects different tissues to variable extents and that, even within one tissue, not all cells are similarly affected. Furthermore, this expression from the maternal allele does not necessarily follow the endogenous paternal Peg1 expression pattern. Our results indicate that LOI occurs in interspecies hybrids in the genus Mus and that altered growth is a frequent outcome of LOI.

Microarray analysis identifies differentiation-associated genes regulated by human papillomavirus type 16 E6

In this study, we used oligonucleotide microarray analysis to determine which cellular genes are regulated by the human papillomavirus type 16 (HPV-16) E6 oncoprotein. We found that E6 causes the downregulation of a large number of cellular genes involved in keratinocyte differentiation, including genes such as small proline-rich proteins, transglutaminase, involucrin, elafin, and cytokeratins, which are normally involved in the production of the cornified cell envelope. In contrast, E6 upregulates several genes, such as vimentin, that are usually expressed in mesenchymal lineages. E6 also modulates levels of genes involved in inflammation, including Cox-1 and Nag-1. By using E6 mutants that differentially target p53 for degradation, we determined that E6 regulates cellular genes by both p53-dependent and independent mechanisms. The microarray data also indicate that HPV-16 E6 modulates certain effects of HPV-16 E7 on cellular gene expression. The identification of E6-regulated genes in this analysis provides a basis for further studies on their role in HPV infection and cellular transformation.

Imprinted mesodermal specific transcript (MEST) and H19 genes in renal development and diabetes

BACKGROUND

Imprinted genes, mesodermal specific cDNA or transcript (MEST) and H19, are implicated in peri-implantation embryogenesis, and their expression was assessed in embryonic kidneys undergoing glucose-induced dysmorphogenesis.

METHODS

MEST and H19 mRNA expression was assessed by Northern blot analysis in embryonic kidneys of mice harvested at day 15 to day 19 of gestation and of 1-week-old mice obtained from hyperglycemic mothers. A full-length mouse MEST cDNA was isolated, subcloned into an expression vector, a recombinant protein prepared and an antibody raised; the latter was used to assess protein expression by immunoprecipitation and immunofluorescence microscopy in day 13 metanephric explants subjected to high glucose ambience. Also, MEST mRNA expression was assessed in high d glucose-treated explants by competitive reverse transcription-polymerase chain reaction (RT-PCR) analyses and by in situ tissue autoradiography.

RESULTS

A high expression of MEST and H19 with respective transcript size of approximately 2.7 and approximately 2.4 kb was observed in fetal kidneys, and their expression decreased during the successive stages of gestation and was undetectable in the postnatal period. At day 13, the MEST mRNA was expressed in the mesenchyme, while H19 was expressed in the ureteric bud branches and epithelial elements of the metanephros. Their expression decreased with progression of gestation. By competitive RT-PCR and Northern blot and in situ autoradiographic analyses, both MEST and H19 expressions decreased in day 13 explants treated with high glucose and in the kidneys of fetuses obtained from diabetic mothers. The MEST protein expression was observed in the metanephric epithelial elements and ureteric bud branches instead of in the mesenchyme, and its expression decreased in glucose-treated dysmorphogenetic explants, as assessed by immunofluorescence and immunoprecipitation methods.

CONCLUSION

MEST and H19 imprinted genes are strategically located in the mammalian embryonic metanephros. They are developmentally regulated and their concomitant decreased expression in high glucose ambience or diabetic state did not follow the prevailing dogma of reciprocal inactivation/activation of imprinted genes, and such a decrease may be responsible for the perturbed epithelial:mesenchymal interactions leading to dysmorphogenesis of the mammalian metanephros.

Expression ofPeg1 (Mest) in the developing mouse heart: Involvement in trabeculation

Peg1 (Mest) is an imprinted gene of unknown function widely expressed in the mouse embryo, predominantly in cells of the mesodermal lineage. We have revealed a restricted expression pattern within the developing heart. Initial uniform expression throughout the linear heart tube subsequently becomes restricted, primarily to the developing myocardial trabeculae of both the atria and ventricles, where it persists into late development. Expression in the atrial appendage myocardium precedes the emergence of trabeculae (pectinate muscles), and occurs earlier and to a greater extent on the right than on the left, reflecting the spatial and temporal pattern of trabeculation. Analysis of myocardial morphology in mice lacking the Peg1 gene, which are viable and appear grossly normal, reveals a subtle alteration in the pattern of trabeculation: an increase in thickness and reduction in density of the compact myocardium, similar to that seen in the human cardiomyopathy ventricular noncompaction.

Identification of developmentally regulated mesodermal-specific transcript in mouse embryonic metanephros

Mesodermal-specific cDNA or transcript (MEST) was identified by suppression subtractive hybridization-PCR of cDNA isolated from embryonic day 13 vs. newborn mice kidneys. At day 13 of mouse gestation, a high expression of MEST, with a single approximately 2.7-kb transcript that was exclusively localized to the metanephric mesenchyme was observed. The MEST mRNA expression gradually decreased during the later stages and then abruptly decreased in the newborn kidneys and subsequent postnatal life, after which a very mild expression persisted in the glomerular mesangium. Regression in mRNA expression during embryonic renal development appears to be related to methylation of the MEST gene. Treatment of metanephroi, harvested at day 13 of gestation with MEST-specific antisense oligodeoxynucleotide resulted in a dose-dependent decrease in the size of the explants and the nephron population. This was associated with a selective decrease in MEST mRNA expression and accelerated apoptosis of the mesenchyme. These findings suggest that MEST, a gene with a putative mesenchymal cell-derived protein, conceivably plays a role in mammalian metanephric development.

Unregulated expression of the imprinted genes H19 and Igf2r in mouse uniparental fetuses

The present study shows that the H19 and Igf2r genes, which are imprinted and expressed solely from maternal alleles, are expressed in an unregulatable manner in mouse uniparental, androgenetic, and parthenogenetic fetuses at day 9.5 of gestation. In the androgenetic fetuses, the H19 and Igf2r genes were respectively expressed at 12 and 40% of the levels in biparental fetuses. In addition, the expression of both genes was excessive (1259 and 482%, respectively) in the parthenotes. These expressions of the imprinted genes were not regulated by methylation in the regulatory regions. Moreover, the expression of the antisense Igf2r RNA (Air) was also excessive and was not correlated with Igf2r gene expression in the uniparental fetuses. Taken together, these results indicate that the parental specific expression of imprinted genes is not maintained in particular genes in uniparental embryos, which in turn suggests that both parental genomes are required to establish maternal specific expression of the H19 and Igf2r genes by trans-acting mechanisms.

Expression of the imprinted genes MEST/Mest in human and murine placenta suggests a role in angiogenesis

In the mouse fetus, Mest is widely expressed in mesoderm derived tissues. In separate studies in mice and in humans, it has been shown to be maternally imprinted, that is, only the paternally inherited allele is active. Here, we show that starting with implantation, Mest is also expressed in maternal decidua of the mouse and in placenta of both humans and mice. Expression in murine decidua was restricted to endothelial cells. After Day 7, expression in the decidua gradually decreased. Mest-specific RT-PCR and restriction fragment length variant (RFLV) analysis of decidualized endometrium isolated from (M. musculus x M. spretus)F1 females showed that only the paternally derived Mest allele was activated in the decidual endothelium. In the mouse extraembryonic tissues, Mest transcripts were detected in derivatives of extraembryonic mesoderm only. Here, hemangioblast precursor cells and endothelial cells were positive. At all developmental stages of the mouse, trophoblast-derived cells were clearly devoid of Mest transcripts. In the human placenta MEST transcripts were also detected in hemangioblast precursor cells, however, MEST was also expressed in villous and invasive cytotrophoblast. In a human choriocarcinoma/trophoblastic tumour grown in a nude mouse, human MEST was expressed in the tumour cells, whereas murine Mest was expressed in endothelia of the murine capillaries. The expression pattern exhibited by both Mest and MEST in extraembryonic tissues during development and during formation of choriocarcinoma/trophoblast tumour suggests a functional role of the MEST proteins related to oncofetal angiogenesis. Dev Dyn 2000;217:1-10.

gamma2-COP, a novel imprinted gene on chromosome 7q32, defines a new imprinting cluster in the human genome

We describe a novel imprinted gene, gamma 2-COP (nonclathrincoatprotein), identified in a search for expressed sequences in human chromosome 7q32 where the paternally expressed MEST gene is located. gamma 2-COP contains 24 exons and spans >50 kb of genomic DNA. Like MEST, gamma 2-COP is ubiquitously transcribed in fetal and adult tissues. In fetal tissues, including skeletal muscle, skin, kidney, adrenal, placenta, intestine, lung, chorionic plate and amnion, gamma 2-COP is imprinted and expressed from the paternal allele. In contrast to the monoallelic expression observed in these fetal tissues, biallelic expression was evident in fetal brain and liver and in adult peripheral blood. Biallelic expression in blood is supported by the demonstration of gamma 2-COP transcripts in lymphoblastoid cell lines with maternal uniparental disomy 7. Absence of paternal gamma 2-COP transcripts during embryonic development may contribute to Silver-Russell syndrome. However, on mutation scanning the only gamma 2-COP mutation detected was maternally derived. Amino acid comparison of gamma2-COP protein revealed close relation to gamma-COP, a subunit of the coatomer complex COPI, suggesting a role of gamma2-COP in cellular vesicle traffic. The existence of distinct coatomer complexes could be the basis for the functional heterogeneity of COPI vesicles in retrograde and anterograde transport and/or in cargo selection. Together, gamma 2-COP and MEST constitute a novel imprinting cluster in the human genome that may contain other, as yet unknown, imprinted genes.

Effect of CpG methylation on expression of the mouse imprinted gene Mest

We previously reported isolation of the mouse gene, Mest (mesoderm-specific transcripts), which is mapped to the proximal part of chromosome 6 and predominantly expressed in the mesoderm and its derivatives during development. Peg1, a paternally expressed gene isolated by a systematic screening of imprinted genes, was recently demonstrated to be identical to Mest. We and others have shown that the human homolog (MEST) of Mest is also imprinted so as to be expressed from the paternal copy and maps to 7q32. To study transcriptional regulation of Mest/Peg1, we examined the effect of DNA methylation on its expression. In the embryonal carcinoma (EC) cell line, MC12, from which Mest was originally isolated, the 5'-region harboring presumptive promoter of the gene was undermethylated. On the other hand, C4XX, a subclone of MC12 which had lost expression of Mest, was characterized by extremely high levels of methylation in the 5'-region, demethylation of which resulted in activation of Mest. Furthermore, a methylated reporter construct with the luciferase gene under the control of the putative promoter region of Mest was not competent to produce luciferase activity in MC12 cells. These results suggest a suppressive role for DNA methylation in Mest expression. However, neither methylated nor unmethylated reporter constructs showed luciferase activity in a primary culture from the adult kidney, in which Mest is down-regulated despite apparent unmethylation of the paternal allele. Taken together, the data suggest that there are probably two modes of regulation for the Mest gene; one being a methylation-dependent mechanism that regulates imprinted expression of Mest during development, and the other being a methylation-independent mechanism that is involved in down-regulation of Mest in adult tissues.

Abnormal maternal behaviour and growth retardation associated with loss of the imprinted gene Mest

Mest (also known as Peg1), an imprinted gene expressed only from the paternal allele during development, was disrupted by gene targeting in embryonic stem (ES) cells. The targeted mutation is imprinted and reversibly silenced by passage through the female germ line. Paternal transmission activates the targeted allele and causes embryonic growth retardation associated with reduced postnatal survival rates in mutant progeny. More significantly, Mest-deficient females show abnormal maternal behaviour and impaired placentophagia, a distinctive mammalian behaviour. Our results provide evidence for the involvement of an imprinted gene in the control of adult behaviour.

Disruption of primary imprinting during oocyte growth leads to the modified expression of imprinted genes during embryogenesis

Parthenogenetic embryos, which contained one genome from a neonate-derived non-growing oocyte and the other from a fully grown oocyte, developed to day 13.5 of gestation in mice, 3 days longer than previously recorded for parthenogenetic development. To investigate the hypothesis that disruption of primary imprinting during oocyte growth leads to the modified expression of imprinted genes and this parthenogenetic phenotype, we have examined Peg1/Mest, Igf2, Peg3, Snrpn, H19, Igf2r and excess p57KIP2. We show that paternally expressed genes, Peg1/Mest, Peg3 and Snrpn, are expressed in the parthenotes, presumably due to a lack of maternal epigenetic modifications during oocyte growth. In contrast, the expression of Igf2, which is repressed in a competitive manner by transcription of the H19 gene, was very low. Furthermore, we show that the maternally expressed Igf2r and p57KIP2 genes were repressed in the alleles of the non-growing oocyte indicating maternal modifications during oocyte growth are necessary for its expression. Thus, our results show that primary imprinting during oocyte growth exhibits a crucial effect on both the expression and repression of maternal alleles during embryogenesis.

Genomic structure and parent-of-origin-specific methylation of Peg1

We previously identified Peg1/Mest as a novel paternally expressed gene in the developing mouse embryo. The human PEG1 gene was recently assigned to 7q32 and shown to be imprinted and paternally expressed. Therefore, PEG1 deficiency could participate in the aetiology of pre- and post-natal growth retardation associated with maternal uniparental disomy 7 in humans. We have now initiated the characterization of the Peg1 locus in order to identify and dissect cis-acting elements implicated in its imprinted monoallelic expression. The genomic structure of Peg1 as well as the DNA sequence of the 5'-end of the gene, including 2.4 kb of promoter sequences and covering the first 2 exons, have been determined. Important sequence elements, such as a CpG island spanning exon 1 and direct repeats, are identified and discussed. To address the role of epigenetic modifications in the imprinting of Peg1, a methylation analysis of the Peg1 gene is presented. Partially methylated cytosine residues in 13.5 d.p.c. embryos and undifferentiated ES cells were identified. Using embryos carrying a targetted mutation at the Peg1 locus, we show that this partial promoter methylation pattern reflects a strict parent-of-origin-specific differential methylation: the expressed paternal allele is unmethylated, whereas the silenced maternal allele is fully methylated at the CpG sites studied. That the gametes carry the epigenetic information necessary to lay down this allele-specific methylation pattern is suggested by analysis of DNA isolated from sperm and parthenogenetic embryos.

Monoallelic expression of human PEG1/MEST is paralleled by parent-specific methylation in fetuses

We have isolated the human PEG1/MEST gene and have investigated its imprinting status and parental-specific methylation. FISH mapping assigned the gene to chromosome 7q32, and homologous sequences were identified on the short arm of human chromosomes 3 and 5. Through the use of a newly identified intragenic polymorphism, expression analysis revealed that PEG1/MEST is monoallelically transcribed in all fetal tissues examined. In two informative cases, expression was shown to be confined to the paternally derived allele. In contrast to the monoallelic expression observed in fetal tissues, biallelic expression was evident in adult blood lymphocytes. Biallelic expression in blood is supported by the demonstration of PEG1/MEST transcripts in a lymphoblastoid cell line with maternal uniparental disomy 7. The human PEG1/MEST gene spans a genomic region of approximately 13 kb. Sequence analysis of the 5' region of PEG1/MEST revealed the existence of a 620-bp-long CpG island that extends from the putative promoter region into intron 1. We demonstrate that this CpG island is methylated in a parent-of-origin-specific manner. All MspI/HpaII sites were unmethylated on the active paternal allele but methylated on the inactive maternal one.

Representational difference analysis of cDNA of genes expressed in embryonic kidney

Representational difference analysis of cDNA (cDNA-RDA) is a PCR-based differential cloning method. It involves hybridization of two populations of cDNA with selective amplification of differentially expressed genes. To isolate the differentially expressed genes during renal development, mRNAs from embryonic kidneys at day 13 (E13) and postnatal kidneys from three-week-old (P3) mice were extracted, and double stranded cDNAs prepared. Double stranded cDNAs were digested with DpnII, adaptor-ligated, and amplified by PCR, using adaptor primer to generate "representative amplicons." These reflect the "representation" of most of the cDNA population. The term "amplicons" denotes amplified PCR product. Among the two populations of cDNA, E13 kidney cDNA was used as a "tester," containing target genes, and P3 kidney cDNA as a "driver," driving the process of subtraction, following which, they were subjected to cDNA-RDA under low stringency conditions. During the first round of cDNA-RDA embryonic globin genes were isolated. To competitively eliminate these genes, plasmid DNAs of globin genes were supplemented into driver, and subjected to the second round of cDNA-RDA. This resulted in the isolation of four cDNA clones: H19 gene, mesoderm-specific cDNA, COL2A1 gene, and a novel cDNA. By Northern blot analyses, the H19 gene and mesoderm-specific cDNA exhibited a high degree of developmental regulation, that is, they were abundantly expressed in E13 kidney, and their expression was barely detectable in P3 kidney. The differential developmental regulation of mesoderm-specific cDNA was confirmed by tissue in situ hybridization experiments. The COL2A1 and novel cDNA were rare transcripts in the embryonic Kidney. However, Southern blot analyses of representations indicated their up-regulated expressions in E13 kidneys. The novel gene was differentially expressed in 13-day embryonic lung, and Northern blot analysis revealed an approximately 10 Kb transcript. These results indicate that cDNA-RDA is a sensitive technique to identify rare transcripts with differential expression, and since there is a minimal chance to isolate false positive clones, cDNA-RDA may serve as a powerful tool for delineating up- or down-regulation of the genes involved in various pathological or physiological states of the kidney.

Human PEG1/MEST, an imprinted gene on chromosome 7

The mouse Peg1/Mest gene is an imprinted gene that is expressed particularly in mesodermal tissues in early embryonic stages. It was the most abundant imprinted gene among eight paternally expressed genes (Peg 1-8) isolated by a subtraction-hybridization method from a mouse embryonal cDNA library. It has been mapped to proximal mouse chromosome 6, maternal duplication of which causes early embryonic lethality. The human chromosomal region that shares syntenic homology with this is 7q21-qter, and human maternal uniparental disomy 7 (UPD 7) causes apparent growth deficiency and slight morphological abnormalities. Therefore, at least one paternally expressed imprinted gene seems to be present in this region. In this report, we demonstrate that human PEG1/MEST is an imprinted gene expressed from a paternal allele and located on chromosome 7q31-34, near D7S649. It is the first imprinted gene mapped to human chromosome 7 and a candidate for a gene responsible for primordial growth retardation including Silver-Russell syndrome (SRS).

Peg1/Mest imprinted gene on chromosome 6 identified by cDNA subtraction hybridization

Parthenogenesis in the mouse is embryonic lethal partly because of imprinted genes that are expressed only from the paternal genome. In a systematic screen using subtraction hybridization between cDNAs from normal and parthenogenetic embryos, we initially identified two apparently novel imprinted genes, Peg1 and Peg3. Peg1 (paternally expressed gene 1) or Mest, the first imprinted gene found on the mouse chromosome 6, may contribute to the lethality of parthenogenones and of embryos with a maternal duplication for the proximal chromosome 6. Peg1/Mest is widely expressed in mesodermal tissues and belongs to the alpha/beta hydrolase fold family. A similar approach with androgenones can be used to identify imprinted genes that are expressed from the maternal genome only.