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M A Surani

Publications and source records attributed to M A Surani.

At least 19 recordsLinked to original sources
PubMed2003

The fragilis interferon-inducible gene family of transmembrane proteins is associated with germ cell specification in mice.

BACKGROUND: Specification of primordial germ cells in mice depends on instructive signalling events, which act first to confer germ cell competence on epiblast cells, and second, to impose a germ cell fate upon competent precursors. fragilis, an interferon-inducible gene coding for a transmembrane protein, is the first gene to be implicated in the acquisition of germ cell competence. RESULTS: Here, we describe four additional fragilis-related genes, fragilis2-5, which are clustered within a 68 kb region in the vicinity of the fragilis locus on Chr 7. These genes exist in a number of mammalian species, which in the human are also clustered on the syntenic region on Chr 11. In the mouse, fragilis2 and fragilis3, which are proximate to fragilis, exhibit expression that overlaps with the latter in the region of specification of primordial germ cells. Using single cell analysis, we confirm that all these three fragilis-related genes are predominant in nascent primordial germ cells, as well as in gonadal germ cells. CONCLUSION: The Fragilis family of interferon-inducible genes is tightly associated with germ cell specification in mice. Furthermore, its evolutionary conservation suggests that it probably plays a critical role in all mammals. Detailed analysis of these genes may also elucidate the role of interferons as signalling molecules during development.

Amino Acid Sequence↗
PubMed2001

Genome-wide methylation patterns in normal and uniparental early mouse embryos.

In the normal diploid mouse embryo, active demethylation of the paternal genome but not of the maternal genome occurs within only a few hours and in a highly coordinated fashion as the zygote proceeds through the first G1 phase. This zygotic demethylation may be necessary to reprogram the sperm genome for somatic development. Immunofluorescence staining with an antibody against 5-methylcytosine shows that the cellular machinery of the fertilized egg cannot demethylate the second maternal genome in parthenogenetic, gynogenetic and triploid digynic embryos or remethylate the additional (already demethylated) paternal genome in androgenetic and triploid diandric embryos. This suggests that differential zygotic demethylation results from differences in the remodeling of paternal and maternal chromatin structures after fertilization, i.e. sperm nuclear decondensation and protamine-histone exchange. A proportion of embryos derived from normal matings display abnormal methylation patterns some of which are indistinguishable from those in androgenetic or gynogenetic embryos. We conclude that methylation reprogramming defects in mammalian zygotes contribute to the high incidence of early pregnancy failure.

Animals↗
PubMed2001

Reprogramming of genome function through epigenetic inheritance.

Most cells contain the same set of genes and yet they are extremely diverse in appearance and functions. It is the selective expression and repression of genes that determines the specific properties of individual cells. Nevertheless, even when fully differentiated, any cell can potentially be reprogrammed back to totipotency, which in turn results in re-differentiation of the full repertoire of adult cells from a single original cell of any kind. Mechanisms that regulate this exceptional genomic plasticity and the state of totipotency are being unravelled, and will enhance our ability to manipulate stem cells for therapeutic purposes.

Animals↗
PubMed2001

Imprinted expression of neuronatin from modified BAC transgenes reveals regulation by distinct and distant enhancers.

Neuronatin (Nnat) is an imprinted gene that is expressed exclusively from the paternal allele while the maternal allele is silent and methylated. The Nnat locus exhibits some unique features compared with other imprinted domains. Unlike the majority of imprinted genes, which are organised in clusters and coordinately regulated, Nnat does not appear to be closely linked to other imprinted genes. Also unusually, Nnat is located within an 8-kb intron of the Bc10 gene, which generates a biallelically expressed, antisense transcript. A similar organisation is conserved at the human NNAT locus on chromosome 20. Nnat expression is first detected at E8.5 in rhombomeres 3 and 5, and subsequently, expression is widespread within postmitotic neuronal tissues. Using modified BAC transgenes, we show that imprinted expression of Nnat at ectopic sites requires, at most, an 80-kb region around the gene. Furthermore, reporter transgenes reveal distinct and dispersed cis-regulatory elements that direct tissue-specific expression and these are predominantly upstream of the region that confers allele-specific expression.

Alleles↗
PubMed2001

Imprinting and the epigenetic asymmetry between parental genomes.

Genomic imprinting confers a developmental asymmetry on the parental genomes, through epigenetic modifications in the germ line and embryo. These heritable modifications regulate the monoallelic activity of parental alleles resulting in their functional differences during development. Specific cis-acting regulatory elements associated with imprinted genes carry modifications involving chromatin structural changes and DNA methylation. Some of these modifications are initiated in the germ line. Comparative genomic analysis at imprinted domains is emerging as a powerful tool for the identification of conserved elements amenable to more detailed functional analysis, and for providing insight into the emergence of imprinting during the evolution of mammalian species. Genomic imprinting therefore provides a model system for the analysis of the epigenetic control of genome function.

Alleles↗
PubMed2001

Loss of Xist imprinting in diploid parthenogenetic preimplantation embryos.

We have analysed Xist expression patterns in parthenogenetic and control fertilised preimplantation embryos by using RNA FISH. In normal XX embryos, maternally derived Xist alleles are repressed throughout preimplantation development. Paternal alleles are expressed as early as the 2-cell stage. In parthenogenetic embryos, we observed Xist RNA expression and accumulation from the morula stage onwards, indicating loss of maternal imprinting. In the majority of cells, expression was from a single allele, indicating that X chromosome counting occurs to establish appropriate monoallelic Xist expression. We discuss these data in the context of models for regulation of imprinted and random X inactivation.

Alleles↗
PubMed2001

Distant cis-elements regulate imprinted expression of the mouse p57( Kip2) (Cdkn1c) gene: implications for the human disorder, Beckwith--Wiedemann syndrome.

Complex phenotypes and genotypes characterize the human disease, Beckwith--Wiedemann syndrome (BWS). Genetic and epigenetic mutations are found in five different genes which all lie within a 1 Mb imprinted domain on human chromosome 11p15. Only two of these genes, p57(KIP2) (CDKN1C) and IGF2, are likely to be functionally involved in this disease. The presence of the additional mutations therefore suggests a role for the regulation of these two genes by distant cis-elements. The mouse Igf2 gene is regulated by enhancers and imprinting elements which lie >120 kb downstream of its promoter. Here we show that key elements for expression of the mouse p57(Kip2) (Cdkn1c) gene also lie at a distance. Enhancers for expression within skeletal muscle and cartilage lie >25 kb downstream of the gene. In addition, we find no evidence for allele-specific expression of p57(Kip2) (Cdkn1c) from our bacterial artificial chromosome transgenes that span 315 kb around the locus. This suggests that a key imprinting element for p57(Kip2) (Cdkn1c) also lies at a distance. Therefore, BWS in humans may result from disruption of appropriate expression of the p57(KIP2) (CDKN1C) gene through mutations that occur at a substantial distance from the gene.

Animals↗
PubMed2001

A conserved imprinting control region at the HYMAI/ZAC domain is implicated in transient neonatal diabetes mellitus.

Transient neonatal diabetes mellitus (TNDM) is associated with intra-uterine growth retardation, dehydration and a lack of insulin. Some TNDM patients exhibit paternal uniparental disomy (UPD) of chromosome 6q24, where at least two imprinted genes, HYMAI and ZAC, have so far been characterized. Here we show that the differentially methylated CpG island that partially overlaps mZac1 and mHymai at the syntenic mouse locus is a likely imprinting control region (ICR) for the approximately 120--200 kb domain. The region is unmethylated in sperm but probably methylated in oocytes, a difference that persists between parental alleles throughout pre- and post-implantation development. We also show that within this ICR, there is a region that exhibits a high degree of homology between mouse and human. Using a reporter expression assay, we demonstrate that this conserved region acts as a strong transcriptional repressor when methylated. Finally, we provide in vivo evidence that in the majority of TNDM patients with a normal karyotype, there is a loss of methylation within the highly homologous region. We propose that this ICR regulates expression of imprinted genes within the domain; epigenetic or genetic mutations of this region probably result in TNDM, possibly by affecting expression of ZAC in the pancreas and/or the pituitary.

Alleles↗
PubMed2001

Paternal monoallelic expression of PEG3 in the human placenta.

Genomic imprinting is the phenomenon whereby mono-allelic expression of certain genes occurs depending on their parental origin. The observation that imprinting only occurs in placental mammals has led to the suggestion that it may play a role in this form of reproduction. In the present study we have investigated the pattern of expression of the human PEG3 gene in the early to term placenta, as well as the uterus and ovary, using RT-PCR, northern blot and in situ hybridization. A comparison is made with the expression of Peg3 in the mouse by histochemical staining in betageo knock out mice. We have demonstrated high levels of PEG3 in the human placenta and have localized the signal to the layer of villous cytotrophoblast cells. In contrast, the pattern of expression of Peg3 in the mouse placenta is less restricted, the message being present in all trophoblast populations. Thus, expression of PEG3/Peg3 in the human and mouse placenta is not directly comparable. We have also detected PEG3 message in the ovarian stroma. We have sequenced the human PEG3 gene from exon 3 to exon 9. By utilizing a polymorphism detected in exon 9, we have established that only the paternal allele is expressed in human placenta. Human PEG3 is therefore maternally imprinted as in mouse.

Amino Acid Sequence↗
PubMed2001

The polycomb-group gene Ezh2 is required for early mouse development.

Polycomb-group (Pc-G) genes are required for the stable repression of the homeotic selector genes and other developmentally regulated genes, presumably through the modulation of chromatin domains. Among the Drosophila Pc-G genes, Enhancer of zeste [E(z)] merits special consideration since it represents one of the Pc-G genes most conserved through evolution. In addition, the E(Z) protein family contains the SET domain, which has recently been linked with histone methyltransferase (HMTase) activity. Although E(Z)-related proteins have not (yet) been directly associated with HMTase activity, mammalian Ezh2 is a member of a histone deacetylase complex. To investigate its in vivo function, we generated mice deficient for Ezh2. The Ezh2 null mutation results in lethality at early stages of mouse development. Ezh2 mutant mice either cease developing after implantation or initiate but fail to complete gastrulation. Moreover, Ezh2-deficient blastocysts display an impaired potential for outgrowth, preventing the establishment of Ezh2-null embryonic stem cells. Interestingly, Ezh2 is up-regulated upon fertilization and remains highly expressed at the preimplantation stages of mouse development. Together, these data suggest an essential role for Ezh2 during early mouse development and genetically link Ezh2 with eed and YY1, the only other early-acting Pc-G genes.

Animals↗
PubMed2001

Epigenetic reprogramming of the genome--from the germ line to the embryo and back again.

Mammalian parental genomes are not functionally equivalent, and both a maternal and paternal contribution is required for normal development. The differences between the parental genomes are the result of genomic imprinting--a form of gene regulation that results in monoallelic expression of imprinted genes. Cis-regulatory elements at imprinted loci are responsible for directing allele-specific epigenetic marks required for correct gene expression. This cis information must be interpreted at various points in development, including in the germline where existing imprints are erased and reset. Imprints must also be maintained during preimplantation development, when the genome undergoes dramatic global epigenetic changes.

Animals↗
PubMed2000

A novel imprinted gene, HYMAI, is located within an imprinted domain on human chromosome 6 containing ZAC.

Transient neonatal diabetes mellitus (TNDM) is a rare disease characterized by intrauterine growth retardation, dehydration, and failure to thrive due to a lack of normal insulin secretion. This disease is associated with paternal uniparental disomy or paternal duplication of chromosome 6, suggesting that the causative gene(s) for TNDM is imprinted. Recently, Gardner et al. (1999, J. Med. Genet. 36: 192-196) proposed that a candidate gene for TNDM lies within chromosome 6q24.1-q24.3. To find human imprinted genes, we performed a database search for EST sequences that mapped to this region, followed by RT-PCR analysis using monochromosomal hybrid cells with a human chromosome 6 of defined parental origin. Here we report the identification of a novel imprinted gene, HYMAI. This gene exhibits differential DNA methylation between the two parental alleles at an adjacent CpG island and is expressed only from the paternal chromosome. A previously characterized imprinted gene, ZAC/LOT1, is located 70 kb downstream of HYMAI and is also expressed only from the paternal allele. In the pancreas, both genes are moderately expressed. HYMAI and ZAC/LOT1 are therefore candidate genes involved in TNDM. Furthermore, the human chromosome 6q24 region is syntenic to mouse chromosome 10 and represents a novel imprinted domain.

Alleles↗
PubMed2000

Ocat, a paternally expressed gene closely linked and transcribed in the opposite direction to Peg3.

Two reciprocally imprinted Kruppel-type zinc finger genes, Peg3 and Zim1, have been found in close proximity on mouse proximal chromosome 7. Here, we describe the identification of another novel imprinted transcript, Ocat (ossification center-associated transcript). Ocat encodes a 5.5-kb spliced transcript and is transcribed in the opposite orientation to Peg3. One of its exons (putative exon 1) lies approximately 200 bp upstream of Peg3. Ocat is predominantly expressed in embryos from days 11 to 17, particularly in ossification centers of the embryonic skeleton at day 15. Like Peg3, Ocat is expressed exclusively from the paternal allele. Despite their proximity, Peg3 and Ocat showed dissimilar expression profiles, suggesting that they are regulated by independent genetic elements.

Animals↗
PubMed2000

Eomesodermin is required for mouse trophoblast development and mesoderm formation.

The earliest cell fate decision in the mammalian embryo separates the extra-embryonic trophoblast lineage, which forms the fetal portion of the placenta, from the embryonic cell lineages. The body plan of the embryo proper is established only later at gastrulation, when the pluripotent epiblast gives rise to the germ layers ectoderm, mesoderm and endoderm. Here we show that the T-box gene Eomesodermin performs essential functions in both trophoblast development and gastrulation. Mouse embryos lacking Eomesodermin arrest at the blastocyst stage. Mutant trophoectoderm does not differentiate into trophoblast, indicating that Eomesodermin may be required for the development of trophoblast stem cells. In the embryo proper, Eomesodermin is essential for mesoderm formation. Although the specification of the anterior-posterior axis and the initial response to mesoderm-inducing signals is intact in mutant epiblasts, the prospective mesodermal cells are not recruited into the primitive streak. Our results indicate that Eomesodermin defines a conserved molecular pathway controlling the morphogenetic movements of germ layer formation and has acquired a new function in mammals in the differentiation of trophoblast.

Amino Acid Sequence↗
PubMed2000

Appropriate expression of the mouse H19 gene utilises three or more distinct enhancer regions spread over more than 130 kb.

H19 and Igf2 are closely linked, reciprocally imprinted genes which lie on distal chromosome 7 in the mouse. Data suggests that common elements are used for expression and imprinting of both genes, and simple models have been proposed based on the presence of a single set of enhancers located downstream of H19. In this study we have investigated the H19 expression pattern from a 130 kb YAC transgene, which imprints H19 appropriately at ectopic loci. However, we show that while enhancers for expression in many cell types are present on the YAC, those for expression in mesodermal components of the heart, kidney, lung and thymus are located at a greater distance. Based on the available evidence, we conclude that regulation of H19 is complex, requiring contribution from at least three different sets of cell-type specific enhancers. Thus, the mechanism of reciprocal imprinting of H19 and Igf2 utilises different regulatory elements in different cell types during mouse development.

Animals↗
PubMed2000

Organization and parent-of-origin-specific methylation of imprinted Peg3 gene on mouse proximal chromosome 7.

Peg3 is the first imprinted gene to be identified on mouse proximal chromosome 7; the human PEG3 homologue is on chromosome 19q13.4. Peg3 encodes a C(2)H(2)-type zinc finger protein that is expressed only from the paternal allele in embryos and adult brain. The gene has been shown to regulate maternal behavior and offspring growth and has been implicated in the TNF-NFkappaB signal pathway. Here we show that Peg3 consists of nine exons spanning 26 kb. The 5' region of the gene contains a region rich in repeated sequences and a CpG island. Analysis of expressed sequence tags revealed a transcript present upstream of the island and on the strand opposite to Peg3. These structural features and DNA sequences are conserved in mouse and human. The 5' region of Peg3 is preferentially methylated on the inactive maternal allele, as shown by comparing embryos with paternal (PatDp. prox7) and maternal (MatDp.prox7) duplication of proximal chromosome 7. Recently, a new maternally expressed Zim1 gene located downstream of Peg3 was identified, which suggested that another imprinted cluster is present on proximal chromosome 7.

Animals↗