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Biomedical subjects

Lorraine Young

Publications and source records attributed to Lorraine Young.

7 recordsLinked to original sources
PubMed2005

Human embryonic stem cell methyl cycle enzyme expression: modelling epigenetic programming in assisted reproduction?

To investigate a possible mechanism for inducing epigenetic defects in the preimplantation embryo, a human embryonic stem cell model was developed, and gene expression of the key methyl cycle enzymes, MAT2A, MAT2B, GNMT, SAHH, CBS, CGL, MTR, MTRR, BHMT, BHMT2, mSHMT, cSHMT and MTHFR was demonstrated, while MAT1 was barely detectable. Several potential acceptors of cycle-generated methyl groups, the DNA methyltransferases (DNMT1, DNMT3A, DNMT3B and DNMT3L), glycine methyltransferase and the polyamine biosynthetic enzymes, SAM decarboxylase and ornithine decarboxylase, were also expressed. Expression of folate receptor alpha suggests a propensity for folate metabolism. Methotrexate-induced depletion of folate resulted in elevated intracellular homocysteine concentration after 7 days in culture and a concomitant increase in cysteine and glutathione, indicating clearance of homocysteine through the transulphuration pathway. These studies indicate that altered methyl group metabolism provides a potential mechanism for inducing epigenetic changes in the preimplantation embryo.

Cell Proliferation↗
PubMed2005

Molecular and phenotypic analyses of human embryonic stem cell-derived cardiomyocytes: opportunities and challenges for clinical translation.

Differentiation of human embryonic stem cells (hESCs) into cardiomyocytes in culture may offer unique opportunities for modeling genetic disorders, screening potentially cardiotoxic pharmaceutical agents or replacing cells of the diseased heart. However, before clinical utility can be realized, numerous hurdles must be overcome. Comprehensive molecular and phenotypic characterization is required but has so far been restricted to cardiomyocytes derived from a limited subset of hESC lines. Thus, we have initiated analysis of cardiomyocyte differentiation and function from a further two independently derived lines, BG01 and HUES-7. The challenge of improving cardiac cell induction, enrichment and maturation must also be addressed to meet the demands of high throughput pharmaceutical screening or to provide sufficient cells to repair an infarcted heart. Transplanted cells must functionally integrate without inducing arrhythmias, while survival and evasion of immune surveillance must be accomplished without tumorigenicity. This review evaluates the opportunities presented by hESC-derived cardiomyocytes and the progress towards surmounting the challenges of clinical translation.

Cell Differentiation↗
PubMed2005

Epigenetics and the germline.

Epigenetic processes affect three stages of germline development, namely (1) specification and formation of primordial germ cells and their germline derivatives through lineage-specific epigenetic modifications, in the same manner as other embryonic lineages are formed, (2) a largely genome-wide erasure and re-establishment of germline-specific epigenetic modifications that only occurs in the embryonic primordial germ cell lineage, followed by re-establishment of sex-specific patterns during gametogenesis, and (3) differential epigenetic modifications to the mature male and female gamete genomes shortly after fertilisation. This review will detail current knowledge of these three processes both at the genome-wide level and at specific imprinted loci. The consequences of epigenetic perturbation are discussed and new in vitro models which may allow further understanding of a difficult developmental period to study, especially in the human, are highlighted.

Animals↗
PubMed2004

Effect of limited DNA methylation reprogramming in the normal sheep embryo on somatic cell nuclear transfer.

Active demethylation of cytosine residues in the sperm genome before forming a functional zygotic nucleus is thought to be an important function of the oocyte cytoplasm for subsequent embryonic development in the mouse. Conversely, this event does not occur in the sheep or rabbit zygote and occurs only partially in the cow. The aim of this study was to investigate the effect of limited methylation reprogramming in the normal sheep embryo on reprogramming somatic nuclei. Sheep fibroblast somatic nuclei were partially demethylated after electrofusion with recipient sheep oocytes and undergo a stepwise passive loss of DNA methylation during early development, as determined by 5-methylcytosine immunostaining on interphase embryonic nuclei. A similar decrease takes place with in vivo-derived sheep embryos up to the eight-cell stage, although nuclear transfer embryos exhibit a consistently higher level of methylation at each stage. Between the eight-cell and blastocyst stages, DNA methylation levels in nuclear transfer embryos are comparable with those derived in vivo, but the distribution of methylated DNA is abnormal in a high proportion. By correlating DNA methylation with developmental potential at individual stages, our results suggest that somatic nuclei that do not undergo rapid reorganization of their DNA before the first mitosis fail to develop within two to three cell cycles and that the observed methylation defects in early cleavage stages more likely occur as a direct consequence of failed nuclear reorganization than in failed demethylation capacity. However, because only embryos with reorganized chromatin appear to survive the 16-cell and morula stages, failure to demethylate the trophectoderm cells of the blastocyst is likely to directly impact on developmental potential by altering programmed patterns of gene expression in extra-embryonic tissues. Thus, both remodeling of DNA and epigenetic reprogramming appear critical for development of both fertilized and nuclear transfer embryos.

Animals↗
PubMedDate not supplied

Stem-cell consequences of embryo epigenetic defects.

CONTEXT: The genetic code in the DNA of virtually every somatic cell can produce the entire complement of encoded proteins. Acetylation of histones and methylation of histones and DNA cytosine residues are part of the complex epigenetic regulatory process determining lineage-specific gene expression by altering the local structure of chromatin. After fertilisation, sperm DNA exchanges protamines for histones recruited from oocyte cytoplasm, reconfiguring both parental genomes into an epigenetic state conducive to activating the embryonic developmental programme. The identification of epigenetic reprogramming mechanisms is a major interest, rekindled by the ability of at least some somatic cells to acquire totipotency after somatic-cell nuclear transfer. STARTING POINT: Recently, Woo SukHwang and colleagues (Science 2004; 303: 1669-74) derived a human embryonic stem-cell line from embryo therapeutic cloning. Chad Cowan and colleagues (N Engl JMed 2004; 350: 1353-56) produced 17 new lines from embryos supernumerary to infertility treatments. However, increasing evidence from a range of mammals shows a propensity for epigenetic errors with embryo technologies. If paralleled in human embryos, the effect on tumorigenic and differentiation properties of embryonic stem cells needs to be established. WHERE NEXT? Identifying the mechanisms in the oocyte that reprogramme a somatic cell to the embryonic state might allow somatic cells to be reprogrammed ex ovo by in-vitro manipulation of the epigenome. Because the oocyte is designed to reprogramme the sperm genome, which is in a different chromatin state from a somatic cell, perhaps many of the epigenetic errors induced by somatic-cell nuclear transfer could be avoided by a more targeted approach.

Animals↗