Biomedical subjects

J A Yoder

Publications and source records attributed to J A Yoder.

26 records · Page 2Linked to original sources

PubMed1998

Sex-specific exons control DNA methyltransferase in mammalian germ cells.

The spermatozoon and oocyte genomes bear sex-specific methylation patterns that are established during gametogenesis and are required for the allele-specific expression of imprinted genes in somatic tissues. The mRNA for Dnmt1, the predominant maintenance and de novo DNA (cytosine-5)-methyl transferase in mammals, is present at high levels in postmitotic murine germ cells but undergoes alternative splicing of sex-specific 5' exons, which controls the production and localization of enzyme during specific stages of gametogenesis. An oocyte-specific 5' exon is associated with the production of very large amounts of active Dnmt1 protein, which is truncated at the N terminus and sequestered in the cytoplasm during the later stages of oocyte growth, while a spermatocyte-specific 5' exon interferes with translation and prevents production of Dnmt1 during the prolonged crossing-over stage of male meiosis. During the course of postnatal oogenesis, Dnmt1 is present at high levels in nuclei only in growing dictyate oocytes, a stage during which gynogenetic developmental potential is lost and biparental developmental potential is gained.

Alternative Splicing↗

PubMed1997

DNA (cytosine-5)-methyltransferases in mouse cells and tissues. Studies with a mechanism-based probe.

The mechanisms that establish and maintain methylation patterns in the mammalian genome are very poorly understood, even though perturbations of methylation patterns lead to a loss of genomic imprinting, ectopic X chromosome inactivation, and death of mammalian embryos. A family of sequence-specific DNA methyltransferases has been proposed to be responsible for the wave of de novo methylation that occurs in the early embryo, although no such enzyme has been identified. A universal mechanism-based probe for DNA (cytosine-5)-methyltransferases was used to screen tissues and cell types known to be active in de novo methylation for new species of DNA methyltransferase. All identifiable de novo methyltransferase activity was found to reside in Dnmt1. As this enzyme is the predominant de novo methyltransferase at all developmental stages inspected, it does not fit the definition of maintenance methyltransferase or hemimethylase. Recent genetic data indicate that de novo methylation of retroviral DNA in embryonic stem cells is likely to involve one or more additional DNA methyltransferases. Such enzymes were not detected and are either present in very small amounts or are very different from Dnmt1. A new method was developed and used to determine the sequence specificity of intact Dnmt1 in whole-cell lysates. Specificity was found to be confined to the sequence 5'-CpG-3'; there was little dependence on sequence context or density of CpG dinucleotides. These data suggest that any sequence-specific de novo methylation mediated by Dnmt1 is either under the control of regulatory factors that interact with Dnmt1, or is cued by alternative secondary structures in DNA.

Amino Acid Sequence↗

PubMed1997

Cytosine methylation and the ecology of intragenomic parasites.

Most of the 5-methylcytosine in mammalian DNA resides in transposons, which are specialized intragenomic parasites that represent at least 35% of the genome. Transposon promoters are inactive when methylated and, over time, C-->T transition mutations at methylated sites destroy many transposons. Apart from that subset of genes subject to X inactivation and genomic imprinting, no cellular gene in a non-expressing tissue has been proven to be methylated in a pattern that prevents transcription. It has become increasingly difficult to hold that reversible promoter methylation is commonly involved in developmental gene control; instead, suppression of parasitic sequence elements appears to be the primary function of cytosine methylation, with crucial secondary roles in allele-specific gene expression as seen in X inactivation and genomic imprinting.

Animals↗

PubMed1997

Awareness of deficit in Alzheimer's disease: relation to caregiver burden.

Patients with Alzheimer's disease (AD) show varying degrees of awareness of their deficits. To examine the impact of this phenomenon upon the distress experienced by family caregivers of AD patients, we analyzed caregiver burden in relation to patient awareness of deficit in three different functional domains. The relationship of burden to selected sociodemographic variables was also explored. Results of multiple regression analyses suggested that caregiver burden was associated with impaired patient awareness of memory deficit independent of disease stage and dementia severity. The findings suggest that impaired awareness may be an important mediator of caregiver burden, a concern in the management of AD.

Activities of Daily Living↗

PubMed1997

Elective laparoscopic splenectomy for hematologic disorders.

Laparoscopic splenectomy has been reported to be the procedure of choice in selected patients with hematologic disorders. The purpose of this study is to review our experience with laparoscopic splenectomy in this patient population. The charts of all patients with hematologic disorders who presented for laparoscopic splenectomy over a 17-month period were reviewed. Fifteen patients, nine males and six females, aged 12 to 80 years (mean, 49 years) presented for laparoscopic splenectomy. Surgical indications included 13 cases of idiopathic thrombocytopenic purpura and one each of hemolytic anemia and Hodgkin's disease. Splenectomy was performed utilizing a four- or five-puncture laparoscopic technique. For completed laparoscopic splenectomies, the mean operative time was 129 minutes, and the mean estimated blood loss was 232 cc. Mean splenic weight was 210 g. There were no operative deaths. There was a single intraoperative complication, a 1700-cc hemorrhage, and two postoperative complications: pneumonitis and deep venous thrombosis. Overall morbidity was 20 per cent. A single patient (7%) required conversion to laparotomy for completion due to hemorrhage. For patients completed laparoscopically, the mean hospitalization was 1.5 days, and none required parenteral narcotics for pain control after the first 36 hours. Laparoscopic splenectomy for patients with hematologic disorders is a safe and technically feasible procedure. Decreased hospitalization and discomfort are the primary benefits. This technique should be added to the repertoire of surgeons treating patients with hematologic disorders.

Adolescent↗

PubMed1996

New 5' regions of the murine and human genes for DNA (cytosine-5)-methyltransferase.

DNA (cytosine-5)-methyltransferases (EC 2.1.1.37) maintain patterns of methylated cytosine residues in the mammalian genome; faithful maintenance of methylation patterns is required for normal development of mice, and aberrant methylation patterns are associated with certain human tumors and developmental abnormalities. The organization of coding sequences at the 5'-end of the murine and human DNA methyltransferase genes was investigated, and the DNA methyltransferase open reading frame was found to be longer than previously suspected. Expression of the complete open reading frame by in vitro transcription-translation and by transfection of expression constructs into COS7 cells resulted in the production of an active DNA methyltransferase of the same apparent mass as the endogenous protein, while translation from the second in-frame ATG codon produced a slightly smaller but fully active protein. Characterization of mRNA 5' sequences and the intron-exon structure of the 5' region of the murine and human genes indicated that a previously described promoter element (Rouleau, J., Tanigawa, G., and Szyf, M. (1992) J. Biol. Chem. 267, 7368-7377) actually lies in an intron that is more than 5 kilobases downstream of the transcription start sites.

Amino Acid Sequence↗

PubMed1996

Genetic analysis of genomic methylation patterns in plants and mammals.

While it is now accepted that methylation of cytosine residues plays a role in various epigenetic phenomena in mammals and flowering plants, the involvement of methylation patterns in the regulation of normal development has remained a controversial and essentially untested issue in the 20 years since such a role was first proposed. Antisense suppression of a DNA methyltransferase in Arabidopsis and characterization of methylation-defective mutants of Arabidopsis have shown that perturbations of methylation patterns disrupt the development of plants, and targeted mutation of the murine gene that encodes the one known from of DNA methyltransferase has shown that methylation is required for cellular differentiation, genomic imprinting, and X chromosome inactivation in mammals. Ectopic expression of homeotic genes and homeotic transformations of floral organs in methylation-defective plants suggest that (in plants and perhaps mammals) heritable methylation patterns reinforce and may have supplanted heritable gene control mediated by chromosomal proteins of the Polycomb and trithorax groups. It is also possible that the developmental abnormalities are the result of ectopic gene expression caused by activation of transcription from nearby parasitic sequence elements that are normally repressed by methylation. Application of modern methods of genetic analysis promises to give definite answers to long-standing questions as to the roles and significance of genomic methylation patterns in normal development and genome defense.

Animals↗

PubMed1991

Cross-linking a maturation-dependent ram sperm plasma membrane antigen induces the acrosome reaction.

ESA152 is a highly hydrophobic 18 kDa sialoglycoprotein, which becomes expressed on ram sperm in the proximal cauda epididymis. ESA 152 is expressed on all regions of the sperm surface, most strongly on the posterior region of the head, most weakly on the anterior region of the head. In this paper, we show that induction of the acrosome reaction with Ca2+ ionophore causes ESA152 to be redistributed from the posterior to the anterior region of the head plasma membrane. Cross-linking ESA152 with bivalent antibody causes similar redistribution and induces the acrosome reaction. Induction of the acrosome reaction with ESA152 antibody requires Ca2+ but is insensitive to (10 ng/ml) pertussis toxin.

Acrosome↗