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Biomedical subjects

S J Clark

Publications and source records attributed to S J Clark.

At least 73 records · Page 4Linked to original sources
PubMed1999

Impact of North Carolina's universal vaccine purchase program by children's insurance status.

OBJECTIVE: To examine the impact of a new universal purchase vaccine program on immunization rates of children with different types of insurance. DESIGN: Ecologic study using parent telephone interviews, medical chart abstraction in sites of outpatient care, and insurance verification with Medicaid and private insurers. SETTING: State of North Carolina. PARTICIPANTS: Of a random birth certificate sample of 4385 children born in North Carolina during 1994 and 1995, 507 were excluded. A total of 2767 children had completed parent interviews; 95% of those had medical chart abstraction and insurance data. MAIN OUTCOME MEASURES: Immunization rates at each month during the first 2 years of age, site of delivery for immunizations and well-child visits, and insurance status. RESULTS: In month-by-month comparisons, children born in 1995 had immunization rates 4% to 10% higher than their 1994 counterparts. By 24 months of age, 84% of the 1995 cohort had completed the primary immunization series, compared with 79% of the 1994 cohort (P<.001). In all insurance subgroups, 1995 immunization rates were higher than 1994 rates. The largest increases occurred among privately insured children with no well-child coverage, children who had periods of being uninsured, and children enrolled in Medicaid exclusively or with private insurance. More children in the 1995 cohort received immunizations in the private sector. CONCLUSIONS: Implementation of North Carolina's universal purchase program was associated with improved immunization rates, especially for children with inadequate insurance for well-child care. However, insurance status still influences the ability of children to receive immunizations on schedule.

Adolescent↗
PubMed1999

Predatory behaviour of trapping fungi against srf mutants of Caenorhabditis elegans and different plant and animal parasitic nematodes.

The initial infection process of nematode-trapping fungi is based on an interaction between the trapping structure of the fungus and the surface of the nematode cuticle. A bioassay was designed to investigate the predatory response of several isolates of nematode-trapping fungi against 3 mutants of Caenorhabditis elegans (AT6, AT10 and CL261), which have been reported to differ in the reaction of their cuticle to antibodies and lectins. The bioassay was also applied to infective larvae of animal (Haemonchus contortus, Teladorsagia (Ostertagia) circumcincta and Trichostrongylus axei) and plant (Meloidogyne spp.) parasitic nematodes. Differences in trapping ability were most marked in the first 24 h, and were density dependent. Although the isolate of Arthrobotrys responded very rapidly in the first 24 h, Duddingtonia flagrans was generally the most effective isolate and Monacrosporium responded relatively poorly throughout all experiments. All the fungi tested trapped the srf mutants of C. elegans more efficiently than the wild type, and there were differences between the different srf mutants of C. elegans. Differences in trapping ability were also observed between different isolates of D. flagrans; similarly, differences in trapping behaviour were observed not only amongst the different species of plant-parasitic nematodes, but also between the sheathed and exsheathed larvae of the animal-parasitic nematodes.

Animal Population Groups↗
PubMed1999

Cancer-specific region of hypermethylation identified within the HIC1 putative tumour suppressor gene in acute myeloid leukaemia.

Abnormal DNA methylation has been found to be a common feature in cancer cells, although the mechanism of this alteration remains poorly understood. HIC1 is a putative tumour suppressor gene on chromosome 17p13.3 and is hypermethylated in a number of cancers including leukaemia. In this study, using bisulphite genomic sequencing, we have identified a 'boundary' sequence within the HIC1 CpG island that shows a marked junction between methylated and unmethylated DNA in normal haematopoietic cells. Surprisingly, this boundary of differential methylation lies exactly between the intron 2 and exon 3 junction. In contrast to normal haematopoietic cells, hypermethylation extends past this boundary at a high frequency (83%) in newly diagnosed acute myeloid leukaemias (AML). Identification of the hypermethylated boundary sequence not only provides the first step in understanding the mechanisms that normally protect CpG islands from de novo methylation but also may prove to be a useful cancer-specific marker.

Acute Disease↗
PubMed1999

DNA methylation profile of the mouse skeletal alpha-actin promoter during development and differentiation.

Genomic levels of DNA methylation undergo widespread alterations in early embryonic development. However, changes in embryonic methylation have proven difficult to study at the level of single-copy genes due to the small amount of tissue available for assay. This study provides the first detailed analysis of the methylation state of a tissue-specific gene through early development and differentiation. Using bisulfite sequencing, we mapped the methylation profile of the tissue-specific mouse skeletal alpha-actin promoter at all stages of development, from gametes to postimplantation embryos. We show that the alpha-actin promoter, which is fully methylated in the sperm and essentially unmethylated in the oocyte, undergoes a general demethylation from morula to blastocyst stages, although the blastula is not completely demethylated. Remethylation of the alpha-actin promoter occurs after implantation in a stochastic pattern, with some molecules being extensively methylated and others sparsely methylated. Moreover, we demonstrate that tissue-specific expression of the skeletal alpha-actin gene in the adult mouse does not correlate with the methylation state of the promoter, as we find a similar low level of methylation in both expressing and one of the two nonexpressing tissues tested. However, a subset of CpG sites within the skeletal alpha-actin promoter are preferentially methylated in liver, a nonexpressing tissue.

Actins↗
PubMed1999

Chronic lung disease and survival in 4 tertiary neonatal units.

AIM: To compare mortality and respiratory morbidity in preterm infants born at 4 United Kingdom centers during 1994 and 1995. METHOD: Collection of CRIB scores, respiratory parameters and mortality rates from unit databases. RESULTS: Mortality in center A was 27% (actual number of deaths 36/135), in center B was 30% (39/130), in center C was 28% (51/182), in center D was 39% (60/156). The rate of chronic lung disease (36 week definition) in center A was 16%, in center B was 12%, in center C was 13%, in center D was 15%. The predicted number of deaths by CRIB scores in center A was 54 (95% confidence intervals 45-63), in center B was 33 (25-41), in center C was 53 (43-63), in center D was 46 (37-56). CONCLUSION: Center A had a lower than predicted mortality. Center D had a higher than predicted mortality. There is an urgent need for a national neonatal database to allow comparison between center and to identify reasons for variation in outcomes.

Birth Weight↗
PubMed1999

The role of state policies and programs in buffering the effects of poverty on children's immunization receipt.

OBJECTIVES: This study assessed the influence of public policies on the immunization status of 2-year old children in the United States. METHODS: Up-to-dateness for the primary immunization series was assessed in a national sample of 8100 children from the 1988 National Maternal and Infant Health Survey and its 1991 Longitudinal Follow-Up. RESULTS: Documented immunization rates of this sample were 33% for poor children and 44% for others. More widespread Medicated coverage was associated with greater likelihood of up-to-dateness among poor children. Up-to-dateness was more likely for poor children with public rather than private sources of routine pediatric care, but all children living in states where most immunizations were delivered in the public sector were less likely to be up to date. Poor children in state with partial vaccine replacement programs were less likely to be up to date than those in free-market purchase states. CONCLUSIONS: While state policies can enhance immunization delivery for poor children, heavy reliance on public sector immunization does not ensure timely receipt of vaccines. Public- and private-sector collaboration is necessary to protect children from vaccine-preventable diseases.

Adult↗
PubMed1999

Influences on the receipt of well-child visits in the first two years of life.

OBJECTIVE: To determine demographic and health care system factors associated with children receiving an adequate number of well-child visits (WCVs). METHODS: Information on 4385 children and their families was obtained via birth certificates, parent interviews, chart review of outpatient sites of care, and insurance records. RESULTS: Only 77% of children received at least five WCVs by age 2. In regression analysis, the factors most strongly associated with children's total number of WCVs were delay in the initiation of prenatal care (odds ratio = 0.6) and receipt of all outpatient care in private physician offices (odds ratio = 4.2 to 5.6). Having an adequate number of WCVs was associated with being up to date for immunizations. CONCLUSIONS: Children of mothers who delay prenatal care are at high risk for not receiving adequate numbers of WCVs. Recognition of this marker can allow for targeted interventions that aim to ensure that children receive appropriate preventive care.

Adolescent↗
PubMed1998

Loss of p16INK4 expression by methylation is associated with lifespan extension of human mammary epithelial cells.

Inactivation of p16INK4 tumor suppressor gene function is frequently observed in breast cancer. We examined p16INK4 expression in human mammary epithelial cell (HMEC) cultures established from four normal donors. Normal HMECs divide a limited number of times before proliferation ceases in a state referred to as selection (or M0). The cell subpopulation that emerges spontaneously from selection undergoes a further limited period of proliferation before senescence. By immunofluorescence and Western blot analysis of four independent cultures, we have shown loss of p16INK4 expression in postselection HMECs. In contrast, p16INK4 was present in both early and late passage fibroblasts from the same individuals. Bisulfite genomic sequencing revealed extensive methylation of the p16INK4 CpG island in post- but not preselection cells. Thus, the extended period of growth observed in postselection HMECs is associated with hypermethylation of the p16INK4 CpG island and loss of p16INK4 expression. Although postselection HMECs are widely considered to be normal, these data indicate that they have sustained an epigenetic alteration.

Breast↗
PubMed1998

Bisulfite sequencing in preimplantation embryos: DNA methylation profile of the upstream region of the mouse imprinted H19 gene.

In this study we describe a modification of the bisulfite genomic sequencing protocol that enables detection of methylation from as few as five diploid cells from preimplantation mouse embryos. We have used bisulfite genomic sequencing to study the methylation profile of the putative imprinting element upstream of the mouse H19 gene at several stages of embryonic development, including fertilized oocytes and two-cell embryos. The methylation of the H19 imprinting element has recently been described extensively for midgestation embryos, but remains poorly characterized for the preimplantation stages of development, despite widespread changes in genomic DNA methylation occurring at this time. We studied the methylation profile of 35 CpG sites spanning two regions within the H19 imprinting element and found that an overall pattern of allele-specific methylation was maintained at all developmental stages examined, including fertilized oocytes and two-cell embryos. However, allele-specific methylation was not maintained in an absolute fashion subsequent to the first cell division, with a clear flux between partial de novo methylation of the maternal allele and partial demethylation of the paternal allele. Our findings highlight the dynamics of methylation in the early embryo and suggest that it is the overall level of methylation that is responsible for maintenance of the imprinting element and not the methylation of individual CpG sites.

Alleles↗
PubMed1998

Use of public immunization services after initiation of a universal vaccine purchase program.

OBJECTIVE: To explore the reasons why North Carolina families continue to use public immunization services 2 years after implementation of a universal vaccine purchase program, a state program intended to eliminate financial barriers to immunization in private physicians' offices. METHODS: In-person interviews were conducted in 11 local public health departments in North Carolina. PARTICIPANTS: Consecutive sample of 64 adults accompanying children aged 2 years or younger presenting for immunization services. MAIN OUTCOME MEASURES: (1) Reasons for seeking immunization at the health department and (2) history of immunization from private physicians. RESULTS: Two thirds of children obtained immunizations at the health department because of cost, including two thirds of children enrolled in Medicaid. Only 33% of children received well-child care from a private physician; for more than half of this group, the parents cited cost as the reason for using the health department, even though their physician was participating in the state universal purchase program. Of the 8 parents who told their child's private physician that they could not afford immunizations, none was told that the vaccine administration fee would be waived. CONCLUSIONS: Even though North Carolina's universal vaccine purchase program had been in effect for more than 2 years, a substantial number of children still received care from a private physician but used the health department for immunizations because of cost. These results indicate a need to explore additional strategies to preserve children's "medical homes."

Adult↗
PubMed1998

Sequence-specific methylation of the mouse H19 gene in embryonic cells deficient in the Dnmt-1 gene.

We have used Dnmtc/c ES cells that are homozygous for disruption of the DNA methyltransferase gene to address how de novo methylation is propagated and whether it is directed to specific sites in the early embryo. We examined the imprinted H19 gene and the specific-sequence region implicated as an "imprinting mark" to determine whether de novo methylation was occurring at a restricted set of sites. Since the "imprinting mark" was found to be methylated differentially at all stages of development, we reasoned that the sequence may still be a target for the de novo methylation activity found in the Dnmtc/c cells, even though the loss of maintenance the methylase activity renders the H19 promoter active. We used bisulfite genomic sequencing to determine the methylation state of the imprinted region of the H19 gene and found a low level of DNA methylation at specific single CpG sites in the upstream region of the imprinted H19 sequence in the Dnmtc/c mutant ES cells. Moreover, these CpG sites appeared to be favoured targets for further de novo methylation of neighbouring CpG sites in rescued ES cells, which possess apparently normal maintenance activity. Our data provide further evidence for a separate methylating activity in ES cells and indicate that this activity displays sequence specificity.

Animals↗
PubMed1998

Implications of predator foraging on aphid pathogen dynamics.

The foraging behavior of starved and nonstarved second and fourth instar Coccinella septempunctata larvae on dead Acyrthosiphon pisum aphids, either infected with the entomopathogenic fungus Erynia neoaphidis (sporulating) or uninfected, was examined. Larvae searched for longer and fed less when presented with infected rather than uninfected A. pisum. Although no sporulating infected aphids were completely consumed, both adult and larval ladybirds can still be considered as intraguild predators. In a further study, fourth instar larvae fed on dying infected, dead infected (not sporulating), and dead uninfected aphids for similar periods of time but again the infected aphids were seldom entirely consumed. Live uninfected aphids were fed upon for significantly longer than any other prey. Infected aphids which were damaged at an early stage of infection (0, 1, or 2 days after inoculation) did not sporulate, whereas damaged moribund aphids (3 days after inoculation) did subsequently sporulate. Damaged sporulating cadavers continued to sporulate. However, damage to moribund and sporulating infected aphids, both mechanical or due to C. septempunctata feeding, reduced the number of conidia subsequently produced. Larval feeding caused the most significant reduction. Under laboratory conditions, C. septempunctata foraging on infected aphids did, therefore, reduce the pathogen density. However, conidia produced from a damaged cadaver resulted in levels of transmission to healthy aphids comparable to that resulting from an intact cadaver. Furthermore, the presence of a foraging adult ladybird resulted in a significant increase in transmission of the fungus to healthy aphids. Preliminary studies to assess the potential of other aphid natural enemies as intraguild predators illustrated that adults of the generalist carabid, Pterostichus madidus, entirely consumed sporulating cadavers. Third instar lacewing, Chrysoperla carnea, and hoverfly, Episyrphus balteatus, larvae never fed on sporulating cadavers. The ecological implications of these results are discussed.

Animals↗
PubMed1998

Adopting immunization recommendations: a new dissemination model.

OBJECTIVE: This paper presents a new approach for understanding factors related to physician adoption of clinical guidelines, using children's vaccine recommendations as a case study. METHODS: The model traces sequential steps, from awareness to agreement to adoption and, finally, adherence to the guideline. Movement through these stages can be catalyzed or retarded by many influences, grouped into two major categories: environmental characteristics of the physician's practice, and information characteristics of the guideline. Environmental characteristics include sociocultural factors, professional characteristics, and practice organization factors. Information characteristics include the guideline's relative advantage, complexity, and compatibility with existing guidelines and protocols, as well as mechanisms of guideline dissemination. IMPLICATIONS: This model can be used to identify characteristics that will likely impede or facilitate guideline adoption, and to focus dissemination efforts on key issues.

Child↗
PubMed1998

Increased DNA methyltransferase expression in leukaemia.

Aberrant DNA methylation has been observed consistently in many human tumours, in particular in the CpG islands of tumour suppressor genes, but the underlying mechanism of these changes remains unclear. To determine whether DNA methyltransferase expression is increased in leukaemia, we developed a standardised competitive RT-PCR assay to measure the level of DNA methyltransferase transcripts. Using this assay on bone marrow RNA samples from 12 patients with acute leukaemia, we observed a 4.4-fold mean increase in the level of DNA methyltransferase mRNA compared with normal bone marrow. These results support but do not prove the hypothesis that an increase in DNA methyltransferase activity is associated with malignant haematological diseases and may constitute a key step in carcinogenesis.

Adult↗
PubMed1997

Detection and measurement of PCR bias in quantitative methylation analysis of bisulphite-treated DNA.

Methylation analysis of individual cytosines in genomic DNA can be determined quantitatively by bisulphite treatment and PCR amplification of the target DNA sequence, followed by restriction enzyme digestion or sequencing. Methylated and unmethylated molecules, however, have different sequences after bisulphite conversion. For some sequences this can result in bias during the PCR amplification leading to an inaccurate estimate of methylation. PCR bias is sequence dependent and often strand-specific. This study presents a simple method for detection and measurement of PCR bias for any set of primers, and investigates parameters for overcoming PCR bias.

5-Methylcytosine↗
PubMed1997

Sp1 binding is inhibited by (m)Cp(m)CpG methylation.

Previously it has been found that binding of the Sp1 transcription factor is not significantly affected by methylation of the CpG dinucleotide within its binding site, 5'-GGGCGG (lower strand, 5'-CCGCCC). Since it has been established that mammalian cells also have the capacity to methylate cytosines (C) at CpNpG sites we examined the effect of methylation of the outer C of the CpCpG on Sp1 binding. We find that methylation of the outer C is inhibitory and in particular methylation of both cytosines (m)Cp(m)CpG inhibits binding by 95%. Furthermore, we have identified endogenous (m)Cp(m)CpG methylation of an Sp1 site in the CpG island promoter of the retinoblastoma (Rb) gene by genomic sequencing. This occurs in a proportion of retinoblastoma tumors which are extensively CpG methylated in the Rb promoter. The results raise the possibility that (m)Cp(m)CpG methylation could have a biological function in preventing Sp1 binding, thereby contributing to the subsequent abnormal methylation of CpG islands often observed in tumor cells.

Binding Sites↗