PubMed Health⌕ Search

Biomedical subjects

Donald Evans

Publications and source records attributed to Donald Evans.

9 recordsLinked to original sources
PubMed2025

Differential methylation clock ages across buffy coat (BC), peripheral blood mononuclear cells (PBMC), and saliva in individuals approaching midlife.

Understanding epigenetic aging prior to midlife is gaining interest as a potentially intervenable period to address factors that influence health and cognitive aging. Epigenetic changes associated with aging may point to differential biological aging rates; however, methylation profiles may not be substitutable across tissues. We compared DNA methylation in three tissues collected in 91 siblings and twins from the Colorado Adoption/Twin Study of Lifespan behavioral development and cognitive aging (CATSLife1): saliva, buffy coat (BC), and peripheral blood mononuclear cells (PBMC). Overall, across five methylation clocks and two blood-derived and one saliva-derived tissues, moderate to strong associations between chronological age and methylation ages were observed. Moreover, PBMC methylation age values correlate more strongly with BC values (Spearman r = 0.66 - 0.87), whereas saliva showed weaker correlations with either form of blood-derived measures (Spearman r = 0.25 - 0.69) although still moderate to strong magnitudes. Saliva demonstrated significantly older methylation ages across four of five clocks, whereas PBMC and BC did not differ. Twins were more strongly correlated for BC and PBMC derived clocks with weaker and inconsistent patterns among Saliva clocks. DunedinPACE age acceleration showed no significant tissue differences and on average demonstrated the largest divergence of similarity between monozygotic (MZ) versus dizygotic (DZ) twins (rMZ= .56, rDZ= .21). In summary, saliva-derived methylation is not a direct substitute for blood-derived methylation whereas blood-derived methylation values were comparable across buffy coat and peripheral blood mononuclear cell tissues.

age acceleration↗
PubMed2006

Structure and function of eukaryotic Ribonuclease P RNA.

Ribonuclease P (RNase P) is the ribonucleoprotein endonuclease that processes the 5' ends of precursor tRNAs. Bacterial and eukaryal RNase P RNAs had the same primordial ancestor; however, they were molded differently by evolution. RNase P RNAs of eukaryotes, in contrast to bacterial RNAs, are not catalytically active in vitro without proteins. By comparing the bacterial and eukaryal RNAs, we can begin to understand the transitions made between the RNA and protein-dominated worlds. We report, based on crosslinking studies, that eukaryal RNAs, although catalytically inactive alone, fold into functional forms and specifically bind tRNA even in the absence of proteins. Based on the crosslinking results and crystal structures of bacterial RNAs, we develop a tertiary structure model of the eukaryal RNase P RNA. The eukaryal RNA contains a core structure similar to the bacterial RNA but lacks specific features that in bacterial RNAs contribute to catalysis and global stability of tertiary structure.

Azides↗
PubMed2006

RNase P: interface of the RNA and protein worlds.

Ribonuclease P (RNase P) is an endonuclease involved in processing tRNA. It contains both RNA and protein subunits and occurs in all three domains of life: namely, Archaea, Bacteria and Eukarya. The RNase P RNA subunits from bacteria and some archaea are catalytically active in vitro, whereas those from eukaryotes and most archaea require protein subunits for activity. RNase P has been characterized biochemically and genetically in several systems, and detailed structural information is emerging for both RNA and protein subunits from phylogenetically diverse organisms. In vitro reconstitution of activity is providing insight into the role of proteins in the RNase P holoenzyme. Together, these findings are beginning to impart an understanding of the coevolution of the RNA and protein worlds.

Animals↗
PubMed2002

A global analysis of Caenorhabditis elegans operons.

The nematode worm Caenorhabditis elegans and its relatives are unique among animals in having operons. Operons are regulated multigene transcription units, in which polycistronic pre-messenger RNA (pre-mRNA coding for multiple peptides) is processed to monocistronic mRNAs. This occurs by 3' end formation and trans-splicing using the specialized SL2 small nuclear ribonucleoprotein particle for downstream mRNAs. Previously, the correlation between downstream location in an operon and SL2 trans-splicing has been strong, but anecdotal. Although only 28 operons have been reported, the complete sequence of the C. elegans genome reveals numerous gene clusters. To determine how many of these clusters represent operons, we probed full-genome microarrays for SL2-containing mRNAs. We found significant enrichment for about 1,200 genes, including most of a group of several hundred genes represented by complementary DNAs that contain SL2 sequence. Analysis of their genomic arrangements indicates that >90% are downstream genes, falling in 790 distinct operons. Our evidence indicates that the genome contains at least 1,000 operons, 2 8 genes long, that contain about 15% of all C. elegans genes. Numerous examples of co-transcription of genes encoding functionally related proteins are evident. Inspection of the operon list should reveal previously unknown functional relationships.

Animals↗
PubMed1996

Covert video surveillance -- a response to Professor Southall and Dr. Samuels.

In their reply to my recent paper on Munchausen's syndrome by proxy, Professor Southall and Dr. Samuels concede that some things may be learned from my observations. They do not attend to the main argument of the paper, however, that the proportion of research interest in their use of covert video surveillance merits consideration of the research protocol by an independent research ethics committee. It will not do simply to assert that the use of this technology for the purposes outlined in their accounts is not research. I formulated arguments based on facts divulged in those published accounts for regarding their work as containing a considerable proportion of research activity. Unfortunately their reply did not address these arguments. Until such points are adequately answered the protection of patients calls for satisfactory judgments to be made on certain important issues which any research ethics committee would be obliged to consider in an evaluation of their activities. I suggest that some of these features will create more difficulties for approval of such a protocol than others.

Behavioral Research↗