Structure and variability of human chromosome ends

Mammalian telomeres are thought to be composed of a tandem array of TTAGGG repeats. To further define the type and arrangement of sequences at the ends of human chromosomes, we developed a direct cloning strategy for telomere-associated DNA. The method involves a telomere enrichment procedure based on the relative lack of restriction endonuclease cutting sites near the ends of human chromosomes. Nineteen (TTAGGG)n-bearing plasmids were isolated, two of which contain additional human sequences proximal to the telomeric repeats. These telomere-flanking sequences detect BAL 31-sensitive loci and thus are located close to chromosome ends. One of the flanking regions is part of a subtelomeric repeat that is present at 10 to 25% of the chromosome ends in the human genome. This sequence is not conserved in rodent DNA and therefore should be a helpful tool for physical characterization of human chromosomes in human-rodent hybrid cell lines; some of the chromosomes that may be analyzed in this manner have been identified, i.e., 7, 16, 17, and 21. The minimal size of the subtelomeric repeat is 4 kilobases (kb); it shows a high frequency of restriction fragment length polymorphisms and undergoes extensive de novo methylation in somatic cells. Distal to the subtelomeric repeat, the chromosomes terminate in a long region (up to 14 kb) that may be entirely composed of TTAGGG repeats. This terminal segment is unusually variable. Although sperm telomeres are 10 to 14 kb long, telomeres in somatic cells are several kilobase pairs shorter and very heterogeneous in length. Additional telomere reduction occurs in primary tumors, indicating that somatic telomeres are unstable and may continuously lose sequences from their termini.

Syk is activated by phosphotyrosine-containing peptides representing the tyrosine-based activation motifs of the high affinity receptor for IgE

Engagement of the high affinity receptor for immunoglobulin E (Fc epsilon RI) on the surface of mast cells induces tyrosine phosphorylation of numerous cellular proteins. Syk, one of several non-receptor protein tyrosine kinases implicated in Fc epsilon RI signaling, is activated following receptor cross-linking and associates with phosphorylated gamma subunits of Fc epsilon RI. We previously showed that the Src homology 2 (SH2) domains of Syk bind with high affinity to the conserved tyrosine-based activation motif (TAM) of the gamma subunit in vitro. In this report, we show that a tyrosine-phosphorylated gamma TAM peptide induced tyrosine phosphorylation of Syk in RBL-2H3 cell lysates and stimulated Syk kinase activity 10-fold in vitro, with half-maximal activation at 1-2 microM. A similar beta subunit TAM peptide showed much lower stimulation of Syk tyrosine phosphorylation and kinase activity. Phosphopeptide-induced activation was inhibited by an antiserum to the carboxyl-terminal tail of Syk, suggesting that those amino acids are also involved in Syk activation. These results indicate that the catalytic domain of Syk may be regulated by intramolecular interactions with adjacent domains and suggest that Syk binding to phosphorylated gamma subunits following Fc epsilon RI engagement in vivo stimulates Syk kinase activity.

Interaction of p72syk with the gamma and beta subunits of the high-affinity receptor for immunoglobulin E, Fc epsilon RI

Activation of protein tyrosine kinases is one of the initial events following aggregation of the high-affinity receptor for immunoglobulin E (Fc epsilon RI) on RBL-2H3 cells, a model mast cell line. The protein tyrosine kinase p72syk (Syk), which contains two Src homology 2 (SH2) domains, is activated and associates with phosphorylated Fc epsilon RI subunits after receptor aggregation. In this report, we used Syk SH2 domains, expressed in tandem or individually, as fusion proteins to identify Syk-binding proteins in RBL-2H3 lysates. We show that the tandem Syk SH2 domains selectively associate with tyrosine-phosphorylated forms of the gamma and beta subunits of Fc epsilon RI. The isolated carboxy-proximal SH2 domain exhibited a significantly higher affinity for the Fc epsilon RI subunits than did the amino-proximal domain. When in tandem, the Syk SH2 domains showed enhanced binding to phosphorylated gamma and beta subunits. The conserved tyrosine-based activation motifs contained in the cytoplasmic domains of the gamma and beta subunits, characterized by two YXXL/I sequences in tandem, represent potential high-affinity binding sites for the dual SH2 domains of Syk. Peptide competition studies indicated that Syk exhibits a higher affinity for the phosphorylated tyrosine activation motif of the gamma subunit than for that of the beta subunit. In addition, we show that Syk is the major protein in RBL-2H3 cells that is affinity isolated with phosphorylated peptides corresponding to the phosphorylated gamma subunit motif. These data suggest that Syk associates with the gamma subunit of the high-affinity receptor for immunoglobulin E through an interaction between the tandem SH2 domains of SH2 domains of Syk and the phosphorylated tyrosine activation motif of the gamma subunit and that Syk may be the major signaling protein that binds to Fc epsilon RI tyrosine activation motif of the gamma subunit and that Syk may be the major signaling protein that binds to Dc epsilon tyrosine activation motifs in RBL-2H3 cells.

Lifestyle Medicine: A Brief Review of Its Dramatic Impact on Health and Survival

By ignoring the root causes of disease and neglecting to prioritize lifestyle measures for prevention, the medical community is placing people at harm. Advanced nations, influenced by a Western lifestyle, are in the midst of a health crisis, resulting largely from poor lifestyle choices. Epidemiologic, ecologic, and interventional studies have repeatedly indicated that most chronic illnesses, including cardiovascular disease, cancer, and type 2 diabetes, are the result of lifestyles fueled by poor nutrition and physical inactivity.In this article, we describe the practice of lifestyle medicine and its powerful effect on these modern instigators of premature disability and death. We address the economic benefits of prevention-based lifestyle medicine and its effect on our health care system: A system on the verge of bankruptcy. We recommend vital changes to a disastrous course. Many deaths and many causes of pain, suffering, and disability could be circumvented if the medical community could effectively implement and share the power of healthy lifestyle choices. We believe that lifestyle medicine should become the primary approach to the management of chronic conditions and, more importantly, their prevention. For future generations, for our own health, and for the Hippocratic Oath we swore to uphold ("First do no harm"), the medical community must take action. It is our hope that the information presented will inspire our colleagues to pursue lifestyle medicine research and incorporate such practices into their daily care of patients. The time to make this change is now.

A mammalian factor that binds telomeric TTAGGG repeats in vitro

We have identified a DNA-binding activity with specificity for the TTAGGG repeat arrays found at mammalian telomeres. This factor, called TTAGGG repeat factor (TRF), is present in nuclear extracts of human, mouse, and monkey cells. TRF from HeLa cells was characterized in detail by electrophoretic mobility shift assays. It binds double-stranded TTAGGG repeats in linear and circular DNAs. Single-stranded repeats are not recognized. The optimal site for TRF appears to contain more than six contiguous TTAGGG repeats. Tandem arrays of TAGGG, TTTAGGG, TTTTAGGG, TTGGGG, and TTAGGC repeats do not bind TRF well, indicating that TRF preferentially recognizes the telomeric repeat sequence present at mammalian chromosome ends. The apparent molecular mass of this factor, based on recovery of TRF from sodium dodecyl sulfate-polyacrylamide gels, is approximately 50 kDa. We suggest that TRF binds along the length of mammalian telomeres.

Evidence for an improvement in cognitive function following treatment of Schistosoma japonicum infection in Chinese primary schoolchildren

A double-blind, placebo-controlled, treatment trial was conducted in Sichuan, China to investigate the unique and combined effects on the cognitive function (working memory) of children after treating geohelminth infections with albendazole and treating Schistosoma japonicum infection with praziquantel. One hundred eighty-one children 5-16 years of age participated. At baseline, the praziquantel and placebo groups were similar in all background characteristics. Three months after praziquantel treatment, there was a significant reduction in the prevalence and intensity of S. japonicum infection. There were significant age group by praziquantel treatment interaction effects in three of the five cognitive tests, Fluency, Picture Search, and Free Recall, with effects being strongest in the youngest children (5-7 years old). Exploratory analysis within the youngest children showed a significant positive main effect of treatment on Fluency (P < 0.001), after controlling for sex, anthropometric, and parasitic and iron status. There was also a treatment by height-for-age interaction (P = 0.03) and a treatment by iron status interaction (P = 0.024) on Fluency. There was a treatment by S. japonicum intensity interaction (P < 0.001) on Free Recall, but the main effect of treatment on Picture Search was not significant (P = 0.058). Younger children and those who are physically the most vulnerable are likely to benefit the most from the treatment of S. japonicum infection in terms of improved performance on tests of working memory.

A second chain of human CD8 is expressed on peripheral blood lymphocytes

Human CD8 has been thought to consist of disulfide-linked homodimers and homomultimers of a single polypeptide chain homologous to mouse and rat CD8 alpha. In contrast, mouse and rat CD8 are composed of disulfide-linked heterodimers of alpha and beta chains. We have now isolated and sequenced cDNA clones encoding a human homologue of mouse and rat CD8 beta. One such clone was inserted into an expression vector and its encoded product was shown to be expressed on the cell surface after cotransfection into L cells with the human CD8 alpha gene. A second form of human CD8 beta cDNA encoding a protein with an altered cytoplasmic tail was similarly transfected, but its product could not be demonstrated on the cell surface. CD8 beta was further shown to be expressed on the surface of almost all CD8+ human peripheral blood T cells. These data provide the first evidence that human CD8 is a heterodimeric protein.

Site-directed mutagenesis of HIV-1 integrase demonstrates differential effects on integrase functions in vitro

The retroviral integrase (IN) protein is essential for integration of retroviral DNA into the host cell genome. To identify functional domains within the protein and to assess the importance of conserved residues, we performed site-directed mutagenesis of HIV-1 IN and analyzed the mutants in vitro for IN-mediated activities: 3' processing (att site-specific nuclease activity), strand transfer (the joining of att site oligonucleotides to target DNA), disintegration (the reverse of strand transfer), and integration site selection. Changing the conserved residue His-16 either to Cys or to Val in a proposed zinc-finger region had minimal effect on IN activities. Alteration of two highly conserved amino acid residues, Asp-116-->Ile and Glu-152-->Gly, each resulted in complete or nearly complete loss of 3' processing, strand transfer, and disintegration, whereas alteration of another conserved residue, Trp-235-->Glu, had no demonstrable effect on any of the activities in vitro. Two mutants, Asp-64-->Val and Arg-199-->Cys delta, each demonstrated differential effects on IN activities. Asp-64-->Val has no demonstrable strand transfer or disintegration activity yet maintains 3' processing activity at a diminished level. Arg-199-->Cys delta, which lacks part of the carboxyl terminus of IN, has impaired strand transfer activity without loss of disintegration activity. Use of a target site selection assay showed that all of our mutants with strand transfer activity maintain the same integration pattern as wild type IN. We conclude that not all highly conserved IN residues are essential for IN activities in vitro, zinc coordination by the proposed zinc-finger domain may not be required for the activities assayed, alteration of single residues can yield differential effects on IN activities, and target site selection into naked DNA is not necessarily altered by changes in strand transfer activity.

Proposed Nutrition Competencies for Medical Students and Physician Trainees: A Consensus Statement

Importance

In 2022, the US House of Representatives passed a bipartisan resolution (House of Representatives Resolution 1118 at the 117th Congress [2021-2022]) calling for meaningful nutrition education for medical trainees. This was prompted by increasing health care spending attributed to the growing prevalence of nutrition-related diseases and the substantial federal funding via Medicare that supports graduate medical education. In March 2023, medical education professional organizations agreed to identify nutrition competencies for medical education.

Objective

To recommend nutrition competencies for inclusion in medical education to improve patient and population health.

Evidence Review

The research team conducted a rapid literature review to identify existing nutrition-related competencies published between July 2013 and July 2023. Additional competencies were identified from learning objectives in selected nutrition, culinary medicine, and teaching kitchen curricula; dietetic core competencies; and research team-generated de novo competencies. An expert panel of 22 nutrition subject matter experts and 15 residency program directors participated in a modified Delphi process and completed 4 rounds of voting to reach consensus on recommended nutrition competencies, the level of medical education at which they should be included, and recommendations for monitoring implementation and evaluation of these competencies.

Findings

A total of 15 articles met inclusion criteria for competency extraction and yielded 187 competencies. Through review of gray literature and other sources, researchers identified 167 additional competencies for a total of 354 competencies. These competencies were compiled and refined prior to voting. After 4 rounds of voting, 36 competencies were identified for recommendation: 30 at both undergraduate and graduate levels, 2 at the undergraduate level only, and 4 at the graduate level only. Competencies fell into the following nutrition-related themes: foundational nutrition knowledge, assessment and diagnosis, communication skills, public health, collaborative support and treatment for specific conditions, and indications for referral. A total of 36 panelists (97%) recommended nutrition competencies be assessed as part of licensing and board certification examinations.

Conclusions and Relevance

These competencies represent a US-based effort to use a modified Delphi process to establish consensus on nutrition competencies for medical students and physician trainees. These competencies will require an iterative process of institutional prioritization, refinement, and inclusion in current and future educational curricula as well as licensure and certification examinations.

Two wnt genes in Caenorhabditis elegans

wnt genes encode secretory glycoproteins that have been implicated in growth control and development in mice, frogs and insects. In this report we examine properties of two wnt genes recently identified in the nematode Caenorhabditis elegans. The first gene, Ce-wnt-1, was previously identified by a polymerase chain reaction-based screen of genomic DNA, and the second, Ce-wnt-2, was fortuitously encountered in a survey of clones in a cDNA library by the Caenorhabditis Genome Project. Full-length or nearly full-length cDNAs representing both mRNAs encode proteins that are similar in length, sequence and functional domains to other Wnt proteins. Primary products of 372 and 362 amino acids begin with a hydrophobic signal peptide, include two potential N-linked glycosylation sites and contain the 22 cysteine residues conserved throughout the wnt family. In contrast to mammalian and insect wnt genes with four or five exons and conserved intron-exon boundaries, Ce-wnt-1 has nine coding exons; only one of the eight identified introns interrupts the coding sequence at a position homologous to an intron position in other wnt genes. The major transcript derived from Ce-wnt-1 is 1.4 kb in length, and the 22 nucleotides at its 5' end are added by a trans-splicing mechanism. Ce-wnt-2 is also expressed via a single major transcript, 1.5 kb in length. Both RNAs are detectable in all larval forms and adults, but they are most abundant at the embryonic stage. Ce-wnt-1 is localized to the left arm of chromosome II and Ce-wnt-2 maps to a cluster of genes on chromosome IV.