Delineation of the IGF-II C domain elements involved in binding and activation of the IR-A, IR-B and IGF-IR.

OBJECTIVE: Human insulin-like growth factor-I and -II (IGF-I and -II) ligands share a high degree of sequence and structural homology. Despite their similarities, IGF-I and IGF-II exhibit differential receptor binding and activation characteristics. The C domains of IGF-I and IGF-II are the primary determinants of binding specificity to the insulin-like growth factor I receptor (IGF-IR), insulin receptor exon 11- (IR-A) and exon 11+ (IR-B) isoforms. DESIGN: Three IGF-II analogues were generated in order to delineate the C domain residues that confer the differential receptor binding affinity and activation properties of the IGFs. Chimeric IGF-II analogues IGF-IICI(N) and IGF-IICI(C) contained partial IGF-I C domain substitutions (IGF-I residues underlined) GYGSSSRRSR and SRVSRRAPQT, respectively. RESULTS: The IGF-IICI(N) analogue bound the IR-A and IGF-IR with high affinity but bound the IR-B with a relatively lower affinity than IGF-II, suggesting a negative interaction between the exon-11 encoded peptide in the IR-B and the C-domain. The ability of IGF-IICI(N) to activate receptors and elicit cell viability responses was generally proportional to its relative receptor binding affinity but appeared to act as a partial agonist equivalent to IGF-I when binding and activating the IGF-IR. In contrast, IGF-IICI(C) bound IGF-IR with high affinity but elicited lower receptor activation and cell viability responses. Analogue IGF-IICI(S) contained a truncated IGF-I C domain (GSSSRRAT) and generally displayed a relatively poor ability to bind, activate and elicit viability responses via each receptor. CONCLUSIONS: Together, the IGF analogues demonstrate that both flanks of the IGF-II C domain play important roles in the greater ability of IGF-II to bind and activate IR receptors than IGF-I.

daf-16 integrates developmental and environmental inputs to mediate aging in the nematode Caenorhabditis elegans.

Evolutionary models of aging propose that a trade-off exists between the resources an organism devotes to reproduction and growth and those devoted to cellular maintenance and repair, such that an optimal life history always entails an imperfect ability to resist stress. Yet, since environmental stressors, such as caloric restriction or exposure to mild stress, can increase stress resistance and life span, it is possible that a common genetic mechanism could regulate the allocation of resources in response to a changing environment (for overview, see ). Consistent with predictions of evolutionary trade-off models, we show that nematodes carrying an integrated DAF-16::GFP transgene grow and reproduce more slowly yet are more stress resistant and longer lived than controls carrying the integration marker alone. We also show that the nuclear localization of the DAF-16::GFP fusion protein responds to environmental inputs as well as genetic. Environmental stresses, such as starvation, heat, and oxidative stress, cause rapid nuclear localization of DAF-16. In conditions rich in food, we find that DAF-16::GFP is inhibited from entry into the nucleus by daf-2 and akt-1/akt-2, both components of insulin-like signaling in nematodes. We suggest that changes in the subcellular localization of DAF-16 by environmental cues allows for rapid reallocation of resources in response to a changing environment at all stages of life.

Gestational diabetes.

OBJECTIVE: To review the detection, diagnosis, and clinical management of gestational diabetes. DATA SOURCES: MEDLINE, Gestational Diabetes Guideline Review, 1968-1998. STUDY SELECTION: By the author. DATA EXTRACTION: By the author. DATA SYNTHESIS: Gestational diabetes is a common complication of pregnancy, occurring in 2% to 6% of pregnancies. Uncontrolled gestational diabetes is associated with increased infant morbidity and mortality, macrosomia, and cesarean deliveries, and is a strong marker for the future development of maternal diabetes mellitus. Women with risk factors for gestational diabetes should be screened for glucose intolerance at 24 to 28 weeks' gestation. If a screening plasma glucose concentration is 140 mg/dL or greater one hour after a 50 gram oral glucose load, then a diagnostic 100 gram, three-hour oral glucose tolerance test should be performed. Medical nutrition therapy is the cornerstone of management and must be designed to meet individual needs. Self-monitoring of blood glucose should be taught to and performed by all women with gestational diabetes. Insulin, which does not readily cross the placental barrier, is the drug therapy of choice in women failing medical nutrition therapy. CONCLUSION: Pharmacists can optimize overall care by educating, monitoring, and intervening or assisting the patient in the management of gestational diabetes.

Functional domains of LAG-2, a putative signaling ligand for LIN-12 and GLP-1 receptors in Caenorhabditis elegans.

The LAG-2 membrane protein is a putative signaling ligand for the LIN-12 and GLP-1 receptors of Caenorhabditis elegans. LAG-2, like its Drosophila homologues Delta and Serrate, acts in a conserved signal transduction pathway to regulate cell fates during development. In this article, we investigate the functional domains of LAG-2. For the most part, mutants were constructed in vitro and assayed for activity in transgenic animals. We find a functional role for all major regions except one. Within the extracellular domain, the N-terminal region, which bears no known motif, and the DSL domain are both required. By contrast, the region bearing epidermal growth factor-like repeats can be deleted with no apparent reduction in rescuing activity. The intracellular region is not required for activity but instead plays a role in down-regulating LAG-2 function. Finally, membrane association is critical for mutant rescue.

lag-2 may encode a signaling ligand for the GLP-1 and LIN-12 receptors of C. elegans.

The C. elegans lag-2 gene is required for several cell-cell interactions that rely on the receptors GLP-1 and LIN-12. In this paper, we report that lag-2 encodes a putative membrane protein with sequence similarity to Drosophila Delta, a proposed ligand for the Notch receptor. Furthermore, we show that the lag-2 promoter drives expression of a reporter protein in the signaling distal tip cell (DTC) of the DTC/germline interaction. By in situ hybridization, we have found that endogenous lag-2 mRNA is present in the DTC but not the germ line. One fusion protein, called LAG-2::beta-gal(intra), rescues a lag-2 null mutant and can be detected in both DTC and germ line. Taking these results together, we propose that lag-2 may encode a signaling ligand for GLP-1/LIN-12 and that the entire LAG-2 protein may be taken up into the receiving cell during induction by GLP-1 and lateral signaling by LIN-12.

Instability of a plasmid-borne inverted repeat in Saccharomyces cerevisiae.

Inverted repeated DNA sequences are common in both prokaryotes and eukaryotes. We found that a plasmid-borne 94 base-pair inverted repeat (a perfect palindrome of 47 bp) containing a poly GT sequence is unstable in S. cerevisiae, with a minimal deletion frequency of about 10(-4)/mitotic division. Ten independent deletions had identical end points. Sequence analysis indicated that all deletions were the result of a DNA polymerase slippage event (or a recombination event) involving a 5-bp repeat (5' CGACG 3') that flanked the inverted repeat. The deletion rate and the types of deletions were unaffected by the rad52 mutation. Strains with the pms1 mutation had a 10-fold elevated frequency of instability of the inverted repeat. The types of sequence alterations observed in the pms1 background, however, were different than those seen in either the wild-type or rad52 genetic backgrounds.

Saccharomyces cerevisiae RAD5-encoded DNA repair protein contains DNA helicase and zinc-binding sequence motifs and affects the stability of simple repetitive sequences in the genome.

rad5 (rev2) mutants of Saccharomyces cerevisiae are sensitive to UV light and other DNA-damaging agents, and RAD5 is in the RAD6 epistasis group of DNA repair genes. To unambiguously define the function of RAD5, we have cloned the RAD5 gene, determined the effects of the rad5 deletion mutation on DNA repair, DNA damage-induced mutagenesis, and other cellular processes, and analyzed the sequence of RAD5-encoded protein. Our genetic studies indicate that RAD5 functions primarily with RAD18 in error-free postreplication repair. We also show that RAD5 affects the rate of instability of poly(GT) repeat sequences. Genomic poly(GT) sequences normally change length at a rate of about 10(-4); this rate is approximately 10-fold lower in the rad5 deletion mutant than in the corresponding isogenic wild-type strain. RAD5 encodes a protein of 1,169 amino acids of M(r) 134,000, and it contains several interesting sequence motifs. All seven conserved domains found associated with DNA helicases are present in RAD5. RAD5 also contains a cysteine-rich sequence motif that resembles the corresponding sequences found in 11 other proteins, including those encoded by the DNA repair gene RAD18 and the RAG1 gene required for immunoglobin gene arrangement. A leucine zipper motif preceded by a basic region is also present in RAD5. The cysteine-rich region may coordinate the binding of zinc; this region and the basic segment might constitute distinct DNA-binding domains in RAD5. Possible roles of RAD5 putative ATPase/DNA helicase activity in DNA repair and in the maintenance of wild-type rates of instability of simple repetitive sequences are discussed.

Instability of simple sequence DNA in Saccharomyces cerevisiae.

All eukaryotic genomes thus far examined contain simple sequence repeats. A particularly common simple sequence in many organisms (including humans) consists of tracts of alternating GT residues on one strand. Allelic poly(GT) tracts are often of different lengths in different individuals, indicating that they are likely to be unstable. We examined the instability of poly(GT) and poly(G) tracts in the yeast Saccharomyces cerevisiae. We found that these tracts were dramatically unstable, altering length at a minimal rate of 10(-4) events per division. Most of the changes involved one or two repeat unit additions or deletions, although one alteration involved an interaction with the yeast telomeres.

Fever of unknown origin in the elderly.

Fever is a prominent sign of an acute-phase response induced by microbial invasion, tissue injury, immunologic reactions, or inflammatory processes. This generalized host response is produced by a multiplicity of localized or systemic diseases and characterized by acute, subacute, or chronic changes in metabolic, endocrinologic, neurologic, and immunologic functions. The fundamental event is an initiation of the acute-phase response by the production of a mediated molecule called IL-1. This polypeptide is produced primarily from phagocytic cells such as blood monocytes, phagocytic lining cells of the liver and spleen, and other tissue macrophages. IL-1 produces a local reaction but also enters the circulation, acting as a hormone to mediate distant organ system responses to infection, immunologic reaction, and inflammatory processes. Fever is the result when IL-1 initiates the synthesis of prostaglandins, notably prostaglandin E2 in the thermoregulatory center located in the anterior hypothalamus. The thermostatic set point is then raised and mechanisms to conserve heat (vasoconstriction) and to produce heat (shivering) are initiated. The result is a sudden rise in body temperature. The same basic mechanisms are involved in FUO. Many of the biologic and biochemical changes that are seen in FUO are also evidence of an acute-phase response. The elevated erythrocyte sedimentation rate is partly due to increased synthesis of hepatic proteins, including compliment components, ceruloplasmin, fibrinogen, and C-reactive protein. IL-1 acts directly on the bone marrow to increase absolute numbers and immaturity of circulating neutrophils. Anemia is produced by many mechanisms, including the reduction of circulating serum iron. Although fever production in the elderly maybe delayed or of less intensity, it is still a marker of significant disease.(ABSTRACT TRUNCATED AT 400 WORDS)