We have characterized the newly developed thyroid hormone antagonist NH-3 in both cell culture and in vivo model systems. NH-3 binds Xenopus laevis thyroid hormone receptors directly in vitro and induces a conformation distinct from agonist-bound receptors. Transcriptional activation of a thyroid hormone response element-containing reporter gene is strongly inhibited by NH-3 in a dose-dependent manner. In addition, NH-3 prevents X. laevis thyroid hormone receptors from binding to the p160 family of co-activators GRIP-1 and SRC-1 in a two-hybrid assay. To assess the potency of the compound in vivo, we used induced and spontaneous X. laevis tadpole metamorphosis, a thyroid hormone-dependent developmental process. NH-3 inhibits thyroid hormone-induced morphological changes in a dose-dependent manner and inhibits the up-regulation of endogenous thyroid hormone-responsive genes. Spontaneous metamorphosis is efficiently and reversibly arrested by NH-3 with at least the same effectiveness as the thyroid hormone synthesis inhibitor methimazole. Therefore, NH-3 is the first thyroid hormone antagonist to demonstrate potent inhibition of thyroid hormone action in both cell culture-and whole animal-based assays.

A major challenge in understanding nuclear hormone receptor function is to determine how the same ligand can cause very different tissue-specific responses. Tissue specificity may result from the presence of more than one receptor subtype arising from multiple receptor genes or alternative splicing. Recently, high affinity analogs of nuclear receptor ligands have been synthesized that show subtype selectivity. These analogs can greatly facilitate the study of receptor subtype-specific functions in organisms where mutational analysis is problematic or where it is desirable for receptors to be expressed in their normal physiological contexts. We describe here the effects of the synthetic thyroid hormone analog GC-1 on the metamorphosis of the frog Xenopus laevis. The most potent natural thyroid hormone, 3,5,3-triidothyronine or T3, shows similar binding affinity and transactivation dose-response curves for both thyroid hormone receptor isotypes, designated TR␣ and TR␤. GC-1, however, binds to and activates TR␤ at least an order of magnitude better than it does TR␣. GC-1 efficiently induces death and resorption of premetamorphic tadpole tissues such as the gills and the tail, two tissues that strongly induce thyroid hormone receptor ␤ during metamorphosis. GC-1 has less effect on the growth of adult tissues such as the hindlimbs, which express high TR␣ levels. The effectiveness of GC-1 in inducing tail resorption and tail gene expression correlates with increasing TR␤ levels. These results illustrate the utility of subtype selective ligands as probes of nuclear receptor function in vivo.

rST represents an important cause of long-term morbidity and mortality after an initial ST. Bifurcation ST and a larger proximal reference vessel diameter are independently associated with an increased risk of rST.

Developing Xenopus laevis experience two periods of muscle differentiation, once during embryogenesis and again at metamorphosis. During metamorphosis, thyroid hormone induces both muscle growth in the limbs and muscle death in the tail. In mammals, the muscle creatine kinase (MCK) gene is activated during the differentiation from myoblasts to myocytes and has served as both a marker for muscle development and to drive transgene expression in transgenic mice. Transcriptional control elements are generally highly conserved throughout evolution, potentially allowing mouse promoter use in transgenic X. laevis. This paper compares endogenous X. laevis MCK gene expression and the mouse MCK (mMCK) promoter driving a green fluorescent protein reporter in transgenic X. laevis. The mMCK promoter demonstrated strong skeletal muscle-specific transgene expression in both the juvenile tadpole and adult frog. Therefore, our results clearly demonstrate the functional conservation of regulatory sequences in vertebrate muscle gene promoters and illustrate the utility of using X. laevis transgenesis for detailed comparative study of mammalian promoter activity in vivo.

The cowpea (Vigna unguiculata) line Arlington, inoculated with Cowpea mosaic virus (CPMV), showed no symptoms, and no infectivity or accumulation of capsid antigen was detected at several days after inoculation. Coinoculation, but not sequential inoculation, of CPMV with similar concentrations of another Comovirus; Cowpea severe mosaic virus (CPSMV), resulted in reduced numbers of CPSMV-induced lesions. This apparent, CPMV-mediated reduction in number of CPSMV-induced infection centers was termed concurrent protection. We report results obtained by inoculating two nearly isogenic cowpea lines derived from a CPMV-susceptible cowpea crossed to Arlington, one line CPMV-susceptible and the other resistant. The CPMV virions B and M, encapsidating genomic RNAs 1 and 2, respectively, were extensively purified by gradient centrifugation. In the CPMV-resistant cowpea, either CPMV or CPMV B affected concurrent protection against CPSMV and against two distinct non-Comoviruses: Cherry leafroll virus and Southern bean mosaic virus. Adding CPMV M to the inoculum did not enhance CPMV-B-mediated protection. CPMV B was ineffective in protecting CPMV-susceptible cowpea. We postulate that CPMV-mediated concurrent protection is elicited in CPMV-resistant cowpea by a CPMV RNA-1-encoded factor and acts to reduce accumulation or spread of CPMV and certain coinoculated challenging viruses in or from the inoculated cell. Coinoculated CPMV did not protect CPMV-resistant cowpea against Tomato bushy stunt virus or Cucumber mosaic virus.