A truncated acidic domain in Xenopus TRF1.

Telomere function is mediated by a complex of proteins bound to double-stranded and single-stranded telomeric repeats. A key player in this complex is TRF1, which binds to duplex TTAGGG repeats and acts as a negative regulator of telomere length. This protein's domain structure, as defined by studies with mammalian orthologs, consists of an N-terminal acidic domain, a dimerization domain, and a C-terminal Myb DNA binding domain. TRF1 from Xenopus laevis was cloned and sequenced, and the encoded protein found to have a similar structure but with a very short acidic domain. This short acidic domain was confirmed in Xenopus tropicalis, a true diploid, by cloning of cDNA sequences by RACE and analysis of the genomic locus. The TRF1 transcript is expressed in developing and adult frogs. Compared to the mammalian orthologs, the Xenopus genes are the most distantly related vertebrate examples characterized to date. Since adult Xenopus ubiquitously express somatic telomerase activity, proteins that regulate telomerase access to the chromosome ends are important in regulating telomere length in normal somatic tissue. The structure of Xenopus TRF1 has implications for its regulation by tankyrase.

Shifting attention in visual space: tests of moving-spotlight models versus an activity-distribution model.

Participants were induced to concentrate preparatory attention at a central location, to identify a letter there, to identify a 2nd letter to the extreme left or right of a central horizontal range of 5 locations, and then to identify a 3rd letter at 1 of the central 5 locations. Analog and discrete versions of the moving-spotlight model predict that response times to the 3rd letter will be most rapid at the location of the 2nd letter, whereas an activity-distribution model predicts that the most rapid responses to the 3rd letter will be at the central location, where preparatory attention is strongest. The data from 3 experiments, taken together, are inconsistent with the moving-spotlight models and are consistent with the activity-distribution model.

Didelphic uterus and unilaterally imperforate double vagina as an unusual presentation of right lower-quadrant abdominal pain.

Imperforate hymen should be considered in girls of menarcheal age with a history of amenorrhea and vague abdominal discomfort, particularly if associated with symptoms of urinary obstruction or constipation. Patients may present with severe dysmenorrhea and localized pain mimicking appendicitis if hematocolpometra is due to unilaterally imperforate hymen with duplicate vagina and didelphic uterus. Although this condition is exceedingly rare, the case presented stresses the importance of a careful history and physical examination of an adolescent girl presenting with symptoms of abdominal pain associated with menstruation.

Nonspecific cytotoxic cells in fish (Ictalurus punctatus). V. Metabolic requirements of lysis.

The mechanisms of lysis of nonspecific cytotoxic cells (NCC) from the channel catfish (Ictalurus punctatus) were studied by determining the effects of various inhibitors of cellular metabolism on cytolysis of NC-37 human lymphoma target cells. Inhibition of NCC-mediated lysis by dinitrophenol (DNP) and sodium azide (NaN3) indicated a requirement for cellular energy metabolism. Cytochalasin B, an inhibitor of microfilaments, and monensin, an inhibitor of cellular secretion, both prevented lysis by NCC. Three microtubule inhibitors, vinblastine sulfate, colchicine, and demecolcine, all inhibited target cell lysis. Two divalent cation chelators, EDTA and EGTA, blocked NCC activity. Elimination of both Ca2+ and Mg2+ by EDTA prevented target cell binding and killing. Selective removal of Ca2+ by EGTA prevented killing but did not block target cell binding. These results indicated that nonspecific cytotoxicity in fish is an active process which requires cell movement and an intact secretory apparatus. The mechanisms of cytolysis by NCC were found (except for the requirement of microtubules) to be analogous to those of mammalian NK cells. Combined with morphological studies, these data strongly suggest that a phylogenetic relationship exists between these effector cells.

Nonspecific cytotoxic cells in fish (Ictalurus punctatus). III. Biophysical and biochemical properties affecting cytolysis.

Nonspecific cytotoxic cells (NCC) from the catfish (Ictalurus punctatus) may comprise a population of cells that are responsible for cellular immunity in the fish. NCC kill a wide variety of transformed target cells, and previous studies have indicated that NCC share properties with mammalian natural killer cells. In the present study, many biophysical and biochemical properties of NCC were defined. NCC were nylon wool nonadherent and adherent. NCC activity was also enriched in plastic nonadherent cells. NCC were nonphagocytic (for carbonyl iron), and they did not bind to Sephadex G-10. Characterization of NCC by density gradient centrifugation indicated that they comprise a relatively homogenous population of cytolytic cells that band at 45.5% Percoll. Moderate to high doses (500-2500 R) of X-irradiation produced a stimulatory effect on NCC lysis of labeled target cells. Additional studies indicated that a soluble suppressor protein in catfish serum (CFS) regulated NCC activity. This S. aureus protein A binding component isolated from CFS suppressed NCC activity. Analysis by SDS-PAGE indicated that the soluble regulatory protein had properties similar to immunoglobulin. These data indicate that NCC share some biophysical properties with mammalian natural killer cells. In addition, NCC appear to be under partial cell regulation by a radiation sensitive suppressor cell and also by a soluble regulator serum immunoglobulin component.

Nonspecific cytotoxic cells in fish (Ictalurus punctatus). IV. Target cell binding and recycling capacity.

The morphology of nonspecific cytotoxic cells (NCC) was identified. NCC were purified by target cell conjugate formation and density gradient separation. NCC are monocyte-like. They have reniform nuclei and a low nucleus/cytoplasm ratio. Cytoplasmic granules were not seen after giemsa staining. Scanning electron microscopy demonstrated moderate surface villi and target cell attachment occurred via long membraneous filament-like surface projections extending to the target cell membranes. Transmission electron microscopy of effector:target cell conjugates revealed membrane contact areas without fusion or fragmentation. The nucleus of the NCC had accentuated peripheral chromation and a prominent Golgi apparatus; the cytoplasm contained osmiophilic granules. Michaelis-Menten and Lineweaver-Burk transformation of target cell binding revealed a Vmax of 11-15,000 and a Km of 40,000. The percentage of NCC bound to target cells was 16-18%. Results of these studies were combined with the conjugate experiment to obtain an estimated percentage of active NCC (5-7%). A maximum recycling capacity of .16-.30 indicated that once attachment by NCC to the target cell occurred (and a lethal signal delivered by an effector cell), either the NCC did not recycle or a long lag period was required to restore its cytotoxic capability.

The pass/fail disparity among three commonly employed articulatory screening tests.

This study compared children's performances on three screening tests of articulation. The Templin-Darley Screening Test of Articulation, the Screening Deep Test of Articulation, and the Predictive Screening Test of Articulation were administered to 91 first graders ranging in age from 5:6 to 7:0 years of age. Comparisons were made in terms of the number of individuals failed. Results indicated that while there was no significant difference between the numbers of individuals failing each test, there was poor correlation between the tests in terms of the particular individuals failed. Of the 11 children failing one or more of the tests, only one failed all three. Results are discussed in terms of their clinical implications.