dazed gene is necessary for late cell type development and retinal cell maintenance in the zebrafish retina.

Several molecules, such as growth factors and neurotrophic factors, are required both for the differentiation of specific retinal cell types and the long-term cell survival of all retinal neurons. As diffusible factors, these molecules act non-cell-autonomously. Here, we describe the loss of function phenotype for dazed (dzd), a gene that acts cell-autonomously for retinal cell survival and affects the differentiation of rod photoreceptors and the Muller glia. By 3 days after fertilization, dazed mutant embryos have small eyes and slight heart edema. Acridine orange staining indicated a significant degree of retinal cell death occurring by 48 hr after fertilization, and histological analysis revealed that dying cells were found in the inner and outer nuclear layers and near the marginal zones. Although molecular and morphological differentiation of the inner retina and cone photoreceptors occurred, rod photoreceptors failed to differentiate beyond a small patch in the ventral retina and rod precursors failed to respond to exogenously added retinoic acid, which normally potentiated rod differentiation. Mosaic analysis indicated that the dazed gene acts cell-autonomously for rod production and cell survival, as dazed clones failed to produce rods outside the ventral patch and dazed cells were not maintained in wild-type hosts. Raising mutants under constant light resulted in severe retinal degeneration, whereas raising embryos under constant darkness did not provide any additional protection from cell death. Behavioral analysis showed that a subpopulation of adult fish that were heterozygous for the dazed mutation had elevated visual thresholds and were night blind, suggesting that dazed may also be required for long-term dim-light vision. Taken together, our studies suggest a role for the dazed gene in rod and Muller cell development and overall retinal cell survival and maintenance.     

Evaluation of screened blood donations for human immunodeficiency virus type 1 infection by culture and DNA amplification of pooled cells

BACKGROUND. Reports of transmission of the human immunodeficiency virus type 1 (HIV-1) from transfusions of screened blood and reports of silent, antibody-negative HIV-1 infections in persons at high risk continue to foster concern about the safety of the blood supply. Previous estimates of the risk of HIV-1 range from 1 in 38,000 to 1 in 300,000 per unit of blood but are based on either epidemiologic models or the demonstration of seroconversion in recipients. METHODS. We isolated peripheral-blood mononuclear cells from blood that was fully screened and found to be seronegative, combined them into pools of cells from 50 donors, and tested them for HIV-1 by viral culture and the polymerase chain reaction, using protocols specifically adapted for this analysis. RESULTS. The 1530 pools of mononuclear cells were prepared from 76,500 blood donations made in San Francisco between November 1987 and December 1989. Of these pools, 1436 (representing 71,800 donations) were cultured successfully; 873 (43,650 donations) were evaluated by the polymerase chain reaction. Only one pool was confirmed as HIV-1--infected by both methods. After adjustment for sample-based estimates of the sensitivity of the detection systems using culture and the polymerase chain reaction, the probability that a screened donor will be positive for HIV-1 was estimated as 1 in 61,171 (95 percent upper confidence bound, 1 in 10,695). CONCLUSIONS. Silent HIV-1 infections are exceedingly rare among screened blood donors, so the current risk of HIV-1 transmission from blood transfusions, even in high-prevalence metropolitan areas, is extremely low.     

Transfer of a dense granule protein of Plasmodium falciparum to the membrane of ring stages and isolation of dense granules.

A 14-kDa protein was localized to the dense granules of Plasmodium falciparum by immunoelectron microscopy with monoclonal antibody 1H1. The protein was present in dense granules in late-stage schizonts and free merozoites. After invasion, the protein was localized exclusively on the membrane of the newly invaded ring. The protein is referred to as RIMA, for ring membrane antigen. The 14-kDa protein was synthesized late in schizogony as determined by immunofluorescence microscopy and immunoblotting. At the late schizont stage it was distributed diffusely throughout the intracellular schizont. Only at the segmenter stage was the protein localized in defined spots that correspond to dense granules. Dense granules were isolated from schizont-infected erythrocytes by subcellular fractionation on a sucrose gradient. Fractions containing the 14-kDa protein were detected by immunoblotting with monoclonal antibody 1H1. The 14-kDa protein was first detected in vesicles at the late (8-nucleus) schizont stage. Mature dense granules sedimented with a peak density of 1.17 g/ml, which is similar to the density of rhoptries isolated by the same procedure.     

Tobacco withdrawal in women and menstrual cycle phase

Because negative mood is a characteristic of both tobacco withdrawal and menstrual discomfort, withdrawal may vary by menstrual cycle phase. Tobacco withdrawal, mood, and menstrual discomfort were assessed in premenopausal women who quit smoking during either the follicular (Days 1-14 postmenstrual onset; n = 41) or luteal (Day 15 or longer postmenstrual onset; n = 37) phase of the menstrual cycle and maintained biochemically verified smoking abstinence during the postquit week. Women quitting during the luteal phase reported significantly greater increases in tobacco withdrawal and self-reported depressive symptoms than women quitting during the follicular phase. These results indicate that selecting a quit-smoking day early in the follicular phase may attenuate withdrawal and negative affect in premenopausal female smokers.     

Comparison of lymphocyte populations bearing surface immunoglobulins in avian bone marrow, bursa, spleen and thymus.

Rabbit anti-chicken gamma-globulin was labeled with 125I and then incubated with cells from the bursa, thymus, spleen, and bone marrow of 4- and 8-week old birds. The same procedure was carried out on 11-week-old agammaglobulinemic chickens. Autoradiography revealed that the majority of large, medium, and small bursal lymphocytes bind the antibodies while labeled lymphocytes of each type in the spleen and thymus never exceeded 11 or 4 percent, respectively. Labeled medium and small lymphocytes in the bone marrow increased from 4.2 and 1.7%, respectively, at 4 weeks of age, to 9.5 and 8.8%, respectively, at 8 weeks of age. Labeled lymphocytes of all sizes were completely absent in all tissues of agammaglobulinemic chicks, including the marrow. Therefore, the increase in frequency of labeled lymphocytes in the bone marrow with age may be a result of recruitment of cells from the bursa of Fabricius. The majority of lymphocytes in the bone marrow do not label. Therefore, lymphocytes from the bone marrow may be T cells, subsets of B cells, or neither T or B cells.