Fos family members induce cell cycle entry by activating cyclin D1.

Expression of the fos family of transcription factors is stimulated by growth factors that induce quiescent cells to reenter the cell cycle, but the cellular targets of the Fos family that regulate cell cycle reentry have not been identified. To address this issue, mice that lack two members of the fos family, c-fos and fosB, were derived. The fosB-/- c-fos-/- mice are similar in phenotype to c-fos-/- mice but are 30% smaller. This decrease in size is consistent with an abnormality in cell proliferation. Fibroblasts derived from fosB-/- c-fos-/- mice were found to have a defect in proliferation that results at least in part from a failure to induce cyclin D1 following serum-stimulated cell cycle reentry. Although definitive evidence that c-Fos and FosB directly induce cyclin D1 transcription will require further analysis, these findings raise the possibility that c-Fos and FosB are either direct or indirect transcriptional regulators of the cyclin D1 gene and may function as a critical link between serum stimulation and cell cycle progression.

Competitive binding of alpha-actinin and calmodulin to the NMDA receptor.

The mechanisms by which neurotransmitter receptors are immobilized at postsynaptic sites in neurons are largely unknown. The activity of NMDA (N-methyl-D-aspartate) receptors is mechanosensitive and dependent on the integrity of actin, suggesting a functionally important interaction between NMDA receptors and the postsynaptic cytoskeleton. alpha-Actinin-2, a member of the spectrin/dystrophin family of actin-binding proteins, is identified here as a brain postsynaptic density protein that colocalizes in dendritic spines with NMDA receptors and the putative NMDA receptor-clustering molecule PSD-95. alpha-Actinin-2 binds by its central rod domain to the cytoplasmic tail of both NR1 and NR2B subunits of the NMDA receptor, and can be immunoprecipitated with NMDA receptors and PSD-95 from rat brain. Intriguingly, NR1-alpha-actinin binding is directly antagonized by Ca2+/calmodulin. Thus alpha-actinin may play a role in both the localization of NMDA receptors and their modulation by Ca2+.

Incidence of Fusarium spp. in Asparagus Spears.

Fusarium proliferatum and F. oxysporum have been identified as causal agents of asparagus decline in the field and have been associated with reduction in spear quality (1,2). Our objective was to determine the origin and incidence of spear infection by these fungi during the cropping years 1994 to 1997. From 15 to 40 asparagus samples were randomly selected from the field, packing houses, and retail markets and assayed for Fusarium spp. Collections were made in California, Connecticut, Peru, Mexico, and Australia. The number of samples varied between sampling sites and for the time of harvest season. One Mexican collection site was sampled at the beginning, mid-point, and end of the harvest season to evaluate influence of decreasing carbohydrate levels and increasing temperatures on infection and growth of the fungi. Isolations included sections (5 to 6 cm) from the basal and terminal portions of the spear to evaluate postharvest growth in the spear. Fusarium spp. were recovered from spear samples that included all geographical sampling locations (mean 45%, range 20 to 90%). F. proliferatum was the dominant species isolated consistently from the desert areas regardless of harvest period. The frequency of F. oxysporum isolation ranged from 2 to 32% with no correlation to time or location of sampling. Basal sections were more frequently infected (94%) than terminal portions of the spear (less than 6%). No major differences in the percentage of infected spears were found in collection sites regardless of country sampled. There were differences in the incidence of infection between harvest sample dates. Spears sampled late in the harvest period were 57% more infected than spears of early or mid-season collections. Samples from the same fields, regardless of whether collected directly from the field, from packing sheds, or from the retail market, had higher infection rates later in the harvest season compared with earlier harvests. This may be attributable to warmer temperatures, changes in levels of carbohydrates, or other physiological factors. Spears harvested from the field that were infected with both Fusarium spp. had a greater incidence of infection than spears recovered from packing houses or from retail sources. This supports the theory that the source of spear infection is diseased crowns and not postharvest sources. Isolates from the spears of both Fusarium spp. were found to be pathogenic when challenged to asparagus seedlings. References: (1) R. G. Grogan and K. A. Kimble. Phytopathology 49:122, 1959. (2) W. Schreuder et al. Plant Dis. 79:177, 1995.

Quality assurance of white blood cell labeling with a test based on adherence.

A new quality control assay was developed based on the premise that proper radioactive labeling should not affect the adherence characteristics of white blood cells to nylon fibers. Heparinized whole blood with trace amounts of radioactively labeled white blood cells was passed over nylon fiber columns and eluted in eight fractions. Percent radioactive adherence (%RA) and percent white blood cell adherence (%WBCA) were determined for each fraction. Regression lines (%RA versus %WBCA) were calculated for 9 samples labeled properly with 111In-oxine and for 17 samples intentionally subjected to improper labeling. Properly labeled preparations had a median slope = 1.05 and an intercept = 1%. Improperly labeled preparations had significantly lower slopes and/or higher intercepts. By the use of +/- 2 s.d. ranges as indicators of proper labeling (slope of 0.71-1.74; intercept of -35%-37%), the test had 100% sensitivity and 94% specificity. We conclude that proper labeling with 111In-oxine preserves the adherence characteristics of white blood cells, that improper labeling may affect the binding strength of white blood cells (decrease in slope) and/or lead to formation of sticky cell subgroups (increased intercept) and that the quality control assay can objectively assess the impact of labeling on adherence.

Resistance of Cotton to the Root-Knot Nematode, Meloidogyne incognita.

Cotton plants resistant to Meloidogyne incognita had roots characterized by fewer and smaller galls, and females that produced fewer egg masses containing fewer eggs than did susceptible plants. Many galls on resistant roots contained no nematodes at the time of examination. Penetration of the resistant cultivar was equal to that of the susceptible cultivar and independent of the number of nematodes in the inoculum. Fewer nematodes penetrated resistant or susceptible plants with eight leaves than those with fewer leaves. Reciprocal grafts of resistant and susceptible plants failed to confer resistance or susceptibility to the rootstock.

Post-Infection Development and Histopathology of Meloidogyne incognita in Resistant Cotton.

The numbers of Meloidogyne incognita larvae which migrated from cotton roots declined over a 16-day period, but the difference in numbers migrating from resistant and susceptible cultivars was not significant. Larvae penetrated susceptible roots, matured, and reproduced within 14 days following inoculation, whereas nematode development in the resistant roots was greatly retarded. Three types of histological responses were observed in infected, resistant roots, and these correlated with the degree of nematode development. Some galls were examined which contained only fragments of nematodes; others contained no detectable traces of developing larvae. Formation of druses in galls, but not in healthy tissue, was noted in both cultivars 20 days after inoculation. Massive invasion of roots resulted in deep longitudinal fissures of root cortex.