Maternal serum screening in the Sioux Lookout Zone. Complicated test for an unspecified need

We investigated whether the incidence of fetal abnormalities among patients in Sioux Lookout Zone differs from incidence elsewhere in Canada, whether First Nations people would agree to screening, how information could be disseminated, and what practical considerations would affect implementation. Incidence appears to be similar to elsewhere, but First Nations people's cultural and spiritual beliefs and the difficulty of taking action once results are confirmed make current screening programs inappropriate.

B-cell signalling via the C-type lectins CD23 and CD72

Although CD23 and CD72 are well-known B-cell signalling molecules, the intracellular signal transduction pathways through which they operate remain poorly elucidated. This may partly reflect their somewhat dubious histories, with claims and counterclaims being made for functions and ligands. Here, John Gordon discusses why such controversy should surround the two B-cell-associated C-type lectins and provides speculation as to their respective roles in regulating an immune response that may be different in mice and humans.

Describing color appearance: hue and saturation scaling

Most of the fully elaborated systems for describing color appearance rely on matching to samples from some standard set. Since this is not satisfactory in all situations, various forms of direct linguistic description have been used, ranging from color naming to continuous numerical scaling of sensations. We have developed and extensively applied a particular variant in which subjects use percentage scales to describe their sensations of the four unique hue sensations (red, yellow, green, blue) and of the apparent saturation of colored lights. In this paper we explore the properties of this procedure, including its statistical properties and reliability both between and within subjects, in different contexts. We conclude that the technique is robust, easy to use, and provides direct access to sensory experience.

Antibodies to murine CD40 protect normal and malignant B cells from induced growth arrest

We have previously described the production of polyclonal anti-murine CD40 antibodies that specifically bind recombinant murine CD40 expressed on L cells and induce vigorous proliferation of normal murine B lymphocytes. The current study utilizes these antibodies to explore the distribution and function of CD40 in murine B cell development. Murine CD40 is expressed at high levels by normal splenic B cells and all Ig-positive B cell lymphomas tested to date. It is not expressed by the 70Z/3 pre-B cell line, BaF3 pre-B cell line, or by numerous T cell and myeloid cell lines. 70Z/3 pre-B cells can be induced to express CD40 by LPS stimulation of the cells. Stimulation of purified splenic B cells with anti-CD40 antibodies causes upregulation of class II MHC antigens, CD23, and ICAM-1 and results in extensive aggregation of the cells. Antibodies to murine CD40 are extremely effective at rescuing malignant and normal B cells from induced growth arrest. Anti-CD40 antibodies protect WEHI-231 and CH31 B lymphoma cells from growth arrest induced by soluble anti-IgM antibodies, TGF beta, or a combination of both stimulants. Similarly, anti-IgM preactivated normal splenic B cells which normally die rapidly from growth arrest after 1 or 2 days culture produce a vigorous proliferative response to subsequent stimulation with anti-CD40 antibodies plus IL-4. Interestingly, anti-CD40 antibodies provide little to no protection against B lymphoma growth arrest induced by immobilized anti-IgM antibodies. These data confirm and extend functional properties assigned previously to human CD40 and identify numerous defined murine model systems to explore the molecular basis of CD40-mediated protection from induced B cell growth arrest.

Physiologically inactive nucleoli contain nucleoplasmic ribonucleoproteins: immunoelectron microscopy of mouse spermatids and early embryos

Physiologically inactivating or reactivating nucleoli represent a good model to investigate modifications of the nucleolar activity, which influence to a great extent the morphology of this organelle. We have studied the nucleoli of mouse spermatids during gradual inactivation, as well as those of early mouse preimplantation embryos, which undergo reactivation. In the 2-cell systems, inactive nucleoli are represented by homogeneously, finely fibrillar spherical bodies. With the aim of clarifying the composition of these nucleoli, we have analyzed them by means of immunoelectron microscopy using specific antibodies directed against nucleoplasmic snRNPs, hnRNPs, ribosomal proteins, or fibrillarin as well as by cytochemical methods for visualizing DNA and RNA. Our results indicate that RNA is present in zygote and 2-cell nucleolus precursor bodies (NPBs) as well as in 4- to 8-cell or more advanced embryo nucleoli, but not in inactive spermatid nucleoli. DNA is absent from inactive spermatid nucleoli and NPBs but is present within the nucleolus-associated chromatin and the nucleolonema of active nucleoli. The dense masses constituting the NPBs of the zygote and 2-cell embryos contain ribosomal proteins and fibrillarin but also hnRNPs and nucleoplasmic snRNPs. Of these, only fibrillarin is present in the spermatid residual nucleoli.

Temporal tuning and the development of lateral interactions in the human visual system

PURPOSE

The authors examined the development of lateral interactions between neurons in the human visual system through the use of visual evoked potentials (VEPs) elicited by windmill-dartboard stimuli. Previously, these VEPs have revealed two distinct types of lateral interactions (short-range and long-range) in adults. This study aims to track the development of these interactions in the first 6 months of life.

METHOD

Windmill-dartboard stimuli were generated by a computer-controlled visual stimulator and presented on an oscilloscope display. VEPs to these stimuli were obtained from a group of human infants between 14 days and 6 months of age and from a group of adults who served as a basis for comparison. Fourier analysis was used to retrieve amplitude and phase measures of the relevant frequency components of the response.

RESULTS

Amplitude measures of the VEP components elicited by the windmill-dartboard stimulus showed that the attenuation of the second harmonic frequency component (reflecting long-range lateral interactions) was essentially adultlike at all temporal frequencies for the majority of infants. In contrast, the amplitude of the fundamental frequency component (thought to reflect short-range lateral interactions) exhibited a low-pass temporal tuning function in infants that differed dramatically from adults. Additional immaturities were observable in the phase of the fundamental component of the infant VEPs.

CONCLUSIONS

Evidence for the presence of some degree of lateral interaction was seen in even the youngest infant. Long-range lateral interactions appear to mature rapidly in infancy, whereas short-range lateral interactions show a much longer developmental time-course, and their properties are dependent on temporal frequency.

Stimulation of human B lymphocytes by phorbol esters reported to be selective in the protein kinase C isoforms they activate

It is reported here that B cells can be stimulated by two phorbol esters which, in cell free substrate phosphorylation assays, are selective in the PKC isoforms they activate: thymeleatoxin (Thy) stimulates all of the classical (c) or Group A PKCs (alpha, beta 1, beta 2 and gamma) but not PKC delta and epsilon which belong to the novel (n) or Group B PKCs, while 12-deoxyphorbol-13-O-phenylacetate-20-acetate (dPPA) is a specific activator of PKC beta 1. By itself, phorbol 12-myristate, 13-acetate (PMA)--which activates all cPKC and nPKC--was, on a molar basis, some 40-times more potent than either Thy or dPPA which were themselves equipotent at promoting DNA synthesis in resting B cells: the peak response achieved with Thy and dPPA was higher (1.4 x) than that obtained with PMA. In the presence of calcium ionophore, PMA, Thy and dPPA all stimulated a higher (and equivalent) peak response which was achieved at a lower phorbol ester concentration in each case: however, whereas Thy now approached PMA in potency, dPPA remained some 40-times less potent.

Accuracy of planar reaching movements. II. Systematic extent errors resulting from inertial anisotropy

This study examines the source of direction-dependent errors in movement extent made by human subjects in a reaching task. As in the preceding study, subjects were to move a cursor on a digitizing tablet to targets displayed on a computer monitor. Movements were made without concurrent visual feedback of cursor position, but movement paths were displayed on the monitor after the completion of each movement. We first examined horizontal hand movements made at waist level with the upper arm in a vertical orientation. Targets were located at five distances and two directions (30 degrees and 150 degrees) from one of two initial positions. Trajectory shapes were stereotyped, and movements to more distant targets had larger accelerations and velocities. Comparison of movements in the two directions showed that in the 30 degrees direction responses were hypermetric, accelerations and velocities were larger, and movement times were shorter. Since movements in the 30 degrees direction required less motion of the upper arm than movements in the 150 degrees direction, we hypothesized that the differences in accuracy and acceleration reflected a failure to take into account the difference in total limb inertia in the two directions. To test this hypothesis we simulated the initial accelerations of a two-segment limb moving in the horizontal plane with the hand at shoulder level when a constant force was applied at the hand in each of 24 directions. We compared these simulated accelerations to ones produced by our subjects with their arms in the same position when they aimed movements to targets in the 24 directions and at equal distances from an initial position. The magnitudes of both simulated and actual accelerations were greatest in the two directions perpendicular to the forearm, where inertial resistance is least, and lowest for movements directed along the axis of the forearm. In all subjects, the directional variation in peak acceleration was similar to that predicted by the model and shifted in the same way when the initial position of the hand was displaced. The pattern of direction-dependent variations in initial acceleration did not depend on the speed of movement. It was also unchanged when subjects aimed their movements toward targets presented within the workspace on the tablet instead of on the computer monitor. These findings indicate that, in programming the magnitude of the initial force that will accelerate the hand, subjects do not fully compensate for direction dependent differences in inertial resistance.(ABSTRACT TRUNCATED AT 400 WORDS)

Accuracy of planar reaching movements. I. Independence of direction and extent variability

This study examined the variability in movement end points in a task in which human subjects reached to targets in different locations on a horizontal surface. The primary purpose was to determine whether patterns in the variable errors would reveal the nature and origin of the coordinate system in which the movements were planned. Six subjects moved a hand-held cursor on a digitizing tablet. Target and cursor positions were displayed on a computer screen, and vision of the hand and arm was blocked. The screen cursor was blanked during movement to prevent visual corrections. The paths of the movements were straight and thus directions were largely specified at the onset of movement. The velocity profiles were bell-shaped, and peak velocities and accelerations were scaled to target distance, implying that movement extent was also programmed in advance of the movement. The spatial distributions of movement end points were elliptical in shape. The major axes of these ellipses were systematically oriented in the direction of hand movement with respect to its initial position. This was true for both fast and slow movements, as well as for pointing movements involving rotations of the wrist joint. Using principal components analysis to compute the axes of these ellipses, we found that the eccentricity of the elliptical dispersions was uniformly greater for small than for large movements: variability along the axis of movement, representing extent variability, increased markedly but nonlinearly with distance. Variability perpendicular to the direction of movement, which results from directional errors, was generally smaller than extent variability, but it increased in proportion to the extent of the movement. Therefore, directional variability, in angular terms, was constant and independent of distance. Because the patterns of variability were similar for both slow and fast movements, as well as for movements involving different joints, we conclude that they result largely from errors in the planning process. We also argue that they cannot be simply explained as consequences of the inertial properties of the limb. Rather they provide evidence for an organizing mechanism that moves the limb along a straight path. We further conclude that reaching movements are planned in a hand-centered coordinate system, with direction and extent of hand movement as the planned parameters. Since the factors which influence directional variability are independent of those that influence extent errors, we propose that these two variables can be separately specified by the brain.

Xist is expressed in female embryonal carcinoma cells with two active X chromosomes

The Xist gene resides on the X chromosome and is expressed in female but not male somatic cells. In female cells, only the Xist allele on the inactive X chromosome is transcribed. We investigated the expression of Xist in diploid P10 female embryonal carcinoma cells that have two active X chromosomes. Xist RNA was present in these P10 cells. The X chromosomes in P10 cells carry different Xist alleles whose transcripts can be distinguished by restriction digestion of their cDNAs. Both alleles were expressed. Clones of P10 cells that had lost an X chromosome did not express Xist from the remaining allele. Thus Xist is expressed in cultured cells developmentally arrested prior to X chromosome inactivation, indicating that the Xist transcript is not always derived from an inactive X chromosome. Therefore, Xist expression per se cannot be a sufficient signal to inactivate an X chromosome.

Protein tyrosine kinases couple the surface immunoglobulin of germinal center B cells to phosphatidylinositol-dependent and -independent pathways of rescue from apoptosis

Considerable progress has been made recently in elucidating the intracellular signal transduction pathways which couple surface immunoglobulin (sIg) of resting B lymphocytes (BH) to the proliferative cycle. By contrast, nothing is known of the signals which couple the sIg of germinal center (GC) B cells not to mitogenesis but, instead, to the suppression of apoptosis: the present study examines the signaling pathways through which this response is achieved. GC B cells treated with anti-Ig exhibited enhanced phosphorylation on tyrosine for a number substrates: this was accompanied by a transient increase in inositol 1,4,5-trisphosphate, an increase in [Ca2+]i, and translocation of PKC from the cytosol. These changes could be provoked with Abs specific for IgG or IgA, the major sIg on GC B cells. Herbimycin A, an inhibitor of protein tyrosine kinases (PTK), uncoupled sIg on GC B cells from both the increase in [Ca2+]i and the rescue from apoptosis: the latter was only partially blocked by inhibitors of PKC and chelators of intracellular and extracellular Ca2+. These data indicate that not only do PTK link the antigen receptor (AgR) of GC B cells to both phosphatidylinositol (PI)-dependent and -independent routes of survival but also that tyrosine phosphorylation is critical for sIg-mediated rescue of this population from apoptosis. Moreover, despite the distinct functional responses observed following ligation of the AgR of resting BH lymphocytes and GC B cells, anti-Ig initiates a very similar pattern of second messenger change in these populations suggesting that bifurcation must occur at a more distal stage of the signaling process.

Antibodies to murine CD40 stimulate normal B lymphocytes but inhibit proliferation of B lymphoma cells

A rat anti-mouse CD40 antiserum has been prepared by hyperimmunisation of Lewis rats with a highly purified preparation of the recombinant extracellular domain of murine CD40. This antiserum specifically binds CD40-expressing L cell transfectants, but not untransfected L cells, and induces vigorous proliferation of highly purified small dense B cells obtained from the spleens of unstimulated mice. Anti-CD40-induced B cell proliferation can be augmented by the addition of IL-4 and is inhibited by purified recombinant soluble mouse CD40. Interestingly the same anti-CD40 antiserum specifically inhibits the in vitro growth of A.20 murine B lymphoma cells. The specificity of this inhibition can be demonstrated by reversing the effect with purified recombinant soluble mouse CD40. These data implicate CD40 as a possible target for therapeutic intervention in the treatment of B lymphomas.

Protein tyrosine phosphorylation is mandatory for CD40-mediated rescue of germinal center B cells from apoptosis

Spontaneous apoptosis in germinal center (GC) B cells can be arrested either by engaging cell surface immunoglobulin (Ig) with immobilized ligand or, more effectively, by treatment with soluble monoclonal antibody (mAb) directed against CD40. The present study examines the intracellular signal transduction pathways through which rescue from spontaneous apoptosis is engendered in GC B cells following ligation of surface CD40. Cross-linking the surface CD40 of GC B cells with mAb consistently resulted in enhanced tyrosine phosphorylation on a number of distinct substrates: this process could be blocked, in a dose-dependent fashion, by pre-treating GC B cells with the selective protein tyrosine kinase(s) (PTK) inhibitor, herbimycin A. Moreover, the pattern of phosphorylation on tyrosine observed following treatment with anti-CD40 was remarkably similar to that triggered by polyvalent anti-Ig. By contrast, anti-CD40 failed to stimulate the increase in inositol 1,4,5-trisphosphate and cytosolic free calcium observed in both GC B cells and resting B lymphocytes following ligation of surface Ig. The involvement of the signaling pathways generated in the rescue of GC B cells from apoptosis was studied by using selective inhibitors of PTK and of extracellular and intracellular Ca2+. Pre-incubation with the PTK inhibitor herbimycin A (5 microM) abrogated anti-CD40-mediated rescue of GC B cells from apoptosis, while genistein (40 microM) and the tyrphostins AG490 (10 microM) and AG814 (25 microM) significantly inhibited this process. Consistent with these results, herbimycin A (5 microM) abolished the expression of the 26 kDa bcl-2 protooncogene product, which confers resistance to apoptosis, normally observed following culture with anti-CD40. The Ca2+ chelators BAPTA and EGTA did not significantly affect CD40-promoted rescue. Taken together, these results indicate that CD40 of GC B cells is coupled to functional PTK but not to the phosphatidylinositol signaling pathway and that tyrosine phosphorylation is mandatory for CD40-mediated rescue of GC B cells from apoptosis.

Inhibition of human neurotropic virus (JCV) DNA replication in glial cells by camptothecin

Progressive multifocal leukoencephalopathy is a subacute demyelinating disease of the central nervous system (CNS) resulting from opportunistic infections in immunocompromised patients infected with a common polyomavirus, JC virus (JCV). Unlike other polyomaviruses, JCV exhibits an unusually narrow tissue tropism by primarily infecting glial cells of the CNS. JCV DNA replication is similar to that of the well-characterized papovavirus, SV40, which requires the viral early protein T-antigen and host-replication factors including DNA polymerases and DNA topoisomerase I. In this study we have been able to effectively block replication of viral DNA in glial cells using camptothecin, a drug which inhibits DNA topoisomerase activity. Pulse-treatment of cells with non-toxic levels of camptothecin specifically blocks viral DNA replication with no inhibitory effect on host transcription and translation processes as examined by viral gene expression in the transfected cells. Furthermore, drug treatment of the cells exhibits no significant effect on DNA topoisomerase I gene transcription. We further demonstrate that repeated pulse-treatment of cells with the drug is required for complete blockage of viral DNA replication. The importance of these findings in the treatment of AIDS encephalopathy is discussed.