Biomedical subjects

M C Abraham

Publications and source records attributed to M C Abraham.

3 recordsLinked to original sources

PubMed2001

CDC-42 controls early cell polarity and spindle orientation in C. elegans.

BACKGROUND: Generation of asymmetry in the one-cell embryo of C. elegans establishes the anterior--posterior axis (A-P), and is necessary for the proper identity of early blastomeres. Conserved PAR proteins are asymmetrically distributed and are required for the generation of this early asymmetry. The small G protein Cdc42 is a key regulator of polarity in other systems, and recently it has been shown to interact with the mammalian homolog of PAR-6. The function of Cdc42 in C. elegans had not yet been investigated, however. RESULTS: Here, we show that C. elegans cdc-42 plays an essential role in the polarity of the one-cell embryo and the proper localization of PAR proteins. Inhibition of cdc-42 using RNA interference results in embryos with a phenotype that is nearly identical to par-3, par-6, and pkc-3 mutants, and asymmetric localization of these and other PAR proteins is lost. We further show that C. elegans CDC-42 physically interacts with PAR-6 in a yeast two-hybrid system, consistent with data on the interaction of human homologs. CONCLUSIONS: Our results show that CDC-42 acts in concert with the PAR proteins to control the polarity of the C. elegans embryo, and provide evidence that the interaction of CDC-42 and the PAR-3/PAR-6/PKC-3 complex has been evolutionarily conserved as a functional unit.

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PubMed2001

Scarred patterns in surface waves.

Surface wave patterns are investigated experimentally in a system geometry that has become a paradigm of quantum chaos: the stadium billiard. Linear waves in bounded geometries for which classical ray trajectories are chaotic are known to give rise to scarred patterns. Here, we utilize parametrically forced surface waves (Faraday waves), which become progressively nonlinear beyond the wave instability threshold, to investigate the subtle interplay between boundaries and nonlinearity. Only a subset (three main types) of the computed linear modes of the stadium are observed in a systematic scan. These correspond to modes in which the wave amplitudes are strongly enhanced along paths corresponding to certain periodic ray orbits. Many other modes are found to be suppressed, in general agreement with a prediction by Agam and Altshuler based on boundary dissipation and the Lyapunov exponent of the associated orbit. Spatially asymmetric or disordered (but time-independent) patterns are also found even near onset. As the driving acceleration is increased, the time-independent scarred patterns persist, but in some cases transitions between modes are noted. The onset of spatiotemporal chaos at higher forcing amplitude often involves a nonperiodic oscillation between spatially ordered and disordered states. We characterize this phenomenon using the concept of pattern entropy. The rate of change of the patterns is found to be reduced as the state passes temporarily near the ordered configurations of lower entropy. We also report complex but highly symmetric (time-independent) patterns far above onset in the regime that is normally chaotic.

Journal Article↗

PubMed1996

Inducible immunity to Trichomonas vaginalis in a mouse model of vaginal infection.

We studied the protective effect of subcutaneous immunization with Trichomonas vaginalis in a mouse model of vaginal infection. BALB/c mice were immunized with various doses of T. vaginalis (4.5 x 10(5), 9 x 10(6), and 1 x 10(8) organisms per ml) suspended in Freund's complete adjuvant 56 days prior to vaginal infection and were given booster injections of the same doses of T. vaginalis in Freund's incomplete adjuvant 4 weeks later. Control mice were immunized and given booster injections of phosphate-buffered saline suspended in Freund's complete and incomplete adjuvants. The mice were tail bled and vaginal washes were performed at weekly intervals for 4 weeks to determine the isolation of T. vaginalis and the serum and vaginal antibody reactivity. Mice which had been immunized and given booster immunizations had significantly fewer intravaginal infections and had increased serum and vaginal antibody responses compared with those of control mice (P < 0.01). Mice that were vaginally infected, treated with metronidazole, and then reinfected vaginally did not develop protective immunity. Subcutaneous immunization with whole T. vaginalis organisms appears to confer protection against intravaginal challenge with T. vaginalis, protection which is not achieved as a result of prior vaginal infection.

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