945 research outputs found
Wave propagation and cell movement control morphogenesis of the cellular slime mould Dictyostelium discoideum
Three-dimensional waves of excitation during Dictyostelium morphogenesis
Cells in Dictyostelium slugs follow well-defined patterns of motion. We found that the chemotactic cell response is controlled by a scroll wave of messenger concentration in the highly excitable prestalk zone of the slug that decays in the less-excitable prespore region into planar wave fronts. This phenomenon is investigated by numerical solutions of partial differential equations that couple local nonlinear kinetics and diffusive transport of the chemotactic signal. In the interface of both regions a complex twisted scroll wave is formed that reduces the wave frequency in the prespore zone. The spatio-temporal dynamics of waves and filaments are followed over 33 periods of rotation. These results yield an explanation of collective self-organized cell motion in a multicellular organism
Accommodating quality and service improvement research within existing ethical principles
Funds were provided by a Canadian Institute of Health Research grant (Nominated PI: Monica Taljaard, PJT – 153045). Funds were also generously provided by Charles Weijer, who is funded by a Tier 1 Canadian Research Chair.Peer reviewedPublisher PD
Spatial Pattern Formation During Aggregation of the Slime Mould Dictyostelium discoideum
Stream formation and spiral wave behaviour during the aggregation of Dictyostelium discoideum (Dd)
are studied in a model based on the Martiel-Goldbeter equations for cAMP relay, combined with
chemotactic motion of Dd cells. The results show that stream formation occurs if the turnover rate of
intracellular cAMP is increased. This increase in the turnover rate of cAMP[in] leads to a dependence
of the speed of the cAMP wave on the cell density. We propose that this dependence of wave speed
on cell density is the underlying mechanism for stream formation. Besides stream formation, increasing
the turnover rate of cAMP[in] also results in a spiral wave period that decreases during aggregation, a
phenomenon that is commonly observed in situ.
Furthermore, the dependence of wave speed on cell density is measured empirically[ The speed of
the cAMP wave is found to decrease as the wave travels from high to low cell density. This indicates
that in situ, wave speed does depend on cell density
Coupled Oscillators with Chemotaxis
A simple coupled oscillator system with chemotaxis is introduced to study
morphogenesis of cellular slime molds. The model successfuly explains the
migration of pseudoplasmodium which has been experimentally predicted to be
lead by cells with higher intrinsic frequencies. Results obtained predict that
its velocity attains its maximum value in the interface region between total
locking and partial locking and also suggest possible roles played by partial
synchrony during multicellular development.Comment: 4 pages, 5 figures, latex using jpsj.sty and epsf.sty, to appear in
J. Phys. Soc. Jpn. 67 (1998
Impact of CONSORT extension for cluster randomised trials on quality of reporting and study methodology : review of random sample of 300 trials, 2000-8
Peer reviewedPublisher PD
Screening, intervention and outcome in autism and other developmental disorders: the role of randomized controlled trials
We draw attention to a number of important considerations in the arguments about screening and outcome of intervention in children with autism and other developmental disorders. Autism screening in itself never provides a final clinical diagnosis, but may well identify developmental deviations indicative of autism—or of other developmental disorders—that should lead to referral for further clinical assessment. Decisions regarding population or clinic screening cannot be allowed to be based on the fact that prospective longitudinal RCT designs over decades could never be performed in complex developmental disorders. We propose an alternative approach. Early screening for autism and other developmental disorders is likely to be of high societal importance and should be promoted and rigorously evaluated
Inadequate reporting of research ethics review and informed consent in cluster randomized trials : review of random sample of published trials
Peer reviewedPublisher PD
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