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Imaging Polarization in Budding Yeast. - Methods in molecular biology (Clifton, N.J.)
We describe methods for live-cell imaging of yeast cells that we have exploited to image yeast polarity establishment. As a rare event occurring on a fast time-scale, imaging polarization involves a trade-off between spatiotemporal resolution and long-term imaging without excessive phototoxicity. By synchronizing cells in a way that increases resistance to photodamage, we discovered unexpected aspects of polarization including transient intermediates with more than one polarity cluster, oscillatory clustering of polarity factors, and mobile "wandering" polarity sites.
A comparison of regional and national values for recovering threatened and endangered marine species in the United States. - Journal of environmental management
It is generally acknowledged that willingness-to-pay (WTP) estimates for environmental goods exhibit some degree of spatial variation. In a policy context, spatial variation in threatened and endangered species values is important to understand, as the benefit stream from policies affecting threatened and endangered species may vary locally, regionally, or among certain population segments. In this paper we present WTP estimates for eight different threatened and endangered marine species estimated from a stated preference choice experiment. WTP is estimated at two different spatial scales: (a) a random sample of over 5000 U.S. households and (b) geographically embedded samples (relative to the U.S. household sample) of nine U.S. Census regions. We conduct region-to-region and region-to-nation statistical comparisons to determine whether species values differ among regions and between each region and the entire U.S. Our results show limited spatial variation between national values and values estimated from regionally embedded samples, and differences are only found for three of the eight species. More variation exists between regions, and for all species there is a significant difference in at least one region-to-region comparison. Given that policy analyses involving threatened and endangered marine species can often be regional in scope (e.g., ecosystem management) or may disparately affect different regions, our results should be of high interest to the marine management community.Published by Elsevier Ltd.
Sensing a bud in the yeast morphogenesis checkpoint: a role for Elm1. - Molecular biology of the cell
Bud formation by Saccharomyces cerevisiae must be coordinated with the nuclear cycle to enable successful proliferation. Many environmental stresses temporarily disrupt bud formation, and in such circumstances, the morphogenesis checkpoint halts nuclear division until bud formation can resume. Bud emergence is essential for degradation of the mitotic inhibitor, Swe1. Swe1 is localized to the septin cytoskeleton at the bud neck by the Swe1-binding protein Hsl7. Neck localization of Swe1 is required for Swe1 degradation. Although septins form a ring at the presumptive bud site before bud emergence, Hsl7 is not recruited to the septins until after bud emergence, suggesting that septins and/or Hsl7 respond to a "bud sensor." Here we show that recruitment of Hsl7 to the septin ring depends on a combination of two septin-binding kinases: Hsl1 and Elm1. We elucidate which domains of these kinases are needed and show that artificial targeting of those domains suffices to recruit Hsl7 to septin rings even in unbudded cells. Moreover, recruitment of Elm1 is responsive to bud emergence. Our findings suggest that Elm1 plays a key role in sensing bud emergence.Â© 2016 Kang etÂ al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attributionâ€“Noncommercialâ€“Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).
Clinical Conundrum: Killian-Jamieson Diverticulum with Paraesophageal Hernia. - Dysphagia
Killian-Jamieson diverticulum is a outpouching of the lateral cervical esophageal wall adjacent to the insertion of the recurrent laryngeal to the larynx and is much less common in clinical practice than Zenkers Diverticulum. Surgical management of Killian-Jamieson diverticulum requires open transcervical diverticulectomy due to the proximity of the recurrent laryngeal nerve to the base of the pouch. We present a case of a Killian-Jamieson diverticulum associated with a concurrent large type III paraesophageal hernia causing significant solid-food dysphagia, post-prandial regurgitation of solid foods, and chronic cough managed with open transcervical diverticulectomy and laparoscopic paraesophageal hernia repair with Nissen fundoplication.
Role of Polarized G Protein Signaling in Tracking Pheromone Gradients. - Developmental cell
Yeast cells track gradients of pheromones to locate mating partners. Intuition suggests that uniform distribution of pheromone receptors over the cell surface would yield optimal gradient sensing. However, yeast cells display polarized receptors. The benefit of such polarization was unknown. During gradient tracking, cell growth is directed by a patch of polarity regulators that wanders around the cortex. Patch movement is sensitive to pheromone dose, with wandering reduced on the up-gradient side of the cell, resulting in net growth in that direction. Mathematical modeling suggests that active receptors and associated G proteins lag behind the polarity patch and act as an effective drag on patch movement. In vivo, the polarity patch is trailed by a G protein-rich domain, and this polarized distribution of G proteins is required to constrain patch wandering. Our findings explain why G protein polarization is beneficial and illuminate a novel mechanism for gradient tracking.Copyright Â© 2015 Elsevier Inc. All rights reserved.
Role of competition between polarity sites in establishing a unique front. - eLife
Polarity establishment in many cells is thought to occur via positive feedback that reinforces even tiny asymmetries in polarity protein distribution. Cdc42 and related GTPases are activated and accumulate in a patch of the cortex that defines the front of the cell. Positive feedback enables spontaneous polarization triggered by stochastic fluctuations, but as such fluctuations can occur at multiple locations, how do cells ensure that they make only one front? In polarizing cells of the model yeast Saccharomyces cerevisiae, positive feedback can trigger growth of several Cdc42 clusters at the same time, but this multi-cluster stage rapidly evolves to a single-cluster state, which then promotes bud emergence. By manipulating polarity protein dynamics, we show that resolution of multi-cluster intermediates occurs through a greedy competition between clusters to recruit and retain polarity proteins from a shared intracellular pool.
Diabetic foot infections: what have we learned in the last 30 years? - International journal of infectious diseases : IJID : official publication of the International Society for Infectious Diseases
Infection is a common epiphenomenon of advanced diabetic foot disease and the most common reason for diabetes-related hospitalizations and lower extremity amputations. Major advances have been made in the past three decades in our understanding and management of diabetic foot infections (DFIs). The optimal treatment of DFIs clearly involves multidisciplinary input.A comprehensive search of the literature on DFIs from January 1960 through June 2015 was performed, with an emphasis on information published in the past 30 years.There have been many new insights into the microbiology, diagnosis, and treatment of DFIs, although the implementation of this knowledge in clinical practice has been suboptimal. Today, the use of evidence-based guidelines, multidisciplinary teams, and institution-specific clinical pathways helps guide optimal care of this multifaceted problem. Patients are more often treated in the ambulatory setting, with antibiotic regimens that are more targeted, oral and shorter course, and with more conservative (but earlier) surgical interventions. New diagnostic and therapeutic methods are being developed at an accelerating pace.The worldwide increase in the incidence of diabetes and longer lifespan of diabetic patients will undoubtedly increase the incidence of DFIs. Clinicians caring for diabetic patients should have an understanding of current methods for preventing, diagnosing, and treating DFIs.Copyright Â© 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.
Polarity establishment requires localized activation of Cdc42. - The Journal of cell biology
Establishment of cell polarity in animal and fungal cells involves localization of the conserved Rho-family guanosine triphosphatase, Cdc42, to the cortical region destined to become the "front" of the cell. The high local concentration of active Cdc42 promotes cytoskeletal polarization through various effectors. Cdc42 accumulation at the front is thought to involve positive feedback, and studies in the budding yeast Saccharomyces cerevisiae have suggested distinct positive feedback mechanisms. One class of mechanisms involves localized activation of Cdc42 at the front, whereas another class involves localized delivery of Cdc42 to the front. Here we show that Cdc42 activation must be localized for successful polarity establishment, supporting local activation rather than local delivery as the dominant mechanism in this system.Â© 2015 Woods et al.
Dendritic spine geometry can localize GTPase signaling in neurons. - Molecular biology of the cell
Dendritic spines are the postsynaptic terminals of most excitatory synapses in the mammalian brain. Learning and memory are associated with long-lasting structural remodeling of dendritic spines through an actin-mediated process regulated by the Rho-family GTPases RhoA, Rac, and Cdc42. These GTPases undergo sustained activation after synaptic stimulation, but whereas Rho activity can spread from the stimulated spine, Cdc42 activity remains localized to the stimulated spine. Because Cdc42 itself diffuses rapidly in and out of the spine, the basis for the retention of Cdc42 activity in the stimulated spine long after synaptic stimulation has ceased is unclear. Here we model the spread of Cdc42 activation at dendritic spines by means of reaction-diffusion equations solved on spine-like geometries. Excitable behavior arising from positive feedback in Cdc42 activation leads to spreading waves of Cdc42 activity. However, because of the very narrow neck of the dendritic spine, wave propagation is halted through a phenomenon we term geometrical wave-pinning. We show that this can account for the localization of Cdc42 activity in the stimulated spine, and, of interest, retention is enhanced by high diffusivity of Cdc42. Our findings are broadly applicable to other instances of signaling in extreme geometries, including filopodia and primary cilia.Â© 2015 Ramirez etÂ al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attributionâ€“Noncommercialâ€“Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).
To avoid a mating mishap, yeast focus and communicate. - The Journal of cell biology
During mating, yeast cells must perforate their rigid cell walls at the right place to allow cell-cell fusion. In this issue, Dudin et al. (2015; J. Cell Biol. http://dx.doi.org/jcb.201411124) image mating fission yeast cells with unprecedented spatiotemporal resolution. The authors find that when mating cells come into contact, they form aster-like actin structures that direct cell wall remodeling precisely to the point of contact.Â© 2015 McClure and Lew.
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