Faculty Bibliography

Electron cryomicroscopy of rotor complexes of the Salmonella typhimurium flagellar motor, overproduced in a nonmotile Escherichia coli host, has revealed a variation in subunit symmetry of the cytoplasmic ring (C ring) module. C rings with subunit symmetries ranging from 31 to 38 were found. They formed a Gaussian distribution around a mean between 34 and 35, a similar number to that determined for native C rings. C-ring diameter scaled with the number of subunits, indicating that the elliptical-shaped subunits maintained constant intersubunit spacing. Taken together with evidence that the M ring does not correspondingly increase in size, this finding indicates that rotor assembly does not require strict stoichiometric interactions between the M- and C-ring subunits. Implications for motor function are discussed.

Wounding skin generates an endogenous electric field of 100-200 mV/mm in the immediate vicinity of the wound. When keratinocytes are exposed to direct current electric fields of this magnitude, they exhibit galvanotaxis, or directional migration toward the cathode, suggesting that wound-generated electric fields provide migrational cues that contribute to wound healing. Because melanocytes must also migrate into the healing wound to repigment it, their motility in response to electric fields of physiologic magnitude was examined. Human skin-derived melanocytes, either exposed to 100 mV/mm direct current electric fields or nonexposed controls, both exhibited motility rates of 9 micro m/hour, significantly (three- to five-fold) lower than the motility rates of keratinocytes under identical conditions. However, in sharp contrast to keratinocytes, melanocytes exhibited no directional migration in the electric field. Additionally, neither the number of primary dendrites per cell, nor the orientation of the dendrites with respect to the field vector, nor the average length of the dendrites was significantly different in melanocytes exposed to the electric field as compared to nonexposed controls. Thus, in marked contrast to keratinocytes, human skin-derived melanocytes do not respond to direct current electric fields of physiologic magnitude with either directional migration or reorientation of dendrites. This may account for the delay in repigmentation that often accompanies wound reepithelialization

glp-1 encodes a member of the highly conserved LIN-12/Notch family of receptors that mediates the mitosis/meiosis decision in the C. elegans germline. We have characterized three mutations that represent a new genetic and phenotypic class of glp-1 mutants, glp-1(Pro). The glp-1(Pro) mutants display gain-of-function germline pattern defects, most notably a proximal proliferation (Pro) phenotype. Each of three glp-1(Pro) alleles encodes a single amino acid change in the extracellular part of the receptor: two in the LIN-12/Notch repeats (LNRs) and one between the LNRs and the transmembrane domain. Unlike other previously described gain-of-function mutations that affect this region of LIN-12/Notch family receptors, the genetic behavior of glp-1(Pro) alleles is not consistent with simple hypermorphic activity. Instead, the mutant phenotype is suppressed by wild-type doses of glp-1. Moreover, a trans-heterozygous combination of two highly penetrant glp-1(Pro) mutations is mutually suppressing. These results lend support to a model for a higher-order receptor complex and/or competition among receptor proteins for limiting factors that are required for proper regulation of receptor activity. Double-mutant analysis with suppressors and enhancers of lin-12 and glp-1 further suggests that the functional defect in glp-1(Pro) mutants occurs prior to or at the level of ligand interaction

We collaborate in a research program aimed at creating a rigorous framework, experimental infrastructure, and computational environment for understanding, experimenting with, manipulating, and modifying a diverse set of fundamental biological processes at multiple scales and spatio-temporal modes. The novelty of our research is based on an approach that (i) requires coevolution of experimental science and theoretical techniques and (ii) exploits a certain universality in biology guided by a parsimonious model of evolutionary mechanisms operating at the genomic level and manifesting at the proteomic, transcriptomic, phylogenic, and other higher levels. Our current program in 'systems biology' endeavors to marry large-scale biological experiments with the tools to ponder and reason about large, complex, and subtle natural systems. To achieve this ambitious goal, ideas and concepts are combined from many different fields: biological experimentation, applied mathematical modeling, computational reasoning schemes, and large-scale numerical and symbolic simulations. From a biological viewpoint, the basic issues are many: (i) understanding common and shared structural motifs among biological processes; (ii) modeling biological noise due to interactions among a small number of key molecules or loss of synchrony; (iii) explaining the robustness of these systems in spite of such noise; and (iv) cataloging multistatic behavior and adaptation exhibited by many biological processes

There are several options available for management of the middle-aged arthritic knee. Arthroscopic techniques continue to evolve, but the true natural history of the arthritic process is probably not altered. Good to excellent short-term results can be expected with proper patient selection. Patient counseling is important in order to discuss the nature of the underlying disease process, the limited goals of the arthroscopic procedure, and the possible need for further surgery. Proximal tibial osteotomy for the treatment of medial compartment osteoarthritis can be effective for as long as 15 years. There is a deterioration of results over time that can often be correlated to the degree of correction achieved. Strict selection criteria can maximize success. Revision surgery to total knee replacement, albeit technically difficult, is a viable option with results similar to primary TKR. Unicompartmental knee arthroplasty remains a controversial procedure as its indications continue to evolve. Good to excellent results can be expected in 80% to 90% of patients at 10 years follow-up. Unicompartmental knee arthroplasty occupies a special niche in the treatment of unicompartmental osteoarthritis and supplements total knee replacement and high tibial osteotomy surgery

Both static and dynamic loads were applied to metal-backed acetabular cups with ceramic or polyethylene inserts and the resulting load transmissions at a simulated bone interface were determined. Perfect fit and under-sized and over-sized cavities were prepared in simulated bone substrates, lined with Fuji pressure sensitive film, and acetabular cups inserted with physiological loads. The magnitude and location of contact forces between the cup and bone were measured. These cups were then subjected to a controlled impact load and the intensity and frequency of the loads transmitted to the substrate were determined. The results suggest that a polyethylene backing for ceramics is not necessary as there were no major differences in the static and dynamic stresses transmitted to the cup-bone interface with all polyethylene or ceramic inserts

Introduccion y objetivos. Se sabe que el consumo de fitosteroles reduce la concentracion de colesterol en plasma, debido a la interferencia de estos compuestos en la absorcion intestinal de colesterol. Aunque en pequena proporcion, los fitosteroles de la dieta tambien se asimilan, y su concentracion en el plasma es mil veces inferior a la del colesterol. Dada su analogia estructural con el colesterol, nos planteamos determinar el efecto de distintos fitosteroles sobre la biosintesis de colesterol en celulas humanas y su repercusion sobre la proliferacion celular. Metodo. Las celulas de la linea promielocitica humana HL-60 se cultivaron en un medio libre de colesterol (DCCM-l) en presencia de los diferentes esteroles en estudio y de [14C]-acetato como precursor para la biosintesis de colesterol. Al cabo de 8 h de incubacion se lisaron las celulas y se extrajeron los lipidos no saponificables, que posteriormente fueron analizados mediante cromatografia liquida de alta resolucion (HPLC). La proliferacion celular se analizo determinando la incorporacion de [3H]-timidina al ADN y por recuento de las celulas. Resultados. Los fitosteroles insaturados en el C22 de la cadena lateral-estigmasterol, brasicasterol y ergosterol- inhibieron la biosintesis de colesterol en celulas HL-60 en concentraciones fisiologicas, de 1 µg/ml, mientras que los otros fitosteroles-ß-sitosterol y campesterol- fueron inactivos incluso en concentraciones de 30 µg/ml. El 5, 22-colestadien-3ß-ol, un esterol no natural que contiene tambien un doble enlace en C22, inhibio la incorporacion de [14C]-acetato a colesterol mucho mas intensamente que los anteriores. El descenso de 14C-colesterol se acompano de un aumento de la radiactividad en desmosterol y tambien, aunque menos intensamente, en 5, 7, 24-colestatrien-3ß-ol. A pesar de estos cambios en la composicion celular de esteroles, los fitosteroles no afectaron la viabilidad ni la proliferacion de las celulas HL-60, lo que sugiere que los esteroles intermediarios pueden suplir al colesterol en sus funciones en la division celular. Conclusiones. Los fitosteroles con doble enlace en C22 inhiben la biosintesis de colesterol a valor de la esterol delta24-reductasa en concentraciones que pueden considerarse fisiologicas, por lo que esta accion puede considerarse un mecanismo adicional para explicar los efectos hipolipemiantes de estos compuestos