Purification and characterization of an acid metalloproteinase from human articular cartilage

A metalloprotease that digests cartilage proteoglycan optimally at pH 5.3 has been purified (4400-fold) to homogeneity from 20-g samples of human articular cartilage containing about 100 micrograms of enzyme. This enzyme was cleanly separated from a related neutral metalloprotease with an optimum pH of 7.2. The acid metalloprotease displays 40% of its maximum activity at pH 7.2 and so has significant activity at physiological pH. The protease is calcium-dependent and indirect evidence suggests that it may contain zinc at its active center. It occurs largely in a latent form that can be activated by aminophenylmercuric acetate. The apparent Mr of the latent form is 55,000 and of the active form, 35,000. The isoelectric point is at pH 4.9. The protease activity is inhibited by chelators, Z-phenylalanine, ovostatin, and tissue inhibitor of metalloproteinase from human articular cartilage. It differs from metalloproteinases such as enkephalinase and kidney brush-border protease in its failure to be strongly inhibited by phosphoramidon and Zincov. It cleaves the proteoglycan monomer of bovine nasal cartilage to fragments of approximately 140,000 Da. It cleaves the B chain of insulin at Ala14-Leu15 and Tyr16-Leu17. A survey of 26 cartilage extracts indicates this enzyme is elevated to about 3 times the normal level in human osteoarthritic cartilage and that the tissue inhibitor of metalloproteinase is only slightly diminished. Preliminary evidence points to the presence of a similar acid metalloprotease activity in human polymorphonuclear leukocytes.     

Nuclear envelope‐associated dynein drives prophase centrosome separation and enables Eg5‐independent bipolar spindle formation

The microtubule motor protein kinesin‐5 (Eg5) provides an outward force on centrosomes, which drives bipolar spindle assembly. Acute inhibition of Eg5 blocks centrosome separation and causes mitotic arrest in human cells, making Eg5 an attractive target for anti‐cancer therapy. Using in vitro directed evolution, we show that human cells treated with Eg5 inhibitors can rapidly acquire the ability to divide in the complete absence of Eg5 activity. We have used these Eg5‐independent cells to study alternative mechanisms of centrosome separation. We uncovered a pathway involving nuclear envelope (NE)‐associated dynein that drives centrosome separation in prophase. This NE‐dynein pathway is essential for bipolar spindle assembly in the absence of Eg5, but also functions in the presence of full Eg5 activity, where it pulls individual centrosomes along the NE and acts in concert with Eg5‐dependent outward pushing forces to coordinate prophase centrosome separation. Together, these results reveal how the forces are produced to drive prophase centrosome separation and identify a novel mechanism of resistance to kinesin‐5 inhibitors.     

A physiological analogy of the niche for projecting the potential distribution of plants

Aim  To develop a physiologically based model of the plant niche for use in species distribution modelling. Location  Europe. Methods  We link the Thornley transport resistance (TTR) model with functions which describe how the TTR’s model parameters are influenced by abiotic environmental factors. The TTR model considers how carbon and nutrient uptake, and the allocation of these assimilates, influence growth. We use indirect statistical methods to estimate the model parameters from a high resolution data set on tree distribution for 22 European tree species. Results  We infer, from distribution data and abiotic forcing data, the physiological niche dimensions of 22 European tree species. We found that the model fits were reasonable (AUC: 0.79–0.964). The projected distributions were characterized by a false positive rate of 0.19 and a false negative rate 0.12. The fitted models are used to generate projections of the environmental factors that limit the range boundaries of the study species. Main conclusions  We show that physiological models can be used to derive physiological niche dimensions from species distribution data. Future work should focus on including prior information on physiological rates into the parameter estimation process. Application of the TTR model to species distribution modelling suggests new avenues for establishing explicit links between distribution and physiology, and for generating hypotheses about how ecophysiological processes influence the distribution of plants.     

A simple integrative electrophysiological model of bursting GnRH neurons

In this paper a modular model of the GnRH neuron is presented. For the aim of simplicity, the currents corresponding to fast time scales and action potential generation are described by an impulsive system, while the slower currents and calcium dynamics are described by usual ordinary differential equations (ODEs). The model is able to reproduce the depolarizing afterpotentials, afterhyperpolarization, periodic bursting behavior and the corresponding calcium transients observed in the case of GnRH neurons.