The UNC-45 Chaperone Is Critical for Establishing Myosin-Based Myofibrillar Organization and Cardiac Contractility in the Drosophila Heart Model

UNC-45 is a UCS (UNC-45/CRO1/She4P) class chaperone necessary for myosin folding and/or accumulation, but its requirement for maintaining cardiac contractility has not been explored. Given the prevalence of myosin mutations in eliciting cardiomyopathy, chaperones like UNC-45 are likely to be equally critical in provoking or modulating myosin-associated cardiomyopathy. Here, we used the Drosophila heart model to examine its role in cardiac physiology, in conjunction with RNAi-mediated gene silencing specifically in the heart in vivo. Analysis of cardiac physiology was carried out using high-speed video recording in conjunction with movement analysis algorithms. unc-45 knockdown resulted in severely compromised cardiac function in adults as evidenced by prolonged diastolic and systolic intervals, and increased incidence of arrhythmias and extreme dilation; the latter was accompanied by a significant reduction in muscle contractility. Structural analysis showed reduced myofibrils, myofibrillar disarray, and greatly decreased cardiac myosin accumulation. Cardiac unc-45 silencing also dramatically reduced life-span. In contrast, third instar larval and young pupal hearts showed mild cardiac abnormalities, as severe cardiac defects only developed during metamorphosis. Furthermore, cardiac unc-45 silencing in the adult heart (after metamorphosis) led to less severe phenotypes. This suggests that UNC-45 is mostly required for myosin accumulation/folding during remodeling of the forming adult heart. The cardiac defects, myosin deficit and decreased life-span in flies upon heart-specific unc-45 knockdown were significantly rescued by UNC-45 over-expression. Our results are the first to demonstrate a cardiac-specific requirement of a chaperone in Drosophila, suggestive of a critical role of UNC-45 in cardiomyopathies, including those associated with unfolded proteins in the failing human heart. The dilated cardiomyopathy phenotype associated with UNC-45 deficiency is mimicked by myosin knockdown suggesting that UNC-45 plays a crucial role in stabilizing myosin and possibly preventing human cardiomyopathies associated with functional deficiencies of myosin

Urban nuclei and the geometry of streets : the 'emergent neighborhoods' model

A controversy remains among planners and urban designers about the proper location of the non-residential core (nucleus) of a neighborhood in relation to thoroughfares. One school of thought suggests that the nucleus should be located along the busiest thoroughfares; a second school holds that it must be some distance away from them - which, because of their disruptiveness, should form the edge of the neighborhood; and a third school proposes that it should be somewhere between the two as an 'eccentric nucleus'. The three schools may be overlooking the underlying variables that govern this problem under different conditions, and so we propose a model for establishing the best location and distribution of urban nuclei as these conditions vary. This requires firstly, a redefinition of the 'neighborhood' as distinguished from a 'pedestrian shed'. We argue that a 'neighborhood' can either emerge within a 'sanctuary area' between thoroughfares, or span across both 'sanctuary areas' and thoroughfares, if the latter are properly designed; a 'pedestrian shed', by contrast, can overlap with neighborhoods and with other pedestrian sheds. We propose a '400 meter rule', a surprisingly small maximum spacing of main thoroughfares that empirical observation shows that traditional, pedestrian-governed urban fabric has always tended to obey, for reasons that are likely to have to do with the self-organizing logic of pedestrian movement and social activity. In so doing, we advance a more fine-grained, permeable, potentially lower-carbon model and illustrate its advantages with several historic and modern examples