Echocardiogram: The GPS to GPA's Heart (Granulomatosis with Polyangiitis).

Granulomatosis with polyangiitis (GPA) is a rare ANCA-associated necrotizing granulomatous vasculitis affecting small- to medium-sized vessels. Common manifestations of this disease process affect the ear, nose, throat, upper and lower airways, and kidneys. Cardiac involvement has been reported in 6-44% of patients, primarily as coronary arteritis and pericarditis. A majority of case reports of pericardial effusions in patients with GPA identify patients having constrictive pericarditis secondary to uremia. We are presenting a case of hemorrhagic pericarditis in a patient with GPA in which the underlying inflammatory vasculitis likely played the primary role in the patient's presentation. Echocardiographic abnormalities have been found in 80% of patients with GPA. Given the high mortality from cardiac involvement in patients with GPA, screening echocardiograms for this patient population may serve as a helpful tool in gauging disease severity, thereby guiding therapy to prevent serious cardiac complications, such as cardiac tamponade as presented in this case report.

Development of dendrite polarity in Drosophila neurons.

BACKGROUND: Drosophila neurons have dendrites that contain minus-end-out microtubules. This microtubule arrangement is different from that of cultured mammalian neurons, which have mixed polarity microtubules in dendrites. RESULTS: To determine whether Drosophila and mammalian dendrites have a common microtubule organization during development, we analyzed microtubule polarity in Drosophila dendritic arborization neuron dendrites at different stages of outgrowth from the cell body in vivo. As dendrites initially extended, they contained mixed polarity microtubules, like mammalian neurons developing in culture. Over a period of several days this mixed microtubule array gradually matured to a minus-end-out array. To determine whether features characteristic of dendrites were localized before uniform polarity was attained, we analyzed dendritic markers as dendrites developed. In all cases the markers took on their characteristic distribution while dendrites had mixed polarity. An axonal marker was also quite well excluded from dendrites throughout development, although this was perhaps more efficient in mature neurons. To confirm that dendrite character could be acquired in Drosophila while microtubules were mixed, we genetically disrupted uniform dendritic microtubule organization. Dendritic markers also localized correctly in this case. CONCLUSIONS: We conclude that developing Drosophila dendrites initially have mixed microtubule polarity. Over time they mature to uniform microtubule polarity. Dendrite identity is established before the mature microtubule arrangement is attained, during the period of mixed microtubule polarity.

Directed microtubule growth, +TIPs, and kinesin-2 are required for uniform microtubule polarity in dendrites.

BACKGROUND: in many differentiated cells, microtubules are organized into polarized noncentrosomal arrays, yet few mechanisms that control these arrays have been identified. For example, mechanisms that maintain microtubule polarity in the face of constant remodeling by dynamic instability are not known. Drosophila neurons contain uniform-polarity minus-end-out microtubules in dendrites, which are often highly branched. Because undirected microtubule growth through dendrite branch points jeopardizes uniform microtubule polarity, we have used this system to understand how cells can maintain dynamic arrays of polarized microtubules. RESULTS: we find that growing microtubules navigate dendrite branch points by turning the same way, toward the cell body, 98% of the time and that growing microtubules track along stable microtubules toward their plus ends. Using RNAi and genetic approaches, we show that kinesin-2, and the +TIPS EB1 and APC, are required for uniform dendrite microtubule polarity. Moreover, the protein-protein interactions and localization of Apc2-GFP and Apc-RFP to branch points suggests that these proteins work together at dendrite branches. The functional importance of this polarity mechanism is demonstrated by the failure of neurons with reduced kinesin-2 to regenerate an axon from a dendrite. CONCLUSIONS: we conclude that microtubule growth is directed at dendrite branch points and that kinesin-2, APC, and EB1 are likely to play a role in this process. We propose that kinesin-2 is recruited to growing microtubules by +TIPS and that the motor protein steers growing microtubules at branch points. This represents a newly discovered mechanism for maintaining polarized arrays of microtubules.