RESUMO
Dendrite microtubules are polarized with minus-end-out orientation in Drosophila neurons. Nucleation sites concentrate at dendrite branch points, but how they localize is not known. Using Drosophila, we found that canonical Wnt signaling proteins regulate localization of the core nucleation protein γTubulin (γTub). Reduction of frizzleds (fz), arrow (low-density lipoprotein receptor-related protein [LRP] 5/6), dishevelled (dsh), casein kinase Iγ, G proteins, and Axin reduced γTub-green fluorescent protein (GFP) at branch points, and two functional readouts of dendritic nucleation confirmed a role for Wnt signaling proteins. Both dsh and Axin localized to branch points, with dsh upstream of Axin. Moreover, tethering Axin to mitochondria was sufficient to recruit ectopic γTub-GFP and increase microtubule dynamics in dendrites. At dendrite branch points, Axin and dsh colocalized with early endosomal marker Rab5, and new microtubule growth initiated at puncta marked with fz, dsh, Axin, and Rab5. We propose that in dendrites, canonical Wnt signaling proteins are housed on early endosomes and recruit nucleation sites to branch points.
Assuntos
Dendritos/metabolismo , Proteínas de Drosophila/metabolismo , Endossomos/metabolismo , Microtúbulos/metabolismo , Proteínas Wnt/metabolismo , Animais , Complexo de Sinalização da Axina/genética , Complexo de Sinalização da Axina/metabolismo , Axônios/metabolismo , Polaridade Celular , Dendritos/genética , Drosophila , Proteínas de Drosophila/genética , Endossomos/genética , Microtúbulos/genética , Mutação , Receptores Wnt/genética , Receptores Wnt/metabolismo , Tubulina (Proteína)/genética , Tubulina (Proteína)/metabolismo , Proteínas Wnt/genética , Via de Sinalização Wnt/genética , Proteínas rab5 de Ligação ao GTP/genética , Proteínas rab5 de Ligação ao GTP/metabolismoRESUMO
BACKGROUND: Autoimmune voltage-gated potassium channelopathies have been associated with a range of neurological presenting symptoms, including central, peripheral, and autonomic dysfunction. PATIENT DESCRIPTION: We describe a 12-year-old boy who presented with nine months of pain, anxiety, and 30-pound weight loss. He was admitted for failure to thrive, then noted to be persistently hypertensive and tachycardic. Plasma metanephrines and urine metanephrines and catecholamines were elevated. Extensive investigation for causes of elevated catecholamines, such as hyperthyroidism or catecholamine-secreting tumor, was negative. A paraneoplastic panel was positive for voltage-gated potassium channel antibodies. Treatment with intravenous immunoglobulin and pulse methylprednisolone led to complete resolution of symptoms, weight gain, and normalization of vital signs and plasma metanephrines. CONCLUSION: Voltage-gated potassium channel antibodies should be considered as part of the differential in patients presenting with elevated metanephrine and catecholamine secretion.
Assuntos
Autoanticorpos/sangue , Catecolaminas/urina , Canalopatias/imunologia , Metanefrina/metabolismo , Canais de Potássio de Abertura Dependente da Tensão da Membrana/imunologia , Canalopatias/metabolismo , Criança , Humanos , Masculino , Metanefrina/sangue , Metanefrina/urinaRESUMO
Axon regeneration allows neurons to repair circuits after trauma; however, most of the molecular players in this process remain to be identified. Given that microtubule rearrangements have been observed in injured neurons, we tested whether microtubule-severing proteins might play a role in axon regeneration. We found that axon regeneration is extremely sensitive to levels of the microtubule-severing protein spastin. Although microtubule behavior in uninjured neurons was not perturbed in animals heterozygous for a spastin null allele, axon regeneration was severely disrupted in this background. Two types of axon regeneration-regeneration of an axon from a dendrite after proximal axotomy and regeneration of an axon from the stump after distal axotomy-were defective in Drosophila with one mutant copy of the spastin gene. Other types of axon and dendrite outgrowth, including regrowth of dendrites after pruning, were normal in heterozygotes. We conclude that regenerative axon growth is uniquely sensitive to spastin gene dosage.