Microtubule-severing protein Katanin regulates neuromuscular junction development and dendritic elaboration in Drosophila

Abstract

Microtubules (MTs) are crucial for diverse biological processes including cell division, cell growth and motility, intracellular transport and the maintenance of cell shape. MT abnormalities are associated with neurodevelopmental and neurodegenerative diseases such as hereditary spastic paraplegia. Among many MT regulators, katanin was the first identified MT-severing protein, but its neuronal functions have not yet been examined in a multicellular organism. Katanin consists of two subunits; the catalytic subunit katanin 60 contains an AAA (ATPases associated with a variety of cellular activities) domain and breaks MT fibers while hydrolyzing ATP, whereas katanin 80 is a targeting and regulatory subunit. To dissect the in vivo functions of Katanin, we generated mutations in Drosophila Katanin 60 and manipulated its expression in a tissue-specific manner. Null mutants of Katanin 60 are pupal lethal, demonstrating that it is essential for viability. Loss-of-function mutants of Katanin 60 showed excess satellite boutons, reduced neurotransmission efficacy, and more enlarged cisternae at neuromuscular junctions. In peripheral sensory neurons, loss of Katanin 60 led to increased elaboration of dendrites, whereas overexpression of Katanin 60 resulted in the opposite. Genetic interaction analyses indicated that increased levels of MT acetylation increase its susceptibility to Katanin-mediated severing in neuronal and non-neuronal systems. Taken together, our results demonstrate for the first time that Katanin 60 is required for the normal development of neuromuscular synapses and dendrites.

Katanin p80 Regulates Human Cortical Development by Limiting Centriole and Cilia Number

“…In our cohort of microcephalic and lissencephalic pedigrees, we have not yet identified any individuals with KATNA1 mutations. Complete loss of KATNA1 function may be incompatible with embryonic survival, as is the case with Drosophila katanin p60 (Mao et al, 2014), or mutations in KATNA1 may cause an entirely different human phenotype. Further characterization and sequencing in individuals will be necessary to more fully explore the human genetics of katanin mutations.…”

Building the Neuronal Microtubule Cytoskeleton

“…MT severing by katanin and spastin is particularly important for the formation of axonal branches and dendritic development (Yu et al, 2008). Several studies have also uncovered an important role for MT severing in the outgrowth of motor neurons, the formation of NMJs, and axon regeneration (Mao et al, 2014;Stone et al, 2012). Consistent with the axonal defects in various model systems, spastin mutations have been directly linked to axonal pathologies in the human neurodegenerative disease called hereditary spastic paraplegia (HSP) (Fink, 2013).…”

Microtubule nucleation and organization in dendrites

“…37,38 Evidence that microtubule fragment-based nucleation occurs in dendrites comes from the genetic disruption of severing enzymes Spastin, Katanin 60 and Katanin p60-like1, all of which are required for correct dendrite patterning. [39][40][41][42] Moreover, loss of Katanin p60-like1 reduces the frequency of microtubule polymerization events in the terminal branches of class IV neurons. 39 The activity of microtubule-severing enzymes is not restricted to dendrites; they are also required for axonal growth.…”

“…39 The activity of microtubule-severing enzymes is not restricted to dendrites; they are also required for axonal growth. 40,42,43 Spatial regulation of microtubule-severing enzyme activity in neurons is controlled by mechanisms such as the binding of the microtubule-associated protein Tau to microtubules in hippocampal neuron axons 44 and the post-translational modification of dendrite microtubules (polyglutamylation). 45 g-tubulin and microtubule-severing pathways interact in nonneuronal cells, for example to organize meiotic spindle microtubules in C. elegans.…”