Roles of motor proteins in cerebellar Purkinje neuron biology

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Myosin 10 function in cerebellar Purkinje neurons The Purkinje neuron (PN) is the master neuron of the cerebellum, as it receives all inputs into the cerebellar cortex, is the sole output from the cortex, and is essential for coordination, balance and learning precise motor tasks. We showed previously that myosin Va transports tubules of ER into PN spines to promote synaptic plasticity and motor learning (Wagner et al, Nat. Cell Biol. 2011), and that myosin 18A targets the guanine nucleotide exchange factor -Pix to PN spines to promote spine maturation (Alexander et al, FASEB J 2021). Here we describe ongoing efforts using to define the function of myosin 10 (Myo10) in PNs, which are unique among CNS neurons in possessing very high levels of this filopodial myosin, and in undergoing filopodia-to-spine conversion without prior innervation. At the whole organ level, six week-old Myo10 knockout (KO) mice (Heimsath et al, Sci. Rep. 2017) exhibit cerebellar hypoplasia and misshapen and/or missing cerebellar lobes. Additionally, Calbindin staining of cerebellar slices from these mice reveals defects in the alignment of PN soma and in the orientation of PN dendritic arbors within the molecule layer. Importantly, Calbindin staining of cerebellar slices from mature, six month-old Myo10 KO mice reveals major defects in PN morphology, including reduced dendritic arborization and greatly reduced spine density. Consistent with these observations, Myo10 KO mice exhibit significant defects in cerebellar function (e.g. maintaining balance). Finally, GFP-tagged Myo10 expressed in cultured PNs localizes dramatically at the tips of filopodia-like extensions at the leading edge of forming neurites, and the miRNA-mediated knockdown of Myo10 in these cells results in defects in spine maturation and cell polarity (reduced dendritic arborization, increased number of axons). Together, these results argue that Myo10 is required for normal cerebellar development, cerebellar function, and PN structure and function, and they pave the way for future efforts designed to identify the molecular mechanisms by which this MyTH4/FERM myosin promotes these processes.