Loss of Piccolo function in rats induces cerebellar network dysfunction and Pontocerebellar Hypoplasia type 3-like phenotypes

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Item Type:	Article
Title:	Loss of Piccolo function in rats induces cerebellar network dysfunction and Pontocerebellar Hypoplasia type 3-like phenotypes
Creators Name:	Falck, J., Bruns, C., Hoffmann-Conaway, S., Straub, I., Plautz, E.J., Orlando, M., Munawar, H., Rivalan, M., Winter, Y., Izsvák, Z., Schmitz, D., Hamra, F.K., Hallermann, S., Curtis Garner, C. and Ackermann, F.
Abstract:	Piccolo, a presynaptic active zone protein, is best known for its role in the regulated assembly and function of vertebrate synapses. Genetic studies suggest a further link to several psychiatric disorders as well as Pontocerebellar Hypoplasia type 3 (PCH3). We have characterized recently generated Piccolo knockout (Pclo(gt/gt)) rats. Analysis of rats of both sexes revealed a dramatic reduction in brain size compared to wildtype (Pclo(wt/wt)) animals, attributed to a decrease in the size of the cerebral cortical, cerebellar and pontine regions. Analysis of the cerebellum and brainstem revealed a reduced granule cell (GC) layer and a reduction in size of pontine nuclei. Moreover, the maturation of mossy fiber (MF) afferents from pontine neurons and the expression of the α6 GABA(A) receptor subunit at the MF-GC synapse are perturbed, as well as the innervation of Purkinje cells by cerebellar climbing fibers (CFs). Ultrastructural and functional studies revealed a reduced size of MF boutons, with fewer synaptic vesicles and altered synaptic transmission. These data imply that Piccolo is required for the normal development, maturation and function of neuronal networks formed between the brainstem and cerebellum. Consistently, behavioral studies demonstrated that adult Pclo(gt/gt) rats display impaired motor coordination, despite adequate performance in tasks that reflect muscle strength and locomotion. Together these data suggest that loss of Piccolo function in patients with PCH3 could be involved in many of the observed anatomical and behavioral symptoms, and that the further analysis of these animals could provide fundamental mechanistic insights into this devastating disorder. SIGNIFICANCE STATEMENT: Pontocerebellar Hypoplasia type 3 (PCH3) is a devastating developmental disorder associated with severe developmental delay, progressive microcephaly with brachycephaly, optic atrophy, seizures and hypertonia with hyperreflexia. Recent genetic studies have identified non-sense mutations in the coding region of the Piccolo gene, suggesting a functional link between this disorder and the presynaptic active zone. Our analysis of Piccolo knockout rats supports this hypothesis, formally demonstrating that anatomical and behavioral phenotypes seen in patients with PCH3 are also exhibited by these Piccolo deficient animals.
Keywords:	Active Zone, Piccolo, Pontocerebellar Hypoplasia, Presynapse, Animals, Rats
Source:	Journal of Neuroscience
ISSN:	0270-6474
Publisher:	Society for Neuroscience
Volume:	40
Number:	14
Page Range:	2943-2959
Date:	1 April 2020
Official Publication:	https://doi.org/10.1523/JNEUROSCI.2316-19.2020
External Fulltext:	View full text on PubMed Central
PubMed:	View item in PubMed

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