Kctd7 deficiency induces myoclonic seizures associated with Purkinje cell death and microvascular defects

Mutations in the potassium channel tetramerization domain-containing 7 (KCTD7) gene are associated with a severe neurodegenerative phenotype characterized by childhood onset of progressive and intractable myoclonic seizures accompanied by developmental regression. KCTD7-driven disease is part of a large family of progressive myoclonic epilepsy syndromes displaying a broad spectrum of clinical severity. Animal models of KCTD7-related disease are lacking, and little is known regarding how KCTD7 protein defects lead to epilepsy and cognitive dysfunction. We characterized Kctd7 expression patterns in the mouse brain during development and show that it is selectively enriched in specific regions as the brain matures. We further demonstrate that Kctd7-deficient mice develop seizures and locomotor defects with features similar to those observed in human KCTD7-associated diseases. We also show that Kctd7 is required for Purkinje cell survival in the cerebellum and that selective degeneration of these neurons is accompanied by defects in cerebellar microvascular organization and patterning. Taken together, these results define a new model for KCTD7-associated epilepsy and identify Kctd7 as a modulator of neuron survival and excitability linked to microvascular alterations in vulnerable regions.

Brain-specific knockin of the pathogenic Tubb5 E401K allele causes defects in motor coordination and prepulse inhibition

The generation, migration, and differentiation of neurons requires the functional integrity of the microtubule cytoskeleton. Mutations in the tubulin gene family are known to cause various neurological diseases including lissencephaly, ocular motor disorders, polymicrogyria and amyotrophic lateral sclerosis. We have previously reported that mutations in TUBB5 cause microcephaly that is accompanied by severe intellectual impairment and motor delay. Here we present the characterization of a Tubb5 mouse model that allows for the conditional expression of the pathogenic E401K mutation. Homozygous knockin animals exhibit a severe reduction in brain size and in body weight. These animals do not show any significant impairment in general activity, anxiety, or in the acoustic startle response, however, present with notable defects in motor coordination. When assessed on the static rod apparatus mice took longer to orient and often lost their balance completely. Interestingly, mutant animals also showed defects in prepulse inhibition, a phenotype associated with sensorimotor gating and considered an endophenotype for schizophrenia. This study provides insight into the behavioral consequences of tubulin gene mutations.

Paraquat exposure induces behavioral deficits in larval zebrafish during the window of dopamine neurogenesis

Exposure to environmental risk factors such as herbicides in early life has been proposed to play important roles in the development of neurodegenerative disorders in adult life. To test this hypothesis, we used a zebrafish model to link the herbicide paraquat (PQ) to disease etiology. Strikingly, treatment of 18 hpf embryonic zebrafish with low-dose PQ treatment (0.04 ppm, lower than the accepted human daily exposure) resulted in 50% display of neurodegenerative phenotypes and motor deficits at various developmental stages (segmentation to larval stage). Wide arrays of biomarkers have been employed to delineate the toxic responses which include lipid peroxidation, glutathione (GSH) and apoptosis studies. A decrease in the GSH levels, increase in lipid peroxidation and apoptosis, respectively, were observed at various developmental stages. Unexpectedly, we show that the exposure to paraquat during the window of dopamine neurogenesis causes Parkinsonian like motor defects in later life by perturbing cholinergic system due to oxidative stress.