Spatial Learning and Motor Deficits in Vacuolar Protein Sorting-associated Protein 13b (Vps13b) Mutant Mouse

Vacuolar protein sorting-associated protein 13B (VPS13B), also known as COH1, is one of the VPS13 family members which is involved in transmembrane transport, Golgi integrity, and neuritogenesis. Mutations in the VPS13B gene are associated with Cohen syndrome and other cognitive disorders such as intellectual disabilities and autism spectrum disorder (ASD). However, the patho-physiology of VPS13B-associated cognitive deficits is unclear, in part, due to the lack of animal models. Here, we generated a Vps13b exon 2 deletion mutant mouse and analyzed the behavioral phenotypes. We found that Vps13b mutant mice showed reduced activity in open field test and significantly shorter latency to fall in the rotarod test, suggesting that the mutants have motor deficits. In addition, we found that Vps13b mutant mice showed deficits in spatial learning in the hidden platform version of the Morris water maze. The Vps13b mutant mice were normal in other behaviors such as anxiety-like behaviors, working memory and social behaviors. Our results suggest that Vps13b mutant mice may recapitulate key clinical symptoms in Cohen syndrome such as intellectual disability and hypotonia. Vps13b mutant mice may serve as a useful model to investigate the pathophysiology of VPS13B-associated disorders.

Specific Expression of Aplysia Phosphodiesterase 4 in Bag Cells Revealed by in situ Hybridization Analysis

Phosphodiesterases (PDEs) play a key role in the regulation of cyclic adenosine monophosphate (cAMP), which in turn mediates various cellular functions including learning and memory. We previously cloned and characterized three PDE4 isoforms (ApPDE4) from Aplysia kurodai. Using reverse transcription polymerase chain reaction (RT-PCR), we found that ApPDE4 isoforms are primarily expressed in the central nervous system. However, the detailed distribution of ApPDE4 mRNA in Aplysia individual ganglions was not evident. In this study, to determine the distribution of ApPDE4 mRNAs in Aplysia ganglions, we performed in situ hybridization (ISH) using a probe targeting ApPDE4, including the PDE catalytic domain. Interestingly, we found the strongest ISH-positive signals in the symmetrical bag cell clusters of the abdominal ganglion. The R2, R14, L7, L2 and L11 neurons in the abdominal ganglion, LP1 neuron in pleural ganglion, and metacerebral (MCC) neurons were ISH-positive. Mechanosensory neurons of the sensory cluster were also stained on the ventral aspect of the right and left pleural ganglia. Taken together, we found the detailed distribution of ApPDE4 mRNA in Aplysia ganglion and support their roles in serotonin (5-HT)-induced synaptic facilitation of Aplysia mechanosensory neurons.

Development of a Touch-Screen-Based Paradigm for Assessing Working Memory in the Mouse

Assessing the working memory of the rodent by using a touch-screen system has several advantages (e.g., allowing highly accurate data collection and flexibility in memory task design). However, there is currently no available testing paradigm utilizing touch-screen systems that can assess working memory in the mouse. In this study, we developed a touch-screen testing paradigm in which mice were trained to choose a location that is matched to a sample location after a time delay. Consistent with previous studies, this study showed that mice could not only learn the rule in the delayed matched to position (DMTP), but also could retain a transitory memory of the sample position during delay. This indicates that a touch-screen system can provide a DMTP testing platform to assess working memory in the mouse.