It is evident that in the present study several points remained to be clarified

Postmitotic Butein supplier neurons express also cell cycle proteins, which are involved in neuronal morphogenesis and in the regulation of pre-synaptic differentiation, such as CDC20 through interaction with a multiprotein anaphase-promoting complex. Upregulation of PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19636622 cell cycle genes in Cstb2/2 granule neurons may also imply to functions of CSTB in the nucleus. CSTB localizes to the cytoplasm, where it associates with lysosomes, but it has also been detected in the nucleus of dividing cells. In the nucleus, CSTB has been shown to interact with histones and cathepsin L and to regulate cell cycle progression into the S phase. It is tempting to speculate that the synaptic changes may, at least partly, be mediated by cathepsins in the cells, including the synaptic sites and the nucleus. Imbalance of cathepsin regulation in the synapses could lead to morphological and functional changes. On the other hand, disturbed nuclear function of CSTB, which is at least partially mediated by cathepsin regulation, could result in consequent alterations in the transcriptional regulation of synaptic proteins. Synaptic functions are highly dependent on functional cytoskeleton that regulates intracellular transport and protein turnover in the synapses. Cstb2/2 granule neurons revealed also significant overexpression of several genes encoding kinesins, CCN family of proteins and annexins, that have been associated in axonal transport, nuclear division, mitosis, extracellular matrix production, apoptosis and GABAergic signaling. Taken together, the data from Cstb2/2 granule cells propose neuron specific alterations in processes central to neuronal function and architecture and emphasizes nuclear functions of CSTB. As the gene expression data from P7 Cstb2/2 cerebellum and neurons alluded to alterations in synaptic functions, which could contribute to the neuronal hyperexcitability and characteristic motor symptoms seen in EPM1 patients, we selected GABAergic signaling for more detailed characterization. At P7, mRNA levels of granule cell specific GABAA receptor subtypes a6 and d were elevated, although not highly enough to be able to detect at protein level. However, electrophysiological analyses of Cstb2/2 mouse cerebellar slices showed a shift of balance towards Gene Expression Alterations in Cstb2/2 Mouse decreased inhibition and increased excitation in the Purkinje cells. Thus, the detected upregulation of GABAA receptor subunit mRNAs at P7 Cstb2/2 mouse could reflect a compensatory change in gene expression to decrease the excitatory PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19639073 neurotransmission from granule cells to Purkinje cells, especially as the GABAA receptor subunit mRNAs, which were upregulated, were those for the a6 and d subunits that mostly form extrasynaptic receptors responsible for tonic inhibition. On the other hand, at P30, we found reduced ligand binding to a6 and d subunit-containing GABAA receptors indicating alterations in functional postsynaptic and extrasynaptic receptors in Cstb2/2 mouse cerebellum at this age. Whether the changes in GABAA receptor function could be due to e.g. availability of different receptor subtypes in the membrane needs to be investigated. A decrease in the number of GABAergic terminals leading to reduced GABA inhibition has previously been reported in cerebral cortex of aged Cstb2/2 mice. The loss of interneurons in aged mice can further reduce the GABA inhibition. Consistent with the mouse data, a loss of pre-synaptic GABAergic marker VGAT was also detected in the br