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Here we describe a protocol to generate a co-culture consisting of 2 different neuronal populations. Induced pluripotent stem cells (iPSCs) are reprogrammed from human fibroblasts using episomal vectors. Colonies of iPSCs can be observed 30 days after initiation of fibroblast reprogramming. Pluripotent colonies are manually picked and grown in neural induction medium to permit differentiation into neural progenitor cells (NPCs). iPSCs rapidly convert into neuroepithelial cells within 1 week and retain the capability to self-renew when maintained at a high culture density. Primary mouse NPCs are differentiated into astrocytes by exposure to a serum-containing medium for 7 days and form a monolayer upon which embryonic day 18 (E18) rat cortical neurons (transfected with channelrhodopsin-2 (ChR2)) are added. Human NPCs tagged with the fluorescent protein,tandem dimer Tomato (tdTomato),are then seeded onto the astrocyte/cortical neuron culture the following day and allowed to differentiate for 28 to 35 days. We demonstrate that this system forms synaptic connections between iPSC-derived neurons and cortical neurons,evident from an increase in the frequency of synaptic currents upon photostimulation of the cortical neurons. This co-culture system provides a novel platform for evaluating the ability of iPSC-derived neurons to create synaptic connections with other neuronal populations. View Publication

Serotonergic axons from the raphe nuclei in the brainstem project to every region of the brain,where they make connections through their extensive terminal arborizations. This serotonergic innervation contributes to various normal behaviors and psychiatric disorders. The protocadherin-alpha (Pcdha) family of clustered protocadherins consists of 14 cadherin-related molecules generated from a single gene cluster. We found that the Pcdhas were strongly expressed in the serotonergic neurons. To elucidate their roles,we examined serotonergic fibers in a mouse mutant (Pcdha(Delta CR/Delta CR)) lacking the Pcdha cytoplasmic region-encoding exons,which are common to the gene cluster. In the first week after birth,the distribution pattern of serotonergic fibers in Pcdha(Delta CR/Delta CR) mice was similar to wild-type,but by 3 weeks of age,when the serotonergic axonal termini complete their arborizations,the distribution of the projections was abnormal. In some target regions,notably the globus pallidus and substantia nigra,the normally even distribution of serotonin axonal terminals was,in the mutants,dense at the periphery of each region,but sparse in the center. In the stratum lacunosum-molecular of the hippocampus,the mutants showed denser serotonergic innervation than in wild-type,and in the dentate gyrus of the hippocampus and the caudate-putamen,the innervation was sparser. Together,the abnormalities suggested that Pcdha proteins are important in the late-stage maturation of serotonergic projections. Further examination of alternatively spliced exons encoding the cytoplasmic tail showed that the A-type (but not the B-type) cytoplasmic tail was essential for the normal development of serotonergic projections. View Publication

Certain limitations of the neurosphere assay (NSA) have resulted in a search for alternative culture techniques for brain tumor-initiating cells (TICs). Recently,reports have described growing glioblastoma (GBM) TICs as a monolayer using laminin. We performed a side-by-side analysis of the NSA and laminin (adherent) culture conditions to compare the growth and expansion of GBM TICs. GBM cells were grown using the NSA and adherent culture conditions. Comparisons were made using growth in culture,apoptosis assays,protein expression,limiting dilution clonal frequency assay,genetic affymetrix analysis,and tumorigenicity in vivo. In vitro expansion curves for the NSA and adherent culture conditions were virtually identical (P=0.24) and the clonogenic frequencies (5.2% for NSA vs. 5.0% for laminin,P=0.9) were similar as well. Likewise,markers of differentiation (glial fibrillary acidic protein and beta tubulin III) and proliferation (Ki67 and MCM2) revealed no statistical difference between the sphere and attachment methods. Several different methods were used to determine the numbers of dead or dying cells (trypan blue,DiIC,caspase-3,and annexin V) with none of the assays noting a meaningful variance between the two methods. In addition,genetic expression analysis with microarrays revealed no significant differences between the two groups. Finally,glioma cells derived from both methods of expansion formed large invasive tumors exhibiting GBM features when implanted in immune-compromised animals. A detailed functional,protein and genetic characterization of human GBM cells cultured in serum-free defined conditions demonstrated no statistically meaningful differences when grown using sphere (NSA) or adherent conditions. Hence,both methods are functionally equivalent and remain suitable options for expanding primary high-grade gliomas in tissue culture. View Publication

The prion protein (PrP) is highly conserved and ubiquitously expressed,suggesting that it plays an important physiological function. However,despite decades of investigation,this role remains elusive. Here,by using animal and cellular models,we unveil a key role of PrP in the DNA damage response. Exposure of neurons to a genotoxic stress activates PRNP transcription leading to an increased amount of PrP in the nucleus where it interacts with APE1,the major mammalian endonuclease essential for base excision repair,and stimulates its activity. Preventing the induction of PRNP results in accumulation of abasic sites in DNA and impairs cell survival after genotoxic treatment. Brains from Prnp(-/-) mice display a reduced APE1 activity and a defect in the repair of induced DNA damage in vivo. Thus,PrP is required to maintain genomic stability in response to genotoxic stresses. View Publication

Aberrant neural progenitor cell (NPC) proliferation and self-renewal have been linked to age-related neurodegeneration and neurodegenerative disorders including Alzheimer's disease (AD). Rhizoma Acori tatarinowii is a traditional Chinese herbal medicine against cognitive decline. In this study,we found that the extract of Rhizoma Acori tatarinowii (AT) and its active constituents,asarones,promote NPC proliferation. Oral administration of AT enhanced NPC proliferation and neurogenesis in the hippocampi of adult and aged mice as well as that of transgenic AD model mice. AT and its fractions also enhanced the proliferation of NPCs cultured in vitro. Further analysis identified α-asarone and β-asarone as the two active constituents of AT in promoting neurogenesis. Our mechanistic study revealed that AT and asarones activated extracellular signal-regulated kinase (ERK) but not Akt,two critical kinase cascades for neurogenesis. Consistently,the inhibition of ERK activities effectively blocked the enhancement of NPC proliferation by AT or asarones. Our findings suggest that AT and asarones,which can be orally administrated,could serve as preventive and regenerative therapeutic agents to promote neurogenesis against age-related neurodegeneration and neurodegenerative disorders. View Publication