This work was supported by grants AG030709 from NIH/NIA and 07-65798 from the California Department of Public Health. We acknowledge Margaret M. Condron for peptide synthesis and amino acid analysis, Dr. Elizabeth F. Neufeld for helping and supporting the initial steps of the project, Dr. Chi-Hong B. Chen for providing support and reagents, and Dr. Andrew D. Ellington for helpful discussions.

<ol>
	<li>Monien, B. H., Apostolova, L. G., Bitan, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Early+diagnostics+and+therapeutics+for+Alzheimer's+disease-how+early+can+we+get+there.">Early diagnostics and therapeutics for Alzheimer's disease-how early can we get there.</a> Expert. Rev. Neurother. 6, 1293-1306 (2006).</li><li>Nestor, P. J., Scheltens, P., Hodges, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Advances+in+the+early+detection+of+Alzheimer's+disease.">Advances in the early detection of Alzheimer's disease.</a> Nat. Med. 10, S34-S41 (2004).</li><li>Kawas, C. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clinical+practice.+Early+Alzheimer's+disease.">Clinical practice. Early Alzheimer's disease.</a> N. Engl. J. Med. 349, 1056-1063 (2003).</li><li>Haass, C., Selkoe, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Soluble+protein+oligomers+in+neurodegeneration:+lessons+from+the+Alzheimer's+amyloid+&#946;-peptide.">Soluble protein oligomers in neurodegeneration: lessons from the Alzheimer's amyloid &#946;-peptide.</a> Nat. Rev. Mol. Cell. Biol. 8, 101-112 (2007).</li><li>Kirkitadze, M. D., Bitan, G., Teplow, D. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Paradigm+shifts+in+Alzheimer's+disease+and+other+neurodegenerative+disorders:+the+emerging+role+of+oligomeric+assemblies.">Paradigm shifts in Alzheimer's disease and other neurodegenerative disorders: the emerging role of oligomeric assemblies.</a> J. Neurosci. Res. 69, 567-577 (2002).</li><li>Rahimi, F., Shanmugam, A., Bitan, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure-function+relationships+of+pre-fibrillar+protein+assemblies+in+Alzheimer's+disease+and+related+disorders.">Structure-function relationships of pre-fibrillar protein assemblies in Alzheimer's disease and related disorders.</a> Curr. Alzheimer Res. 5, 319-341 (2008).</li><li>Jayasena, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aptamers:+an+emerging+class+of+molecules+that+rival+antibodies+in+diagnostics.">Aptamers: an emerging class of molecules that rival antibodies in diagnostics.</a> Clin. Chem. 45, 1628-1650 (1999).</li><li>Bunka, D. H., Stockley, P. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aptamers+come+of+age+-+at+last.">Aptamers come of age - at last.</a> Nat. Rev. Microbiol. 4, 588-596 (2006).</li><li>Ellington, A. D., Szostak, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+selection+of+RNA+molecules+that+bind+specific+ligands.">In vitro selection of RNA molecules that bind specific ligands.</a> Nature. 346, 818-822 (1990).</li><li>Tuerk, C., Gold, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Systematic+evolution+of+ligands+by+exponential+enrichment:+RNA+ligands+to+bacteriophage+T4+DNA+polymerase.">Systematic evolution of ligands by exponential enrichment: RNA ligands to bacteriophage T4 DNA polymerase.</a> Science. 249, 505-510 (1990).</li><li>Lee, J. F., Stovall, G. M., Ellington, A. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aptamer+therapeutics+advance.">Aptamer therapeutics advance.</a> Curr. Opin. Chem. Biol. 10, 282-289 (2006).</li><li>Weiss, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RNA+aptamers+specifically+interact+with+the+prion+protein+PrP.">RNA aptamers specifically interact with the prion protein PrP.</a> J. Virol. 71, 8790-8797 (1997).</li><li>Bibby, D. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Application+of+a+novel+in+vitro+selection+technique+to+isolate+and+characterise+high+affinity+DNA+aptamers+binding+mammalian+prion+proteins.">Application of a novel in vitro selection technique to isolate and characterise high affinity DNA aptamers binding mammalian prion proteins.</a> J. Virol. Methods. 151, 107-115 (2008).</li><li>Rhie, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+2'-fluoro-RNA+aptamers+that+bind+preferentially+to+disease-associated+conformations+of+prion+protein+and+inhibit+conversion.">Characterization of 2'-fluoro-RNA aptamers that bind preferentially to disease-associated conformations of prion protein and inhibit conversion.</a> J. Biol. Chem. 278, 39697-39705 (2003).</li><li>King, D. J., Safar, J. G., Legname, G., Prusiner, S. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thioaptamer+interactions+with+prion+proteins:+sequence-specific+and+non-specific+binding+sites.">Thioaptamer interactions with prion proteins: sequence-specific and non-specific binding sites.</a> J. Mol. Biol. 369, 1001-1014 (2007).</li><li>Proske, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prion-protein-specific+aptamer+reduces+PrPSc+formation.">Prion-protein-specific aptamer reduces PrPSc formation.</a> ChemBioChem. 3, 717-725 (2002).</li><li>Murakami, K., Nishikawa, F., Noda, K., Yokoyama, T., Nishikawa, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anti-bovine+prion+protein+RNA+aptamer+containing+tandem+GGA+repeat+interacts+both+with+recombinant+bovine+prion+protein+and+its+&#946;+isoform+with+high+affinity.">Anti-bovine prion protein RNA aptamer containing tandem GGA repeat interacts both with recombinant bovine prion protein and its &#946; isoform with high affinity.</a> Prion. 2, 73-80 (2008).</li><li>Luhrs, T., Zahn, R., Wuthrich, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amyloid+formation+by+recombinant+full-length+prion+proteins+in+phospholipid+bicelle+solutions.">Amyloid formation by recombinant full-length prion proteins in phospholipid bicelle solutions.</a> J. Mol. Biol. 357, 833-841 (2006).</li><li>Bunka, D. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Production+and+characterization+of+RNA+aptamers+specific+for+amyloid+fibril+epitopes.">Production and characterization of RNA aptamers specific for amyloid fibril epitopes.</a> J. Biol. Chem. 282, 34500-34509 (2007).</li><li>Ylera, F., Lurz, R., Erdmann, V. A., Furste, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Selection+of+RNA+aptamers+to+the+Alzheimer's+disease+amyloid+peptide.">Selection of RNA aptamers to the Alzheimer's disease amyloid peptide.</a> Biochem. Biophys. Res. Commun. 290, 1583-1588 (2002).</li><li>Rahimi, F., Murakami, K., Summers, J. L., Chen, C. H., Bitan, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RNA+aptamers+generated+against+oligomeric+A&#946;40+recognize+common+amyloid+aptatopes+with+low+specificity+but+high+sensitivity.">RNA aptamers generated against oligomeric A&#946;40 recognize common amyloid aptatopes with low specificity but high sensitivity.</a> PLoS ONE. 4, e7694-e7694 (2009).</li><li>Bitan, G., Lomakin, A., Teplow, D. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amyloid+&#946;-protein+oligomerization:+prenucleation+interactions+revealed+by+photo-induced+cross-linking+of+unmodified+proteins.">Amyloid &#946;-protein oligomerization: prenucleation interactions revealed by photo-induced cross-linking of unmodified proteins.</a> J. Biol. Chem. 276, 35176-35184 (2001).</li><li>Rahimi, F., Maiti, P., Bitan, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photo-induced+cross-linking+of+unmodified+proteins+(PICUP)+applied+to+amyloidogenic+peptides.">Photo-induced cross-linking of unmodified proteins (PICUP) applied to amyloidogenic peptides.</a> J. Vis. Exp. , (2009).</li><li>Bitan, G., Fradinger, E. A., Spring, S. M., Teplow, D. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neurotoxic+protein+oligomers-what+you+see+is+not+always+what+you+get.">Neurotoxic protein oligomers-what you see is not always what you get.</a> Amyloid. 12, 88-95 (2005).</li><li>Bitan, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structural+study+of+metastable+amyloidogenic+protein+oligomers+by+photo-induced+cross-linking+of+unmodified+proteins.">Structural study of metastable amyloidogenic protein oligomers by photo-induced cross-linking of unmodified proteins.</a> Methods Enzymol. 413, 217-236 (2006).</li><li>Chen, C. H., Chernis, G. A., Hoang, V. Q., Landgraf, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inhibition+of+heregulin+signaling+by+an+aptamer+that+preferentially+binds+to+the+oligomeric+form+of+human+epidermal+growth+factor+receptor-3.">Inhibition of heregulin signaling by an aptamer that preferentially binds to the oligomeric form of human epidermal growth factor receptor-3.</a> Proc. Natl. Acad. Sci. USA. 100, 9226-9231 (2003).</li><li>Adams, D. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Lab math: a handbook of measurements, calculations, and other quantitative skills for use at the bench. , (2003).</li><li>Gopinath, S. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methods+developed+for+SELEX.">Methods developed for SELEX.</a> Anal. Bioanal. Chem. 387, 171-182 (2007).</li><li>Takahashi, T., Tada, K., Mihara, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RNA+aptamers+selected+against+amyloid+&#946;-peptide+(A&#946;)+inhibit+the+aggregation+of+A&#946;.">RNA aptamers selected against amyloid &#946;-peptide (A&#946;) inhibit the aggregation of A&#946;.</a> Mol. Biosyst. 5, 986-991 (2009).</li></ol>

No conflicts of interest declared.

The starting point of the SELEX process is synthesis of a random oligonucleotide library typically containing 1012-1015 sequences. In DNA SELEX, this library is used directly after a ssDNA pool is generated, whereas in RNA SELEX, demonstrated here, the ssDNA library is converted first to an RNA pool enzymatically by in-vitro transcription. Then, SELEX is performed iteratively whereby each cycle comprises exposure and binding of oligonucleotides to the intended target, partitioning of binder...

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		<table border="1">
		<thead>
		<tr>
		<th>Material Name</th>
		<th>Type</th>
		<th>Company</th>
		<th>Catalogue Number</th>
		<th>Comment</th>
		</tr>
		</thead>
		<tbody>
		
<tr>
<td>A&beta;40</td>
<td>&nbsp;</td>
<td>UCLA Biopolymers Laboratory</td>
<td>&nbsp;</td>
<td>Lyophilized powder</td>
</tr>
<tr>
<td>MX5 Automated-S Microbalance</td>
<td>&nbsp;</td>
<td>Mettler Toledo</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Silicon-coated, 1.6-ml tubes</td>
<td>&nbsp;</td>
<td>Denville Scientific</td>
<td>C19033 or C19035</td>
<td>&nbsp;</td>
<tr>
<td>1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)</td>
<td>&nbsp;</td>
<td>TCI America</td>
<td>H0424</td>
<td>Use in a fume hood.</td>
</tr>
<tr>
<td>Ammonium persulfate</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>A-7460</td>
<td>Vortex until the solution is clear. APS is prepared freshly each time and should be used within 48 h.</td>
</tr>
<tr>
<td>Tris(2,2-bipridyl)dichlororuthenium(II) hexahydrate</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>224758-1G</td>
<td>Vortex until the solution is clear. Cover the RuBpy tube with foil to protect the reagent from ambient light. RuBpy is prepared freshly each time and should be used within 48 h.</td>
</tr>
<tr>
<td>Dithiothreitol (DTT)</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>43815</td>
<td>&nbsp;</td>
<tr>
<td>D-Salt&trade; Excellulose&trade; desalting columns</td>
<td>&nbsp;</td>
<td>Thermo Scientific</td>
<td>20449</td>
<td>&nbsp;</td>
<tr>
<td>Ammonium acetate	</td>
<td>&nbsp;</td>
<td>Fisher Scientific</td>
<td>A637-500</td>
<td>&nbsp;</td>
<tr>
<td>Silicon-coated, 0.6-ml tubes</td>
<td>&nbsp;</td>
<td>Denville Scientific</td>
<td>C19063</td>
<td>&nbsp;</td>
<tr>
<td>Novex Tricine Gels (10&#x2013;20%)</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>EC6625B0X</td>
<td>10-well; mini size (8 cm X 8 cm); 25 &mu;l loading volume per well; separation range 5 kDa to 40 kDa</td>
</tr>
<tr>
<td>Quartz cuvette</td>
<td>&nbsp;</td>
<td>Hellma</td>
<td>105.250-QS</td>
<td>&nbsp;</td>
<tr>
<td>Beckman DU 640 spectrophotometer</td>
<td>&nbsp;</td>
<td>Beckman</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>ssDNA library</td>
<td>&nbsp;</td>
<td>Integrated DNA Technologies</td>
<td>Custom-ordered</td>
<td>The library was designed to contain 49 random nucleotides flanked by two constant regions containing primer-binding and cloning sites: 
5'-TAA TAC GAC TCA CTA TAG GGA ATT CCG CGT GTG C (N:25:25:25:25%) (N)49 G TCC GTT CGG GAT CCT C-3'</td>
</tr>
<tr>
<td>Taq DNA polymerase</td>
<td>&nbsp;</td>
<td>USB Corporation</td>
<td>71160</td>
<td>Recombinant Thermus aquaticus DNA Polymerase supplied with 10&#215; PCR Buffer and a separate tube of 25 mM MgCl2 for routine PCR.</td>
</tr>
<tr>
<td>PCR Nucleotide Mix, 10 mM solution</td>
<td>&nbsp;</td>
<td>USB Corporation</td>
<td>77212</td>
<td>(10 mM each dATP, dCTP, dGTP, dTTP)</td>
</tr>
<tr>
<td>Forward primer</td>
<td>&nbsp;</td>
<td>Integrated DNA Technologies</td>
<td>Custom-ordered</td>
<td>5'-TAA TAC GAC TCA CTA TAG GGA ATT CCG CGT GTG C-3'</td>
</tr>
<tr>
<td>Reverse primer</td>
<td>&nbsp;</td>
<td>Integrated DNA Technologies</td>
<td>Custom-ordered</td>
<td>5'-GAG GAT CCC GAA CGG AC-3'</td>
</tr>
<tr>
<td>Thermal cycler</td>
<td>&nbsp;</td>
<td>Denville Scientific</td>
<td>Techne TC-312</td>
<td>&nbsp;</td>
<tr>
<td>QIAquick PCR Purification Kit (50)</td>
<td>&nbsp;</td>
<td>QIAGEN</td>
<td>28104</td>
<td>&nbsp;</td>
<tr>
<td>Agarose</td>
<td>&nbsp;</td>
<td>Denville Scientific</td>
<td>CA3510-8</td>
<td>&nbsp;</td>
<tr>
<td>Conical, sterile 1.6-ml tubes with caps attached with O-rings</td>
<td>&nbsp;</td>
<td>Denville Scientific</td>
<td>C19040-S</td>
<td>&nbsp;</td>
<tr>
<td>RiboMAX&trade; Large Scale RNA Production System&#x2013;T7</td>
<td>&nbsp;</td>
<td>Promega</td>
<td>P1300</td>
<td>The kit contains: 120 &mu;l Enzyme Mix (RNA polymerase, recombinant RNasin&reg; ribonuclease inhibitor and recombinant inorganic pyrophosphatase); 240 &mu;l transcription 5 buffer; 100 &mu;l each of 4 rNTPs, 100 mM; 110 U RQ1 RNase-free DNase, 1 U/&mu;l; 10 &mu;l linear control DNA, 1 mg/ml; 1 ml 3M sodium acetate (pH 5.2); 1.25 ml nuclease-Free water</td>
</tr>
<tr>
<td>&alpha;-32P-cytidine 5'-triphosphate, 250 &mu;Ci (9.25 MBq), </td>
<td>&nbsp;</td>
<td>Perkin Elmer</td>
<td>BLU008H250UC</td>
<td>Specific Activity: 3000 Ci (111 TBq)/mmol, 50 mM Tricine (pH 7.6)</td>
</tr>
<tr>
<td>Citrate-saturated phenol:chloroform:isoamyl alcohol (125:24:1, pH 4.7)</td>
<td>&nbsp;</td>
<td>Sigma (Fluka)</td>
<td>77619</td>
<td>&nbsp;</td>
<tr>
<td>Chloroform:Isoamyl alcohol (24:1)</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>C0549</td>
<td>&nbsp;</td>
<tr>
<td>Absolute ethanol for molecular biology</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>E7023</td>
<td>&nbsp;</td>
<tr>
<td>Z216-MK refrigerated microcentrifuge</td>
<td>&nbsp;</td>
<td>Denville Scientific</td>
<td>C0216-MK</td>
<td>&nbsp;</td>
<tr>
<td>illustra ProbeQuant&trade; G-50 Micro Columns</td>
<td>&nbsp;</td>
<td>GE Healthcare</td>
<td>Obtained from Fisher Scientific (45-001-487)</td>
<td>Prepacked with Sephadex&trade; G-50 DNA Grade and pre-equilibrated in STE buffer containing 0.15% Kathon as Biocide</td>
</tr>
<tr>
<td>Triathler Bench-top Scintillation counter</td>
<td>&nbsp;</td>
<td>Hidex Oy, Turku, Finland</td>
<td>Triathler LSC Model: 425-034</td>
<td>&nbsp;</td>
<tr>
<td>Novex&reg; TBE-Urea Sample Buffer (2&#215;)</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>LC6876</td>
<td>&nbsp;</td>
<tr>
<td>6% TBE-Urea Gels 1.0 mm, 10 wells</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>EC6865BOX</td>
<td>&nbsp;</td>
<tr>
<td>Novex&reg; TBE Running Buffer (5&#215;)</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>LC6675</td>
<td>&nbsp;</td>
<tr>
<td>Radioactivity decontaminant</td>
<td>&nbsp;</td>
<td>Fisher Scientific</td>
<td>04-355-67</td>
<td>&nbsp;</td>
<tr>
<td>Gel-loading tips</td>
<td>&nbsp;</td>
<td>Denville Scientific</td>
<td>P3080</td>
<td>&nbsp;</td>
<tr>
<td>XCell SureLock Mini-Cell</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>EI0001</td>
<td>XCell SureLock Mini-Cell</td>
</tr>
<tr>
<td>Autoradiography film</td>
<td>&nbsp;</td>
<td>Denville Scientific</td>
<td>E3018</td>
<td>Use in complete darkness</td>
</tr>
<tr>
<td>Autoradiography film, Hyperfilm&trade; ECL</td>
<td>&nbsp;</td>
<td>Amersham Biosciences</td>
<td>RPN3114K</td>
<td>Can be used under red safe light.</td>
</tr>
<tr>
<td>Membrane discs</td>
<td>&nbsp;</td>
<td>Millipore</td>
<td>GSWP02500</td>
<td>Mixed cellulose ester, hydrophilic, 0.22-&mu;m disc membranes</td>
</tr>
<tr>
<td>Fritted glass support base for 125-ml flask</td>
<td>&nbsp;</td>
<td>VWR</td>
<td>26316-696</td>
<td>&nbsp;</td>
<tr>
<td>Petri dishes</td>
<td>&nbsp;</td>
<td>Fisher Scientific</td>
<td>08-757-11YZ</td>
<td>&nbsp;</td>
<tr>
<td>Urea	</td>
<td>&nbsp;</td>
<td>Fisher Scientific</td>
<td>AC32738-0050</td>
<td>&nbsp;</td>
<tr>
<td>EDTA</td>
<td>&nbsp;</td>
<td>Fisher Scientific</td>
<td>118430010</td>
<td>&nbsp;</td>
<tr>
<td>Glycogen</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>G1767</td>
<td>&nbsp;</td>
<tr>
<td>2-Propanol for molecular biology</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>I9516</td>
<td>&nbsp;</td>
<tr>
<td>Recombinant RNase inhibitor</td>
<td>&nbsp;</td>
<td>USB Corporation</td>
<td>71571</td>
<td>&nbsp;</td>
<tr>
<td>ImProm-II&trade;Reverse Transcription System</td>
<td>&nbsp;</td>
<td>Promega</td>
<td>A3802</td>
<td>&nbsp;</td>
<tr>
<td>Recombinant RNase inhibitor</td>
<td>&nbsp;</td>
<td>USB Corporation</td>
<td>71571</td>
<td>&nbsp;</td>
<tr>
<td>RapidRun&trade; Loading Dye</td>
<td>&nbsp;</td>
<td>USB Corporation</td>
<td>77524</td>
<td>&nbsp;</td>		</tbody>
		</table>
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selection of aptamers for amyloid &beta;-protein, the causative agent of alzheimer&#39;s disease

Alzheimer's disease (AD) is a progressive, age-dependent, neurodegenerative disorder with an insidious course that renders its presymptomatic diagnosis difficult1. Definite AD diagnosis is achieved only postmortem, thus establishing presymptomatic, early diagnosis of AD is crucial for developing and administering effective therapies2,3.
Amyloid &beta;-protein (A&beta;) is central to AD pathogenesis. Soluble, oligomeric A&beta; assemblies are believed to affect neurotoxicity underlying synaptic dysfunction and neuron loss in AD4,5. Various forms of soluble A&beta; assemblies have been described, however, their interrelationships and relevance to AD etiology and pathogenesis are complex and not well understood6. Specific molecular recognition tools may unravel the relationships amongst A&beta; assemblies and facilitate detection and characterization of these assemblies early in the disease course before symptoms emerge. Molecular recognition commonly relies on antibodies. However, an alternative class of molecular recognition tools, aptamers, offers important advantages relative to antibodies7,8. Aptamers are oligonucleotides generated by in-vitro selection: systematic evolution of ligands by exponential enrichment (SELEX)9,10. SELEX is an iterative process that, similar to Darwinian evolution, allows selection, amplification, enrichment, and perpetuation of a property, e.g., avid, specific, ligand binding (aptamers) or catalytic activity (ribozymes and DNAzymes).
Despite emergence of aptamers as tools in modern biotechnology and medicine11, they have been underutilized in the amyloid field. Few RNA or ssDNA aptamers have been selected against various forms of prion proteins (PrP)12-16. An RNA aptamer generated against recombinant bovine PrP was shown to recognize bovine PrP-&beta;17, a soluble, oligomeric, &beta;-sheet-rich conformational variant of full-length PrP that forms amyloid fibrils18. Aptamers generated using monomeric and several forms of fibrillar &beta;2-microglobulin (&beta;2m) were found to bind fibrils of certain other amyloidogenic proteins besides &beta;2m fibrils19. Ylera et al. described RNA aptamers selected against immobilized monomeric A&beta;4020. Unexpectedly, these aptamers bound fibrillar A&beta;40. Altogether, these data raise several important questions. Why did aptamers selected against monomeric proteins recognize their polymeric forms? Could aptamers against monomeric and/or oligomeric forms of amyloidogenic proteins be obtained? To address these questions, we attempted to select aptamers for covalently-stabilized oligomeric A&beta;4021 generated using photo-induced cross-linking of unmodified proteins (PICUP)22,23. Similar to previous findings17,19,20, these aptamers reacted with fibrils of A&beta; and several other amyloidogenic proteins likely recognizing a potentially common amyloid structural aptatope21. Here, we present the SELEX methodology used in production of these aptamers21.

Watch this Scientific Journal Video about Selection of Aptamers for Amyloid Î²-Protein, the Causative Agent of Alzheimer's Disease at JoVE.com

Selection of Aptamers for Amyloid &amp;#946;-Protein, the Causative Agent of Alzheimer&#039;s Disease

Aptamers are short ribo-/deoxyribo-oligonucleotides selected by in-vitro evolution methods based on affinity for a specific target. Aptamers are molecular recognition tools with versatile therapeutic, diagnostic, and research applications. We demonstrate methods for selection of aptamers for amyloid &beta;-protein, the causative agent of Alzheimer's disease.

Selection of Aptamers for Amyloid &beta;-Protein, the Causative Agent of Alzheimer&#39;s Disease

Alzheimer's disease (AD) is a progressive, age-dependent, neurodegenerative disorder with an insidious course that renders its presymptomatic diagnosis ...

selection-aptamers-for-amyloid-protein-causative-agent-alzheimer-s

Research

JoVE Journal

Neuroscience

19.3K Views.  David Geffen School of Medicine. Aptamers are short ribo-/deoxyribo-oligonucleotides selected by in-vitro evolution methods based on affinity for a specific target. Aptamers are molecular recognition tools with versatile therapeutic, diagnostic, and research applications. We demonstrate methods for selection of aptamers for amyloid β-protein, the causative agent of Alzheimer's disease.