Total RNAs from different human tissues were purchased from Clontech. A human BAC clone containing the whole human CD200 gene and a pcDNA3.2 expression vector containing SF2/ASF were obtained from The Center for Applied Genomics (Hospital for Sick Children, Toronto). Taq DNA polymerase, T4 DNA ligase and all restriction endonucleases were purchased from New England Biolabs. Random Primers, Superscript Reverse Transcriptase II, Elongase Enzyme, pcDNA3.0 expression vector and all competent cells were purchased from Invitrogen. EndoFree Plasmid purification Maxi Kit and QIAEX II Gel Extraction Kit were ordered from QIAGEN. A purified SF2/ASF recombinant protein was kindly provided by Dr. Blencowe (University of Toronto). Anti-human and mouse SF2/ ASF antibody was obtained from Santa Cruz Biotechnology. Anti-human and mouse b-actin antibody was purchased from BD Biosciences. Small-interfering RNA (siRNA) including SF2/ASF siRNA and a 'scrambled' siRNA were synthesized by Eurogentec. RNA oligonucleotides were synthesized by DNA and RNA Synthesis Center at Hospital for Sick Children (Toronto). All the primers used for polymerase chain reactions (PCRs), real-time PCRs and mutations were synthesized by Invitrogen.