REVERSE TRANSCRIPTION-POLYMERASE CHAIN-REACTION DETECTION OF TRANSCRIBED SEQUENCES ON HUMAN CHROMOSOME-21

Seventy-four pairs of oligonucleotides derived from sequence-tagged si tes (STSs) on the long arm of human chromosome 21, specifically from b ands 21q22.1 to 21q22.3, were used in reverse transcription-polymerase chain reactions (RT-PCR) to detect the presence of expressed sequence s in a fetal brain. These STSs included 69 that had not been related t o transcribed sequences and 5 that had detected two known genes and th ree previously isolated cDNA clones. Of the 69 STSs analyzed in RT-PCR , 25 allowed amplification of specific cDNA fragments. The sizes of am plified cDNA fragments match those amplified from either human genomic DNA or somatic hybrid cells containing human chromosome 21. Of the 11 cDNA analyzed in Northern blot hybridizations, 6 hybridized to specif ic RNA species. The rapid screening for cDNA using previously mapped S TSs has provided insight into the distribution of expressed sequences in this region of chromosome 21. Northern blot analysis of the amplifi ed cDNA fragments has revealed interesting candidate genes in two dise ase loci. The marker D21S267 was previously mapped in the Down syndrom e region of chromosome 21, and the marker D21S113 is closely linked to progressive myoclonus epilepsy. The cDNA fragments amplified using th e primer sequences derived from D21S267 and D21S113 hybridized to 7- a nd 6.5-kb transcripts, respectively, which seem to express predominant ly in brain. (C) 1994 Academic Press, Inc.