Mapping ESTs by fiber-FISH

A visual transcript map of six genes was constructed on the chromosome 21q2 2.3 by high resolution fluorescence in situ hybridization (FISH). Expressed sequence tag (ESTs) from six genes-PWP2, KNP1, AIRE, C21orf3, SMT3A and C2 1orf1-were successfully localized by fiber-FISH by use of sensitive tyramid e-based detection. The sizes of the ESTs varied between 315 to 956 bp and m ost of them map within the 3'-untranslated region. The ESTs were assigned t o and subsequently ordered within cosmid, PAC,and BAC clones hybridized on DNA Fibers. Physical distances between ESTs and known markers were determin ed. Our results demonstrate the Feasibility and accuracy of visual mapping EST sequences in relation to known markers. The main advantage of this appr oach is that it can be applied to finely map any of the database ESTs for p ositional cloning efforts. The sensitivity, specificity, and reproducibilit y of this high-resolution EST mapping technique is evaluated.