Improvement of high-resolution chromosome banding methods, and its application to human gene mapping.

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1. Various established methods for high-resolution chromosome banding were re-evaluated and in part improved for their application to different cell culture systems.(1) The ethidium bromide (EB) method was found to be applicable, by improving the dose and duration of treatment with EB and Colcemid, to the well-grown tumor cells in culture.(2) The method of cell synchronization with methotrexate (MTX) and subsequent BrdU treatment which was applied to lymphocyte cultures from the dog (Canis familiaris) yielded sufficient results for high-resolution replication R-banding.(3) A reliable method to obtain high-resolution R-banded chromosomes from lymphoblastoid cell lines (LCL) was established by combination of EB addition (1-1.5 hr) and excess thymidine-induced cell synchronization followed by the BrdU treatment (6.5-7 hrs).2. By applying the EB method to peripheral lymphocyte cultures, the break points of various structural chromosome abnormalities were precisely defined, leading to the regional mapping of the following disease loci : Down syndrome-related region 21q22.2->qter), HMC syndrome (1q31.2 or 7p15.1-p15.3), neurofibromatosis type 2 (22q12.2).3. Fluorescent in situ hybridization was performed for molecular cytogenetic characterization of some structural chromosome abnormalities (rings, pseudodicentrics, etc.) by using DNA probes of repeated sequences (telomere'DNA, rDNA alpha satellite DNA and DNA segments containing Alu repeats). Furthermore, precise regional mapping of a total of 20 DNA segments derived from human No.21 chromosomes were performed by FISH analysis and high-resolution R-banding. They include 13 NotI- and 7 SfiI-linking clones.