Physical mapping of mouse collagen genes on chromosome 10 by high-resolution FISH

Fluorescence in situ hybridization (FISH) on mechanically stretched chromosomes (MSCs) and extended DNA fibers enables construction of high-resolution physical maps by accurate ordering and orienting genomic clones as well as by measuring physical lengths of gaps and overlaps between them. These high-resolution FISH targets have hitherto been used mainly in the study of the human genome. Here we have applied both MSCs and extended DNA fibers to the physical mapping of the mouse genome. At first, five mouse collagen genes were localized by metaphase-FISH: Col10a1 to chromosomal bands 10B1-B3; Col13a1 to 10B4; and Col6a1, Col6a2, and Col18a1 to 10B5-C1. The mutual order of the genes, centromere--Col10a1--Col13a1--Col6a2--Col6a1--Col18a1--telomere, was determined by FISH on metaphase chromosomes, MSCs, and extended DNA fibers. To our knowledge, this is the first time mouse metaphase chromosomes have been stretched and used as targets for FISH. We also used MSCs to determine the transcriptional orientations, telomere--5'-->3'--centromere, of both Col13a1 and Col18a1. With fiber-FISH, Col18a1, Col6a1, and Col6a2 were shown to be in a head-to-tail configuration with respective intergenic distances of about 350 kb and 90 kb. Comparison of our physical mapping results with the homologous human data reveals both similarities and differences concerning the chromosomal distribution, order, transcriptional orientations, and intergenic distances of the collagen genes studied.