High resolution alignment of the physical and genetic maps of the dpy-14 region of chromosome I in Caenorhabditis elegans

The dpy-14 region of chromosome I in the nematode Caenorhabditis elegans has been well characterized both physically and genetically. Lethal alleles of 15 essential genes, including dpy-14(e188ts), have been mapped near to or within the interval defined by unc-87 and the transposon insertion site dimorphism sPl. Much is known about the physical organization of this region, but the number and position of genetic loci have not been determined. The intent of this study was to refine a system for serial cosmid rescue of lethal mutations in the chromosome I gene cluster, starting with essential genes within or near the0.05 map unit unc-87-sP1 interval. Germ line transformation with cosmid clones containing C. elegans genomic DNA was used to generate stable transformants that carried heritable extrachromosomal arrays composed of exogenous DNA. The usefulness of these arrays as genetic mapping tools was explored in this study. Germ line stability of heritable arrays was examined. The arrays were found to be lost from oocytes four- to seven-fold more frequently than in hermaphroditic sperm. However, the arrays were transmitted frequently enough to make it possible to cross them into different genetic backgrounds. Males heterozygous for lethal alleles were mated with hermaphrodites that carried heritable extrachromosomal arrays to perform complementation analysis. A total of 14 genes, including dpy-14, were tested individually against a set of five overlapping cosmid clones that span the entire interval and contain approximately 90 kilobase pairs (kb) of DNA. Five of these genes were positioned by complementation with cosmid clones, producing an alignment between the genetic and physical maps with a resolution of approximately one gene per 18 kb of DNA or 100 genes per map unit. Listed in left to right order, let-398, let-394, let-534, dpy-14 and let-545, were assigned to cosmid clones.Medicine, Faculty ofMedical Genetics, Department ofGraduat