Positional cloning of mouse morphological mutants

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A mouse mutation Tail-short (Ts) exhibits shortened kinky tail and numerous skeletal abnormalities including homeotic anteroposterior patterning problem along the axial skeleton. Ts gene was mapped to the teromeric region of the chromosome 11. To elucidate the function of the Ts gene in mouse embryogenesis, we intended to clone the gene by means of positional cloning. First, we employed a fine mapping of this gene based on a large scale intersubspecific backcross between the mutant stock TsJ/Le-Ts/ + and Japanese wild mouse-derived MSM strains. Ts gene was mapped to a 0.16cM region between two microsatellite markers, D1IMit128 and DlIMit256. We screened mouse YAC and BAC libraries with microsatellite markers tightly linked to the Ts locus and have obtained YAC and BAC clones. Further chromosome walking with the isolated clones allowed us to construct a complete BAC contig covering the Ts causative gene and the critical region of the Ts was narrowed between two new STSs, DI IRin56 and D … More lINigI7. This contig consists of 3 BAC clones, spanning a 250kb DNA fragment. We have isolated several cDNA clones as Ts candidate gene from the critical region by directed cDNA selection using the corresponding BAC. We have obtained several clones derived from mouse embryonic cDNA library. Among these candidate genes, the expression level of Rp138 gene, which encodes one of ribosomal protein subunits, was reduced in Ts mutant mouse. Analysis of the genomic structure of the Ts mutant revealed that it had an 18kb long deletion containing Rpl38. Other two mutations, Rabo torcido (Rbt) and Tail-short shionogi (Tss), were reported to have phenotype similar to Ts and to be mapped to the same region In the chromosome 11. We found that Rbt and Tss have a frame shift mutation and an insertional mutation, respectively. In order to confirm that Rpl38 is the causative gene for Ts, we tried to rescue the Ts mutant lethal phenotype by transgenesis with the wild-type gene of Rpl38. Over expression both of the BAC containing Rpl38 and the Rpl38 cDNA restored the viability of the Ts mutant in a certain genetic background and completely rescued the morphological phenotype. Thus, it appeared that the lethality and the morphological anomalies of Ts mutants, including their homeotic transformation, are caused by the Rpl38 mutation. Less