A transgenic insertional inner ear mutation on mouse chromosome 1

Objectives/Hypothesis: To clone and characterize the integration site of an insertional inner ear mutation, produced in one of fourteen transgenic mou se Lines. The insertion of the transgene led to a mutation in a gene(s) nec essary for normal development of the vestibular labyrinth. Study Design: Mo lecular genetic analysis of a transgene integration site, Methods: Molecula r cloning, Southern and northern blotting, DNA sequencing and genetic datab ase searching were the methods employed. Results: The integration of the tr ansgene resulted in a dominantly inherited waltzing phenotype and in degene ration of the pars superior. During development, inner ear fluid homeostasi s was disrupted. The integration consisted of the insertion of a single cop y of the transgene, Flanking DNA was cloned, and mapping indicated that the genomic DNA on either side of the transgene was not contiguous in the wild -type mouse. Localization of unique markers from the two flanks indicated t hat both were in the proximal region of mouse chromosome 1, However, in the wild-type mouse the markers were separated by 6.3 cM, indicating a sizable rearrangement. Analysis of the mutant DNA indicated that the entire region between the markers was neither deleted nor simply inverted. Conclusions: These results are consistent with a complex rearrangement, including at lea st four breakpoints and spanning at least 6.3 cM, resulting from the integr ation of the transgene. This genomic rearrangement disrupted the function o f one or more genes critical to the maintenance of fluid homeostasis during development and the normal morphogenesis of the pars superior.