Fluorescence in situ hybridization has been used to demonstrate the differential distribution of interspersed repetitive elements in the genome ofMus musculus domesticus. Hybridization with a mouse long interspersed element sequence results in a sharp, highly reproducible banding pattern on metaphase chromosomes, which is quite similar to Giemsa banding for all chromosomes except 7 and X. The families of short interspersed elements, B1 and B2, preferentially cluster in the R, or reverse, bands. There is no evidence of any interspersed repeat present in the centromeric heterochromatic regions. Both the long interspersed element and B2 probes give banding patterns suitable for karyotype analysis. Simultaneous hybridization of the biotinylated long interspersed element probe and a digoxigenin-labeled cosmid to metaphase spreads allows rapid localization of a probe of interest to a particular cytogenetic band on a chromosome.

The semidominant mutation Krd (kidney and retinal defects) was identified in transgenic line Tg8052. Krd/+ mice have a high incidence of kidney defects including aplastic, hypoplastic, and cystic kidneys. Retinal defects in Krd/+ mice include abnormal electroretinograms and a reduction of cell numbers that is most extreme in the inner cell and ganglion layers. Viability of Krd/+ mice is strongly influenced by genetic background, and growth retardation is observed in young animals. Homozygosity results in early embryonic lethality. Fluorescence in situ hybridization of a transgene-specific probe localized the insertion site to the distal region of mouse Chromosome 19. The sequence of the insertion site revealed transgene insertion into a LINE element with deletion of a single nucleotide from the 3' terminus of the transgene. A polymorphic microsatellite, D19Umi1, was identified in a junction clone and mapped in several large crosses. D19Umi1 is located 1.7 +/- 1.0 cM distal to Pax2, which encodes a paired type transcription factor expressed in embryonic kidney and eye. Deletion of Pax2 from the transgenic chromosome was demonstrated by Southern analysis of genomic DNA from (Krd/+ x SPRET/Ei)F1 mice. Additional genetic and molecular data are consistent with an approximately 7-cM deletion that includes the loci stearoyl CoA desaturase (Scd1), pale ear (ep), D19Mit17, D19Mit24, D19Mit27, D19Mit11, and Pax2. This deletion, Del(19)TgN8052Mm, will be useful for genetic and functional studies of this region of mouse Chromosome 19.

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