Insertion of the βGeo Promoter Trap into the Fem1c Gene of ROSA3 Mice

Abstract

ROSA3 mice were developed by retroviral insertion of the βGeo gene trap vector. Adult ROSA3 mice exhibit widespread expression of the trap gene in epithelial cells found in most organs. In the central nervous system the highest expression of βGeo is found in CA1 pyramidal cells of the hippocampus, Purkinje cells of the cerebellum, and ganglion cells of the retina. Characterization of the genomic insertion site for βGeo in ROSA3 mice shows that the trap vector is located in the first intron of Fem1c, a gene homologous to the sex-determining gene fem-1 of Caenorhabditis elegans. Transcription of the Rosa3 allele (R3) yields a spliced message that includes the first exon of Fem1c and the βGeo coding region. Although normal processing of the Fem1c transcript is disrupted in homozygous Rosa3 (Fem1c^R3/R3) mice, some tissues show low levels of a partially processed transcript containing exons 2 and 3. Since the entire coding region of Fem1c is located in these two exons, Fem1c^R3/R3 mice may still be able to express a putative FEM1C protein. To this extent, Fem1c^R3/R3 mice show no adverse effects in their sexual development or fertility or in the attenuation of neuronal cell death, another function that has been attributed to both fem-1 and a second mouse homolog, Fem1b. Examination of βGeo expression in ganglion cells after exposure to damaging stimuli indicates that protein levels are rapidly depleted prior to cell death, making the βGeo reporter gene a potentially useful marker to study early molecular events in damaged neurons.

This work was funded by grants from the National Eye Institute (R29 EY 12223 and R03 EY13790 to R.W.N.) and by the American Health Assistance Foundation, the Retina Research Foundation, the Glaucoma Foundation, and Research to Prevent Blindness, Inc.

We thank Phillip Soriano for generously providing the initial ROSA3 mice, Gretchen Poulsen for her expertise in processing brain tissue for enzyme histochemistry, and Heather Rae Pelzel for her assistance in conducing RT-PCR experiments.