Transgenic pigs expressing rhodopsin PRO347LEU mutation exhibit retinal degeneration

Purpose. The goal of this study was to determine whether transgenic pigs expressing a rhodopsin Pro347Leu mutation would exhibit retinal degeneration characteristic of retinitis pigmentosa (RP). Methods. A pig rhodopsin gene (Pro347Leu) was microinjected into pig embryos. Transgenic pigs were reared to sexual maturity and mated. For expression analysis, retinal mRNA was extracted and cDNA fragments produced with RT-PCR for sequence analysis. Retinal degeneration was studied by histologic analysis. Results. A transgenic founder male pig (HP-1) transmitted the transgene to 47 of 58 offspring (81%). Southern analysis of offspring was consistent with a hypothesis of two integration sites on different chromosomes with an estimated 5 copies of the transgene at each site. Two lines corresponding to these two integration sites respectively were established: HP-Type 1 and HP-Type 2. Expression of the transgene was confirmed in a 5-week old HP-Type 2 pig; in this pig, the ratio of normal to mutant rhodopsin was approximately 1:4. The youngest HP-Type 2 pigs we have studied by histology were 6 weeks old. In the retinas of these pigs, most of the rods had disappeared; in contrast, most of the cones were present. In the 6-month old pigs, however, only 10-20% of the cones remained. Analysis of HP-Type 1 pigs at comparable ages yielded similar results. Transgenic negative littermates had normal retinas. Conclusions. Pro347Leu transgenic pigs exhibit rod-cone degeneration, which is characteristic of RP. Our results also agree with previously observed retinal degeneration in Pro347Leu transgenic mice. Unlike the mouse retina, the transgenic pig retina has an abundance of cones, and thus offers an ideal model for RP therapeutic research that aims at rescuing the cones, which are the cells critical for human vision.

Duke Scholars

Author Fulton Wong Ophthalmology