A Transgenic Mouse Model with Inducible Tyrosinase Gene Expression Using the Tetracycline (Tet‐on) System Allows Regulated Rescue of Abnormal Chiasmatic Projections Found in Albinism

Abstract

Congenital defects in retinal pigmentation, as in oculocutaneous albinism Type I (OCA1), where tyrosinase is defective, result in visual abnormalities affecting the retina and pathways into the brain. Transgenic animals expressing a functional tyrosinase gene on an albino genetic background display a correction of all these abnormalities, implicating a functional role for tyrosinase in normal retinal development. To address the function of tyrosinase in the development of the mammalian visual system, we have generated a transgenic mouse model with inducible expression of the tyrosinase gene using the tetracycline (TET-ON) system. We have produced two types of transgenic mice: first, mice expressing the transactivator rtTA chimeric protein under the control of mouse tyrosinase promoter and its locus control region (LCR), and; second, transgenic mice expressing a mouse tyrosinase cDNA construct driven by a minimal promoter inducible by rtTA in the presence of doxycycline. Inducible experiments have been carried out with selected double transgenic mouse lines. Tyrosinase expression has been induced from early embryo development and its impact assessed with histological and biochemical methods in heterozygous and homozygous double transgenic individuals. We have found an increase of tyrosinase activity in the eyes of induced animals, compared with littermate controls. However, there was significant variability in the activation of this gene, as reported in analogous experiments. In spite of this, we could observe corrected uncrossed chiasmatic pathways, decreased in albinism, in animals induced from their first gestational week. These mice could be instrumental in revealing the role of tyrosinase in mammalian visual development.

Regional abnormalities in retinal development are associated with local ocular hypopigmentation

“…Statistically significant differences (multiple-comparisons test: ANOVA post hoc with Bonferroni correction) are indicated as follows: **P Ͻ 0.01, ***P Ͻ 0.001. edly decreased. In only 2 of 13 (ϳ15%) albino NMRI animals did we observe any DiI-labelled ipsilateral projecting axons (Gimenez et al, 2004). In contrast, DiI-labelled ipsilateral axonal projections were observed in 6 of 9 (ϳ67%) YRT4 transgenic mice examined.…”

“…fetuses to label anterogradely this pathway . Ipsilateral axonal projections could be easily detected in all (6/6) pigmented C57BL/6J and (5/5) YRT2 transgenic mice examined (Gimenez et al, 2004). However, in albino NMRI mice, the magnitude of this projection was mark- Fig.…”

“…The methods employed for pathway tracing were the same as those used by and , as reported recently (Gimenez et al, 2004). Embryos at 18.5 d.p.c.…”

“…The failure of the RPE to pigment frequently is due to mutations in the tyrosinase gene, whose enzymatic product catalyses the oxidation of L-tyrosine to melanin precursors through L-DOPA (del Marmol and Beermann, 1996;Solano and Garcia-Borron, 1998;Gimenez et al, 2003). All visual abnormalities found in albinism are corrected in transgenic animals carrying the entire tyrosinase gene, suggesting a direct or indirect role of this enzyme in normal retinal development (Jeffery et al, 1994Gimenez et al, 2004). It has been proposed that L-DOPA, an early intermediate metabolite in the synthetic pathway of melanin, may be the critical agent, insofar as it is known to shorten the length of the cell cycle and reduce the number of mitotic figures in the retina (Akeo et al, 1989(Akeo et al, , 1994Ilia and Jeffery, 1999).…”

Retrovirus-mediated tk gene therapy of implanted human breast cancer in nude mice under the regulation of Tet-On

“…[12][13][14] Indeed, the low cytotoxicity of tetracycline, as well as that of its derivatives, and its high affinity for TetR have enabled the use of this antibiotic at concentrations that cause no appreciable adverse effects in transgenic animals. [15][16][17] We previously reported that the expression of the suicide gene HSVtk was regulated by Dox in MCF-7 cells that were cotransfected with pRevTet-On and pRevTRE/ HSVtk plasmids, and the antitumor effect was observed in severe combined immune deficiency (SCID) mice bearing breast cancer xenografts. 18 On the basis of these findings, we asked whether retrovirus-mediated suicide gene transfer could be used to treat tumors in a more clinically relevant setting.…”