Increased transgene expression by the mouse tyrosinase enhancer is restricted to neural crest‐derived pigment cells

Abstract

In this study, we have addressed the impact of the mouse tyrosinase enhancer on regulated expression from the mouse tyrosinase promoter during embryonic development. Stable and transient transgenic experiments using the reporter gene lacZ reveal that (1) expression is detected in neural crest-derived melanoblasts from E11.5 onward, (2) the enhancer does not increase transgenic expression in optic cup-derived pigment cells of the retinal pigment epithelium (RPE), and (3) expression in the telencephalon is not any longer detected. The importance of the enhancer for expression in pigment cells of the eye was further investigated in adult mice using an attenuated diphtheria toxin A gene. This demonstrated that in presence of the enhancer the transgene expression is specifically targeted to neural crest-derived melanocytes of the choroid and not, or slightly, to the RPE. This suggests that tyrosinase is differentially regulated in the two pigment cell lineages, and that this promoter can be used to target expression preferentially to the neural crest-derived melanocyte lineage.

Metastasizing Melanoma Formation Caused by Expression of Activated N-RasQ61K on an INK4a-Deficient Background

“…Similarly, melanocyte-specific expression of an oncogenic form of H-ras (H-Ras V12G ) on a INK4A À/À background induced melanomas with comparable latency and penetrance; however, in contrast to the model presented here, these remain amelanotic and nonmetastatic (11). Although N-Ras Q61K and H-Ras V12G transgenic constructs contain all the known tyrosinase regulatory elements including the distal control region (18), the melanoma phenotype might still be influenced by transgene expression or the integration site. However, the hyperpigmentation phenotype in the Tyr::N-ras Q61K line was intermediate compared with the other four founder mice generated but similar to the hyperpigmentation reported in the Tyr::H-ras V12G mice, suggesting a similar ras activity in both models.…”

“…We used the 6.1-kb promoter sequence of the mouse tyrosinase gene in combination with the 3.6-kb distal control region (18) to target expression of a mutant human N-ras gene (N-Ras Q61K ) to the melanocytic lineage (Fig. 1A).…”

“…Thus, skin melanocytes were removed from Tyr::N-Ras Q61K transgenic mice by a toxigenic approach expressing attenuated diphtheria toxin-A (Tyr::DT-A; ref. 18). Double transgenic mice were similar to Tyr::DT-A transgenic mice (Fig.…”

“…and polyadenylation sequences, cloned into the vector tyr(hs3.6/6.1)-lacZ (18). The gel-purified insert was injected into oocytes derived from superovulated B6D2F1 (F1[C57BL/6J Â DBA/2]) male and female matings.…”

“…To generate Tyr::N-Ras Q61K transgenic mice on an albino background, transgenics were bred to BALB/c mice for at least three generations. Toxigenic ablation of melanocytes was obtained by breeding the Tyr::N-Ras Q61K transgenic line to Tyr::DT-A (tyr(hs3.6/6.1)-DT-A) transgenic mice that express the attenuated diphtheria toxin-A gene specifically in melanocytes (18). To visualize melanocytes by h-galactosidase staining, Tyr::N-Ras Q61K transgenics were mated to Dct::lacZ (19) transgenic mice.…”