Variegated expression and delayed retinal pigmentation during development in transgenic mice with a deletion in the locus control region of the tyrosinase gene

Abstract

Deletion of the tyrosinase locus control region (LCR) in transgenic mice results in variegated expression in the skin. Here we investigate the pigmentation pattern of other tissues that express tyrosinase: iris, choroid, and retina in the same animals. A mosaic distribution of pigmentation appears in the iris and choroid. Interestingly, a markedly different mosaic pattern is found in the retina, where central areas contain little or no melanin while pigmentation rises to normal levels towards periphery. Further, there is a temporal delay in the initiation and accumulation of pigment in retinal pigmented epithelium (RPE) cells during development, and patterns of adult retinal melanisation in these mice appear arrested at a stage found in early embryogenesis in wild-type mice. These results demonstrate that the tyrosinase LCR is needed for the correct establishment and maintenance of this expression domain throughout development, but particularly during the later stages of retinal melanisation.

Efficient Generation of Transgenic Mice with Intact Yeast Artificial Chromosomes by Intracytoplasmic Sperm Injection1

“…All three YAC transgene-specific DNA markers and the characteristic pigmented phenotype were observed in the offspring of founder 1. The YAC YRT2⌬LCR construct carries a tyrosinase gene in which its locus control region (LCR) has been experimentally deleted, resulting in variegated expression in skin, coat, and eyes, as reported previously with analogous YAC constructs in mice [28], generated by PN microinjection [8,19]. This phenotype is recapitulated here as heavily pigmented eyes, with clear but low expression in skin (pigmented patches can be found in ears) and hair (very light gray coat color) (Fig.…”

“…For full-term development (of both one-and two-cell embryos, pronuclear injected plasmid, or ICSI-fertilized and pronuclear-injected YAC), embryos were transferred to oviducts of recipient females. Embryo transfer was performed as described previously [27,28].…”

Analysis of Transgene Integration

“…This is, for example, the case of the mouse tyrosinase locus, where an essential element, a locus control region (LCR), was found 15 kb upstream of its promoter and shown to be enough to sustain copy-numberdependent and position-independent transgene expression, with a per copy value comparable to that of the corresponding endogenous locus (Montoliu et al, 1996;Giraldo et al, 1999;Giraldo and Montoliu, 2002). In its absence, the lack of this LCR element triggered a variegated expression pattern of the transgenes, hence triggering de novo the appearance of the no-longer-compensated chromosomal position effects (Giménez et al, 2001(Giménez et al, , 2005.…”

Untitled

“…The LCR is necessary to establish the proper expression pattern of the mouse tyrosinase gene. The absence of the LCR resulted in weaker pigmentation, variegated expression in the melanocytes and RPE cells and delayed retinal pigmentation in transgenic mice [13]. Moreover, two binding boxes for nuclear factors within the LCR core, known as boxes A and B, were identified by in vitro analysis [14] and, recently, have been incorporated into a new boundary activity associated within the LCR region [15].…”