Rlbp1 promoter drives robust Müller glial GFP expression in transgenic mice.

PURPOSE. Muller glia are essential for maintaining retinal homeostasis and exhibit neuroprotective and deleterious responses during retinal degeneration. Having the ability to visualize and genetically manipulate Muller glia in vivo will facilitate a better understanding of how these cells contribute to these processes. The goal of this study was to determine whether regulatory elements of the retinaldehyde binding protein 1 (Rlbp1; formerly Cralbp) gene can drive robust Muller glial gene expression in vivo. METHODS. Transgenic mice were generated by pronuclear injection of a construct carrying a 3-kilobase (kb) region of the Rlbp1 gene and 5'-flanking sequences linked to the enhanced green fluorescent protein (GFP) cDNA. GFP expression was analyzed by immunohistology in regions of the central nervous system in which RLBP1 protein is expressed, in retinas from wild-type and retinal degeneration 1 (rd1) mice, and during retinal development. RESULTS. Three transgenic lines were generated, and the one with the strongest and most consistent GFP expression was characterized further. Miiller glia displayed robust GFP expression at all postnatal developmental stages and in the rd1 retina. Onset of expression occurred by birth in retinal progenitor cells. CONCLUSIONS. Regulatory elements in a restricted region of the Rlbp1 gene are sufficient to drive GFP expression in vivo. This transgenic line provides robust GFP expression that can be used to visualize retinal progenitor cells during postnatal development and Muller glia during their differentiation and in the healthy or degenerating adult retina.