RPE dysplasia with retinal duplication in a mutant mouse strain

Staphyloma in a cat

A unilateral scleral staphyloma in an 18-month-old, female spayed Domestic Short-haired cat was treated with excision, primary closure and fascial graft. Other ocular abnormalities noted on examination included iris coloboma, anterior cortical cataract, focal lens equator flattening and retinal dysplasia. The staphyloma was presumed to be congenital in origin.

Influence of destruction of retina-RPE complex on the proliferation of scleral chondrocytes in chicks

We studied the role of the retina-retinal pigment epithelium (RPE) complex in the proliferation of scleral chondrocytes in chicks. Seventy-two chicks were allocated to one of four groups: intravitreal gentamicin (400 microg) injection (destruction of retina-RPE complex); intravitreal gentamicin injection with goggling; goggling only (form-deprivation myopia); and intravitreal saline injection (control). The chicks were killed and retina-RPE complexes were harvested under a microscope. Retina-RPE complexes were then co-cultured with primary culture of first day scleral chondrocytes in Transwell-COL co-culture systems (Costar), with two different pore sizes (0.4 and 3.0 microm) and serum-deprivation medium. An MTT assay was performed at A550 after 4 days. In the 0.4 microm pore size system, the absorbency at A550 showed no differences between groups. However, in the 3.0 microm pore size system, the absorbency at A550s in the intravitreal gentamicin groups was significantly lower than in the control and the goggle groups (p<0.05), indicating that destruction of the retina-RPE complex inhibited chondrocyte proliferation. The absorbency in the goggle group was higher than in the control group (p<0.05). These results indicate that the retina-RPE complex exerts a positive effect on the proliferation of scleral chondrocytes via a molecule sized between 0.4.and 3.0 microm in diameter.

Retinal dysplasia and degeneration in RARbeta2/RARgamma2 compound mutant mice

The eye is the organ whose development is the most frequently altered in response to maternal vitamin A deficiency [VAD; Warkany, J. and Schraffenberger, S. (1946). Archs Ophthalmol. 35, 150–169]. With the exception of prenatal retinal dysplasia, all the ocular abnormalities of the fetal VAD syndrome are recapitulated in mouse mutants lacking either RARalpha and RARbeta2, RARalpha and RARgamma, RARgamma and RARbeta2, or RXRalpha [Lohnes, D., Mark, M., Mendelsohn, C., Dolle, P., Dierich, A., Gorry, P., Gansmuller, A. and Chambon, P. (1994) Development 120, 2723–2748; Mendelsohn, C., Lohnes, D., Decimo, D., Lufkin, T., LeMeur, M., Chambon, P. and Mark, M. (1994) Development 120, 2749–2771; Kastner, P., Grondona, J. Mark, M., Gansmuller, A., LeMeur, M., Decimo, D., Vonesch, J.L., Dolle, P. and Chambon, P. (1994) Cell 78, 987–1003], thus demonstrating that retinoic acid (RA) is the active vitamin A metabolite during prenatal eye morphogenesis. Whether retinoids are also involved in postnatal eye development could not be investigated, as VAD newborns are not viable and the above RAR double null mutants and RXRalpha null mutants died in utero or at birth. We report here the generation of viable RARbeta2/RARgamma2 double null mutant mice, which exhibit several eye defects. The neural retina of newborn RARbeta2gamma2 mutants is thinner than normal due to a reduced rate of cell proliferation, and from day 4 shows multiple foci of disorganization of its layers. These RARbeta2gamma2 mutants represent the first genetically characterized model of retinal dysplasia and their phenotype demonstrates that RARs, and therefore RA, are required for retinal histogenesis. The RARbeta2gamma2 retinal pigment epithelium (RPE) cells display histological and/or ultrastructural alterations and/or fail to express cellular retinol binding protein I (CRBPI). Taken altogether, the early onset of the RPE histological defects and their striking colocalisation with areas of the neural retina displaying a faulty laminar organization, a reduced neuroblastic proliferation, and a lack of photoreceptor differentiation and/or increased apoptosis, make the RPE a likely target tissue of the RARbeta2gamma2 double null mutation. A degeneration of the adult neural retina, which may similarly be secondary to a defective RPE, is also observed in these mutants, thus demonstrating an essential role of RA in the survival of retinal cells. Moreover, all RARbeta2gamma2 mutants display defects in structures derived from the periocular mesenchyme including local agenesis of the choroid and of the sclera, small eyelids, and a persistence of the primary mesenchymal vitreous body. A majority of the RARbeta2 single null mutants also exhibit this latter defect, thus demonstrating that the RARbeta2 isoform plays a unique role in the formation of the definitive vitreous body.