Irish setter dogs affected with a rod/cone dysplasia (locus designation, rcdl) display markedly elevated levels of retinal cGMP during postnatal development. The photoreceptor degeneration commences =25 days after birth and culminates at about 1 year when the population of rods and cones is depleted. A histone-sensitive retinal cGMP phospho- subunit by 49 residues, thus removing the C-terminal domain that is required for posttranslational processing and membrane association. These results suggest that the redl gene encodes the rod photoreceptor PDE 13 subunit and that a nonsense mutation in this gene is responsible for the production of a nonfunctional rod PDE and the photoreceptor degeneration in the rcdl/rcdl Irish setter dogs.The Irish setter rod/cone dysplasia leading to a rapidly progressing loss of photoreceptors (1) is inherited as an autosomal recessive trait (genetic locus, rcdl). The early onset of the photoreceptor degeneration has been well defined by morphological and biochemical studies (2-4). Clin-ically, the disorder is grouped within a famnily of related canine retinal degenerations which are termed progressive retinal atrophies (5). In affected dogs, retina and photoreceptor development appears normal until 13 days of age (4), but subsequent development of rod photoreceptor cells is arrested. Rod photoreceptor degeneration is evident by 1 month of age; nearly all of the rod photoreceptors have degenerated by 5 months, and cone photoreceptor degeneration is completed by about 1 year (for review, see refs. 6 and 7).The earliest known biochemical manifestation of the rcdl phenotype is a rapid accumulation of cGMP to levels that are about 10-fold above those of age-matched controls (2-4, 8). These features are reminiscent of the phenotype seen in the rd mouse in which a nonsense mutation in exon 7 ofthe cGMP phosphodiesterase (PDE) (-subunit gene prevents the formation of a functional enzyme (9) leading to elevated cGMP levels and a rapid rod photoreceptor degeneration. Earlier studies of retinas from normal and affected Irish setters showed that the a and 'y mRNAs of affected dog PDE were of normal size and abundance (10), whereas the /-subunit mRNA level appeared to be reduced (11,12). This finding, similar to that in the rd mouse, suggests a defect in the dog PDE l3-subunit gene. Since a previous study showed the presence of a histone sensitive cGMP PDE activity in affected, immature Irish setter retinas (13), we reinvestigated its origin by an HPLC method which is capable of separating rod and cone PDEs (14). In this paper we identify the residual PDE activity in affected Irish setter retinas as comigrating with cone PDE, whereas rod PDE activity is completely absent. We further provide evidence that a functional /3 subunit is not produced in affected retinas and that a nonsense mutation near the C-terminal end of the /-subunit gene leads to truncation and destabilization of the gene product,

To generate animal models of retinoblastoma that closely resemble metastatic and nonmetastatic human disease for the purposes of examining tumor biology and developing alternate treatments, human retinoblastoma cell lines were injected into the vitreal cavities of immunodeficient mice. Two reproducible animal models with contrasting biological behaviors analogous to human retinoblastoma have been developed. The Y79 retinoblastoma model demonstrated specific tumor evolution similar to that seen in human invasive and metastatic disease. Y79 retinoblastoma cells formed intraocular tumors that were initially confined to the vitreal cavity.

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