The JR5558 mouse (The Jackson Laboratory) harbors recessive mutations in unknown genes, which in the homozygous state, leads to numerous neovascular tufts originating from the choriocapillaris in the center to midperiphery of the fundus between P10 and P15 (
Fig. 1). The phenotype is more than 95% penetrant, is not influenced by sex, and nonocular phenotypes have not been observed. By fluorescein angiography,
9 the lesions were visible within 90 seconds of IP administration of sodium fluorescein, with leakage continuously increasing thereafter. By fundus color photography, the lesions were associated with multifocal pigmentary changes, but the neovasculature could not be observed (
Fig. 1A). Immunostaining of eyecups devoid of the retina using a vascular marker enabled more quantitative analyses and revealed that sCNV lesions increase in number and size with age (
Fig. 1B). The number of lesions peaks at 15 to 20 per eye at approximately P30, and after this time point some individual lesions coalesced into larger lesions (
Fig. 1C). Immunostaining, tracer studies, and histology all confirmed that the early lesions originated from, and were contiguous with the choriocapillaris, and they disrupted the RPE (
Figs. 2A–C,
Supplementary Figs. S1A, S2A). Electron microscopic images show that most CNV lesions grow and occupy the subretinal space, either apical to, or embedded within the RPE layer (
Fig. 2D,
Supplementary Fig. S3). Confocal imaging with a focus on the choriocapillaris-RPE interface revealed the accumulation of single cells positive for endothelial markers along the choriocapillaris vascular bed at P10 (
Figs. 3A–C). Small endothelial cell sprouts emanating from the RPE layer also appeared at P10, with the pioneer cells rich in filopodia (
Figs. 3D–F). Concordantly, the early choroidal vessel invasion is associated with changes in RPE phenotype, including depigmentation (
Figs. 1A,
2C), focal loss of ZO-1 expression, and disruption of RPE barrier function (
Supplementary Fig. S1). After P20 to P25, confocal imaging revealed that approximately 10% to 15% of the sCNV lesions grow into the ONL and anastomose with the deep retinal vascular plexus (
n = 20 eyes;
Figs. 3G,
3H).