Human pluripotent stem cells have the potential to provide comprehensive model systems for the earliest stages of human ontogenesis. To serve in this capacity, these cells must undergo a targeted, stepwise differentiation process that follows a normal developmental timeline. Here we demonstrate the ability of both human embryonic stem cells (hESCs) and induced pluripotent stem (iPS) cells to meet these requirements for human retinogenesis. Upon differentiation, hESCs initially yielded a highly enriched population of early eye field cells. Thereafter, a subset of cells acquired features of advancing retinal differentiation in a sequence and time course that mimicked in vivo human retinal development. Application of this culture method to a human iPS cell line also generated retina-specific cell types at comparable times in vitro. Lastly, altering endogenous signaling during differentiation affected lineage-specific gene expression in a manner consistent with established mechanisms of early neural and retinal cell fate determination. These findings should aid in the investigation of the molecular events governing retinal specification from human pluripotent stem cells.

Differentiation methods for human induced pluripotent stem cells (hiPSCs) typically yield progeny from multiple tissue lineages, limiting their utility for drug testing and autologous cell transplantation. In particular, early retina and forebrain derivatives often intermingle in pluripotent stem cell cultures, owing to their shared ancestry and tightly coupled development. Here, we demonstrate that three-dimensional populations of retinal progenitor cells (RPCs) can be isolated from early forebrain populations in both human embryonic stem cell (hESC) and hiPSC cultures, providing a valuable tool for developmental, functional, and translational studies. Using our established protocol, we identified a transient population of optic vesicle-like (OV) structures that arose during a time period appropriate for normal human retinogenesis. These structures were independently cultured and analyzed to confirm their multipotent RPC status and capacity to produce physiologically responsive retinal cell types, including photoreceptors and retinal pigment epithelium (RPE). We then applied this method to hiPSCs derived from a patient with gyrate atrophy, a retinal degenerative disease affecting the RPE. RPE generated from these hiPSCs exhibited a disease-specific functional defect that could be corrected either by pharmacological means or following targeted gene repair. The production of OV-like populations from human pluripotent stem cells should facilitate the study of human retinal development and disease and advance the use of hiPSCs in personalized medicine.

Best disease (BD) is an inherited degenerative disease of the human macula that results in progressive and irreversible central vision loss. It is caused by mutations in the retinal pigment epithelium (RPE) gene BESTROPHIN1 (BEST1), which, through mechanism(s) that remain unclear, lead to the accumulation of subretinal fluid and autofluorescent waste products from shed photoreceptor outer segments (POSs). We employed human iPS cell (hiPSC) technology to generate RPE from BD patients and unaffected siblings in order to examine the cellular and molecular processes underlying this disease. Consistent with the clinical phenotype of BD, RPE from mutant hiPSCs displayed disrupted fluid flux and increased accrual of autofluorescent material after long-term POS feeding when compared with hiPSC-RPE from unaffected siblings. On a molecular level, RHODOPSIN degradation after POS feeding was delayed in BD hiPSC-RPE relative to unaffected sibling hiPSC-RPE, directly implicating impaired POS handling in the pathophysiology of the disease. In addition, stimulated calcium responses differed between BD and normal sibling hiPSC-RPE, as did oxidative stress levels after chronic POS feeding. Subcellular localization, fractionation and co-immunoprecipitation experiments in hiPSC-RPE and human prenatal RPE further linked BEST1 to the regulation and release of endoplasmic reticulum calcium stores. Since calcium signaling and oxidative stress are critical regulators of fluid flow and protein degradation, these findings likely contribute to the clinical picture of BD. In a larger context, this report demonstrates the potential to use patient-specific hiPSCs to model and study maculopathies, an important class of blinding disorders in humans.

We demonstrate for the first time that human blood-derived iPSCs can generate retinal cell types, providing a highly convenient donor cell source for iPSC-based retinal studies. We also show that cultured TiPSC-OVs have the capacity to self-assemble into rudimentary neuroretinal structures and express markers indicative of chemical and electrical synapses.

Human neural precursor cells grown in culture provide a source of tissue for drug screening, developmental studies and cell therapy. However, mechanisms underlying their growth and differentiation are poorly understood. We show that epidermal growth factor (EGF) responsive precursors derived from the developing human cortex undergo senescence after 30-40 population doublings. Leukemia inhibitory factor (LIF) increased overall expansion rates, prevented senescence and allowed the growth of a long-term self renewing neural stem cell (ltNSC ctx ) for up to 110 population doublings. We established basal gene expression in ltNSC ctx using Affymetrix oligonucleotide microarrays that delineated specific members of important growth factor and signaling families consistently expressed across three separate lines. Following LIF withdrawal, 200 genes showed significant decreases. Protein analysis confirmed LIF-regulated expression of glial fibrillary acidic protein, CD44, and major histocompatibility complex I. This study provides the first molecular profile of human ltNSC ctx cultures capable of long-term self renewal, and reveals specific sets of genes that are directly or indirectly regulated by LIF. Keywords: epidermal growth factor, leukemia inhibitory factor, microarray, neural stem cells, neurosphere. Multi-potent precursor cells derived from the developing or adult brain can be isolated in culture and expanded in the presence of mitogens (for review, see McKay 1997;Gage 2000). In some of these techniques, the cells are grown in free-floating aggregates termed 'neurospheres' (Reynolds et al. 1992). Neurospheres have also been generated from human post-mortem fetal tissues using a variety of growth factors and culturing methods (Svendsen et al. 1996;Chalmers-Redman et al. 1997;Svendsen et al. 1998;Carpenter et al. 1999;Vescovi et al. 1999). Neurospheres have great potential for possible cell therapy applications and as a model for mechanisms of human development and disease. For example, cells derived from neurospheres can migrate and integrate after transplantation into the developing or adult brain (Svendsen et al. 1996;Svendsen et al. 1997a;Flax et al. 1998;Fricker et al. 1999;Rosser et al. 2000;Qu et al. 2001;Ostenfeld et al. 2002b;Wu et al. 2002). We have recently shown that neurospheres isolated from Down syndrome fetal tissue have specific genetic deficits and undergo reduced neurogenesis at later passages (Bahn et al. 2002). However, these intriguing findings underscore the fact that very little is known about the temporal pattern of growth in these cultures or the exact cellular composition of neurospheres.Where clonal analysis has been performed, a number of cells within rodent neurospheres have been shown to self Abbreviations used: BDNF, brain-derived neurtrophic factor; BMP, bone morphogenetic protein; BrdU, 5-bromo-2¢-deoxyuridine; CNTF, ciliary neurotrophic factor; DMEM, Dulbecco's modified Eagle's medium; EFN, ephrin; EGF, epidermal growth factor; EST, expressed sequence tag; FGF-2, basic fibr...