Table 1.

Characterisation of induced pluripotent stem cells, photoreceptor cells and retinal pigment epithelium.

Techniques of Characterisation	Induced Pluripotent Stem Cells	Photoreceptor Cells	Retinal Pigment Epithelium
Morphology (light microscopy)	Flat colonies; small and round cells; high nuclear to cytoplasmic ratio	Located in outer nuclear layer; cell bodies with processes; inner and outer segments	Monolayer; pigmentation; hexagonal
Morphology (electron microscopy)	N/A	Outer segment discs, myoid and ellipsoid segments, connecting cilia, basal body	Apical microvilli, basal infoldings, tight-junctional complexes, pigment granules
Cellular markers (pluripotency)	Surface: SSEA-3, TRA-1-60, TRA-1-81; Others: NANOG, SOX2, OCT4	Loss of OCT3/4, SOX2, NANOG	Loss of OCT3/4, SOX2, NANOG
Cellular markers (progenitors/precursors)	N/A	PAX6, CHX10, CRX, OTX2, NRL	PAX6, MITF
Cellular markers (differentiated/mature)	N/A	Phototransduction: recoverin, transducing, cGMP phosphodiesterase, retinal guanylate cyclase, cyclic-nucleotide gated channel, rhodopsin, cone opsins (S or L/M), arrestin; visual cycle	Visual cycle: RPE65, RLBP1, CRALBP; phagocytosis: FAK, MERTK; pigmentation: tyrosinase; growth factor: VEGF, PEDF, PDGF; membrane: Na/K ATPase, ZO-1, BEST1
Molecular	RT-PCR, bisulphite sequence analysis	RT-PCR	RT-PCR
Functional (in vitro)	Embryoid body formation	Patch recordings; response to white flash	Phagocytosis assay/rhodopsin clearance; fluid transport, polarised secretion of growth factors (PEGF/VEGF); transepithelial resistance
Functional (in vivo)	Teratoma assay in animal to identify all three germ layers	Cell transplantation to demonstrate rescue of visual function	Cell transplantation (RCS rat) to demonstrate rescue of visual function
Genetic	Karyotyping sequencing to look for new mutations	Sequencing to check no new mutations	Sequencing to check no new mutations

RT-PCR, Reverse transcription polymerase chain reaction; RCS, Royal College of Surgeons.