RS1 and retinoblastoma: Searching for an in vitro model system applicable for analysing the influence of retinoschisin on MAP kinase signalling, we tested different retinal cells including murine microglial cell line BV‐2, human RPE‐derived cell line ARPE‐19, the human retinoblastoma cell lines Y‐79 and Weri‐Rb1 for their capacity to bind retinoschisin (Fig. 2A).