AbstractRetinal organoids derived from inducible pluripotent stem cells were used to gain insight into the role of l-DOPA during human retinal development. Dopaminergic gene expression was indicated by assessing two dopamine receptors (DRD1 andDRD2), DOPA decarboxylase (DDC), and tyrosine hydroxylase (TH) via quantitative reverse transcription-polymerase chain reaction at various developmental stages. TH transcript levels started to express around day (D) 42, reached maximal expression ∼D63 and then decreased thereafter. At D29, proliferating retinal progenitors expressedDRD1, DRD2, andDDCat various levels of mRNA throughout the day. In the presence of l-DOPA, D29 retinal organoids expressedDRD1butDRD2mRNA expression was suppressed. Additionally, l-DOPA upregulatedTHmRNA prior to dopaminergic amacrine cell (DAC) development. After the appearance of DACs, l-DOPA phase shifted expression ofDRD2and synchronized mRNA expression ofDDC, DRD2, andTH. The present results suggest unique mechanisms for DA signaling at different stages of development in the human retina.