A microRNA feedback circuit in midbrain dopamine neurons MicroRNAs (miRNAs) are small non-coding RNA molecules that regulate gene expression post-transcriptionally. This study investigates the role of miRNAs in the terminal differentiation, function, and survival of midbrain dopamine neurons (DNs) in mammals, focusing on miR-133b, which is specifically expressed in midbrain DNs and is deficient in Parkinson's disease (PD) tissue. The research reveals that miR-133b functions within a negative feedback circuit with the transcription factor Pitx3, which regulates the maturation and function of DNs. The study used in vitro models, including the differentiation of murine embryonic stem (ES) cells into DNs, to examine the role of miRNAs. Cre-mediated deletion of the Dicer gene, essential for miRNA processing, led to a significant reduction in dopamine neuron accumulation, as well as increased apoptosis and reduced neurogenesis. Transfection of midbrain-derived small RNAs rescued the Dicer deletion phenotype, suggesting that miRNAs are crucial for midbrain DN terminal differentiation and survival. Further analysis of PD patient samples and models of dopamine neuron deficiency revealed that miR-133b is specifically deficient in PD samples and in models of dopamine neuron loss. miR-133b was found to be regulated by Pitx3, which is a transcription factor involved in DN development. Overexpression of Pitx3 led to increased miR-133b expression, while miR-133b overexpression reduced the expression of DN markers such as DAT and TH, indicating a regulatory role in DN maturation and function. The study also showed that miR-133b targets the 3′-UTR of Pitx3, leading to post-transcriptional regulation of Pitx3 expression. This forms a feedback loop where Pitx3 activates miR-133b expression, which in turn suppresses Pitx3. This feedback mechanism is crucial for the terminal differentiation and maintenance of DNs, and its disruption is associated with PD pathology. The findings highlight the importance of miRNA regulation in the development and survival of midbrain dopamine neurons.A microRNA feedback circuit in midbrain dopamine neurons MicroRNAs (miRNAs) are small non-coding RNA molecules that regulate gene expression post-transcriptionally. This study investigates the role of miRNAs in the terminal differentiation, function, and survival of midbrain dopamine neurons (DNs) in mammals, focusing on miR-133b, which is specifically expressed in midbrain DNs and is deficient in Parkinson's disease (PD) tissue. The research reveals that miR-133b functions within a negative feedback circuit with the transcription factor Pitx3, which regulates the maturation and function of DNs. The study used in vitro models, including the differentiation of murine embryonic stem (ES) cells into DNs, to examine the role of miRNAs. Cre-mediated deletion of the Dicer gene, essential for miRNA processing, led to a significant reduction in dopamine neuron accumulation, as well as increased apoptosis and reduced neurogenesis. Transfection of midbrain-derived small RNAs rescued the Dicer deletion phenotype, suggesting that miRNAs are crucial for midbrain DN terminal differentiation and survival. Further analysis of PD patient samples and models of dopamine neuron deficiency revealed that miR-133b is specifically deficient in PD samples and in models of dopamine neuron loss. miR-133b was found to be regulated by Pitx3, which is a transcription factor involved in DN development. Overexpression of Pitx3 led to increased miR-133b expression, while miR-133b overexpression reduced the expression of DN markers such as DAT and TH, indicating a regulatory role in DN maturation and function. The study also showed that miR-133b targets the 3′-UTR of Pitx3, leading to post-transcriptional regulation of Pitx3 expression. This forms a feedback loop where Pitx3 activates miR-133b expression, which in turn suppresses Pitx3. This feedback mechanism is crucial for the terminal differentiation and maintenance of DNs, and its disruption is associated with PD pathology. The findings highlight the importance of miRNA regulation in the development and survival of midbrain dopamine neurons.