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Serotonergic neurons in the dorsal raphe (DR) nucleus are associated with several psychiatric disorders including depression and anxiety disorders, which often have a neurodevelopmental component. During embryonic development, GATA transcription factors GATA2 and GATA3 operate as serotonergic neuron fate selectors and regulate the differentiation of serotonergic neuron subtypes of DR. Here, we analyzed the requirement of GATA cofactor ZFPM1 in the development of serotonergic neurons usingZfpm1conditional mouse mutants. Our results demonstrated that, unlike the GATA factors, ZFPM1 is not essential for the early differentiation of serotonergic precursors in the embryonic rhombomere 1. In contrast, in perinatal and adult male and femaleZfpm1mutants, a lateral subpopulation of DR neurons (ventrolateral part of the DR) was lost, whereas the number of serotonergic neurons in a medial subpopulation (dorsal region of the medial DR) had increased. Additionally, adult male and femaleZfpm1mutants had reduced serotonin concentration in rostral brain areas and displayed increased anxiety-like behavior. Interestingly, femaleZfpm1mutant mice showed elevated contextual fear memory that was abolished with chronic fluoxetine treatment. Altogether, these results demonstrate the importance of ZFPM1 for the development of DR serotonergic neuron subtypes involved in mood regulation. It also suggests that the neuronal fate selector function of GATAs is modulated by their cofactors to refine the differentiation of neuronal subtypes.SIGNIFICANCE STATEMENTPredisposition to anxiety disorders has both a neurodevelopmental and a genetic basis. One of the brainstem nuclei involved in the regulation of anxiety is the dorsal raphe, which contains different subtypes of serotonergic neurons. We show that inactivation of a transcriptional cofactor ZFPM1 in mice results in a developmental failure of laterally located dorsal raphe serotonergic neurons and changes in serotonergic innervation of rostral brain regions. This leads to elevated anxiety-like behavior and contextual fear memory, alleviated by chronic fluoxetine treatment. Our work contributes to understanding the neurodevelopmental mechanisms that may be disturbed in the anxiety disorder.

Tegmental nuclei in the ventral midbrain and anterior hindbrain control motivated behavior, mood, memory and movement. These nuclei contain inhibitory GABAergic and excitatory glutamatergic neurons, whose molecular diversity and development remain largely unraveled. Many of the tegmental neurons originate in the embryonic ventral rhombomere 1, where the GABAergic fate is regulated by the transcription factor Tal1. Here, we used single-cell mRNA sequencing of the mouse ventral rhombomere 1 to characterize the Tal1-dependent and -independent neuronal precursors. We describe gene expression dynamics during bifurcation of the GABAergic and glutamatergic lineages and show how active Notch signaling promotes GABAergic fate selection in post-mitotic precursors. We identify GABAergic precursor subtypes that give rise to distinct tegmental nuclei and demonstrate that Sox14 and Zfpm2, two transcription factors downstream of Tal1, are necessary for the differentiation of specific tegmental GABAergic neurons. Our results provide a framework for understanding the development of cellular diversity in the tegmental nuclei