transgenic line and single-cell transcriptomics reveal the origin of zebrafish intraspinal serotonergic neurons.

Sox transcription factors are crucial for vertebrate nervous system development. In zebrafish embryo, genes are expressed in neural progenitor cells and neurons of ventral spinal cord. Our recent study revealed that the loss of and function results in a significant decline of V2 subtype neurons (V2s). Using single-cell RNA sequencing, we analyzed the transcriptome of lineage progenitors and neurons in the zebrafish spinal cord at four time points during embryonic development, employing the ) line. In addition to previously characterized -expressing neurons, we discovered the expression of in late-developing intraspinal serotonergic neurons (ISNs). Developmental trajectory analysis suggests that ISNs arise from lateral floor plate (LFP) progenitor cells. Pharmacological inhibition of the Notch signaling pathway revealed its role in negatively regulating LFP progenitor cell differentiation into ISNs. Our findings highlight the zebrafish LFP as a progenitor domain for ISNs, alongside known Kolmer-Agduhr (KA) and V3 interneurons.