<b>Unveiling Novel Genes that Regulate Neutrophil Migration</b>

<p dir="ltr">Neutrophils are the most abundant white blood cells in humans and play a central role in innate immunity by rapidly migrating to sites of infection or injury, secreting pro-inflammatory mediators, and eliminating pathogens through mechanisms such as phagocytosis, degranulation, reactive oxygen species (ROS) production, and neutrophil extracellular trap formation. While essential for host defense, dysregulated neutrophil activity can drive inflammatory and autoimmune diseases, as well as cancer progression. Therefore, understanding the molecular regulation of neutrophil migration is critical for developing targeted therapies.</p><p dir="ltr">MicroRNAs (miRs) - short, non-coding RNAs that regulate gene expression - have emerged as key modulators of immune cell function. However, the specific roles of individual miRs in neutrophil migration remain poorly understood. In this study, we identify miR-190 as a novel regulator of neutrophil motility using the zebrafish model system. Overexpression of miR-190 in transgenic zebrafish significantly impaired neutrophil recruitment to wound sites and reduced neutrophil velocity, indicating a suppressive effect on migration.</p><p dir="ltr">To uncover the mechanism behind this phenotype, we integrated RNA sequencing with CRISPR-Cas9–mediated gene knockouts to screen for miR-190 target genes that affect neutrophil behavior. Among the candidates, rabep1—encoding Rabaptin-5, a Rab GTPase effector—emerged as the most significant contributor to the observed motility defects. Neutrophil-specific rabep1 knockout zebrafish lines recapitulated the miR-190 overexpression phenotype, confirming rabep1 as a key mediator of neutrophil migration downstream of miR-190.</p><p dir="ltr">Extending these findings to human biology, we knocked down RABEP1 in differentiated HL-60 (dHL-60) neutrophil-like cells. Consistent with our <i>in vivo</i> data, RABEP1-deficient cells exhibited impaired migration and accumulation of internalized endosomes, suggesting disrupted endocytic recycling. As Rab4 and Rab5 are known regulators of vesicular trafficking and receptor recycling, these results implicate RABEP1 as a key mediator of the endosome-plasma membrane recycling process necessary for precise neutrophil migration.</p><p dir="ltr">RABEP1 has been implicated in the regulation of migration in several cell types, including tumor cells, mast cells, and neuronal cells, primarily through its role in vesicular trafficking and receptor recycling. However, its specific involvement in neutrophil migration remains to be elucidated. Our study is the first to identify the miR-190–RABEP1 axis that regulates neutrophil motility across vertebrate systems. By combining genetic tools in zebrafish with human cell-based assays, we reveal a previously uncharacterized molecular pathway governing neutrophil migration. These findings not only advance our understanding of innate immune regulation but also open new avenues for therapeutic strategies targeting aberrant leukocyte activity in inflammatory and immune-related diseases.</p>