• Deregulation of zebrafish Jagn1 disrupts neutrophil development, affecting steady state granulopoiesis.

  • Activation of unfolded protein response (UPR) and apoptosis alone is insufficient to induce neutropenia in zebrafish

A variety of autosomal recessive mutations in the JAGN1 gene cause severe congenital neutropenia (CN). However, the underlying pathomechanism remains poorly understood, mainly due to the limited availability of primary hematopoietic stem cells from JAGN1-CN patients and the absence of animal models. In this study, we aimed to address these limitations by establishing a zebrafish model of JAGN1-CN. We found two paralogs of the human JAGN1 gene, jagn1a and jagn1b, which play distinct roles during zebrafish hematopoiesis. Using various approaches such as morpholino-based knockdown, CRISPR/Cas9-based gene-editing, and misexpression of a jagn1b harboring a specific human mutation, we successfully developed neutropenia while leaving other hematopoietic lineages unaffected. Further analysis of our model revealed significant upregulation of apoptosis and genes involved in unfolded protein response (UPR). However, neither UPR nor apoptosis is the primary mechanism leading to neutropenia in zebrafish. Instead, Jagn1b has a critical role in G-CSFR signaling and steady-state granulopoiesis, shedding light on the pathogenesis of neutropenia associated with JAGN1 mutations. The establishment of a zebrafish model for JAGN1-CN represents a significant advancement in understanding the specific pathological pathways underlying the disease. This model provides a valuable in vivo tool for further investigation and exploration of potential therapeutic strategies.

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