A Zebrafish Model for Severe Congenital Neutropenia with Jagn1b-Deficiency

Severe congenital neutropenia (CN) is a bone marrow failure characterized by an impaired neutrophil development. This disease can be caused by different germline mutations, which one of them is Jagunal homolog 1 (JAGN1). CN patients are prone to develop life-threatening infections from birth on and the treatment of choice is recombinant human granulocyte colony-stimulating factor (rhG-CSF). However, patients with JAGN1 deficiency poorly respond to this treatment. Therefore, the development of new therapeutic strategies to treat this disease is essential. Thus far, lack of an animal model was the main limitation to study the function of JAGN1 in neutropenia and perform high-throughput compound screening. In this work, we studied the role of jagn1b in zebrafish granulopoiesis and hematopoiesis. Two different approaches were used. First, we injected antisense morpholino that efficiently blocked the translation of jagn1b mRNA. As a second approach, we used the CRISPR-Cas9 technique to introduce mutations in the zebrafish jagn1b gene and analyzed the crispants. Both of these approaches were tested in wild-type embryos as well as the transgenic mpo:GFP reporter line, in which neutrophils are labeled with GFP. Our results showed that interference with Jagn1b reduced the number of neutrophils, without affecting the early myelopoiesis and monocytes/macrophages. Further analysis revealed that apoptosis was enhanced in embryos injected with the jagn1b morpholino, however, this effect was not restricted to the hematopoietic tissues. Our results also suggested that unfolded protein response (UPR) was activated because the expression levels of genes involved in this pathway such as chop, atf4a and atf4b were significantly upregulated in the jagn1b morphants, when compared with the wild-type counterparts. Overall, we have successfully established a novel in vivo model for studying the role of JAGN1 in granulopoiesis, and the possible role of Jagn1b in UPR response might be useful to find new targets for the development of therapeutic strategies for CN.