New genome-editing approaches, such as the CRISPR/Cas system, have opened up great opportunities to insert or delete genes at targeted loci and have revolutionized genetics in model organisms like the zebrafish. The Cre-loxp recombination system is widely used to activate or inactivate genes with high spatial and temporal specificity. Using a CRISPR/Cas9-mediated knock-in strategy, we inserted a zebrafish codon-optimized CreERT2 transgene at the otx2 gene locus to generate a conditional Cre-driver line.We chose otx2 as it is a patterning gene of the anterior neural plate that is expressed during early development. By knocking in CreERT2 upstream of the endogenous ATG of otx2, we utilized this gene’s native promoter and enhancer elements to perfectly match CreERT2 and endogenous otx2 expression patterns. Next, by combining this novel driver line with a Cre-dependent reporter line, we show that only in the presence of tamoxifen can efficient Cre-loxp-mediated recombination be achieved in the anterior neural plate-derived tissues like the telencephalon, the eye and the optic tectum. Our results imply that the otx2:CreERT2 transgenic fish will be a valuable tool for lineage tracing and conditional mutant studies in larval and adult zebrafish.

Interleukin-10 (IL-10) is an important regulator of immune responses secreted by different cell types. Previous results from our group suggested that the biological effects of this cytokine critically depend on its cellular source. Recent studies reported IL-10 dependent immunosuppressive functions of a specialized subset of regulatory B cells and mast cells. These results relied on adoptive cell transfers, a technique which can potentially introduce artifacts. Therefore, we aimed to readdress these questions in independent models using IL-10 transcriptional reporter mice and various conditional IL-10 mutant mice. Findings in IL-10 reporter system suggested prominent IL-10 transcription in regulatory B cells upon LPS administration. Exposure of mice to contact allergen revealed robust reporter expression in CD8 T cells, moderate to mild reporter expression in CD4 T cells and dendritic cells (DC) respectively, and lack of reporter expression in B cells, mast cells and NK cells in allergen challenged ears. We generated cell-type specific IL-10 mutants by Cre/LoxP-mediated conditional gene inactivation. Efficiency and specificity of Cre-mediated recombination was demonstrated by Southern blot and PCR methods. Various immunogenic challenges in conditional IL-10 mutants did not reveal a role for B cell-derived IL-10 in restraining innate TLR or T cell-dependent inflammatory responses. Likewise, mice with selective inactivation of the il10 gene in mast cells exhibited normal CHS responses and unaltered immune response to CpG oligodeoxynucleotides. On the other hand, DC-specific IL-10 mutants developed excessive inflammatory responses to contact allergens, while innate responses to TLR ligands were not altered. This indicates a non-redundant role for DC-derived IL-10 in contact allergy. Thus, the conditional IL-10 ‘‘knockout’’ mice combined with the novel transcriptional IL-10 reporter system can serve as ideal tools to understand the cell-type specific contributions to IL-10-mediated immune regulation.

Interleukin-10 (IL-10) is an important regulator of immune responses secreted by different cell types. Previous results from our group suggested that the biological effects of this cytokine critically depend on its cellular source. Recent studies reported IL-10 dependent immunosuppressive functions of a specialized subset of regulatory B cells and mast cells. These results relied on adoptive cell transfers, a technique which can potentially introduce artifacts. Therefore, we aimed to readdress these questions in independent models using IL-10 transcriptional reporter mice and various conditional IL-10 mutant mice. Findings in IL-10 reporter system suggested prominent IL-10 transcription in regulatory B cells upon LPS administration. Exposure of mice to contact allergen revealed robust reporter expression in CD8 T cells, moderate to mild reporter expression in CD4 T cells and dendritic cells (DC) respectively, and lack of reporter expression in B cells, mast cells and NK cells in allergen challenged ears. We generated cell-type specific IL-10 mutants by Cre/LoxP-mediated conditional gene inactivation. Efficiency and specificity of Cre-mediated recombination was demonstrated by Southern blot and PCR methods. Various immunogenic challenges in conditional IL-10 mutants did not reveal a role for B cell-derived IL-10 in restraining innate TLR or T cell-dependent inflammatory responses. Likewise, mice with selective inactivation of the il10 gene in mast cells exhibited normal CHS responses and unaltered immune response to CpG oligodeoxynucleotides. On the other hand, DC-specific IL-10 mutants developed excessive inflammatory responses to contact allergens, while innate responses to TLR ligands were not altered. This indicates a non-redundant role for DC-derived IL-10 in contact allergy. Thus, the conditional IL-10 ‘‘knockout’’ mice combined with the novel transcriptional IL-10 reporter system can serve as ideal tools to understand the cell-type specific contributions to IL-10-mediated immune regulation.