Functional analysis of a zebrafishmyd88mutant identifies key transcriptional components of the innate immune system

Abstract

SUMMARYToll-like receptors (TLRs) are an important class of pattern recognition receptors (PRRs) that recognize microbial and danger signals. Their downstream signaling upon ligand binding is vital for initiation of the innate immune response. In human and mammalian models, myeloid differentiation factor 88 (MYD88) is known for its central role as an adaptor molecule in interleukin 1 receptor (IL-1R) and TLR signaling. The zebrafish is increasingly used as a complementary model system for disease research and drug screening. Here, we describe a zebrafish line with a truncated version of MyD88 as the first zebrafish mutant for a TLR signaling component. We show that this immune-compromised mutant has a lower survival rate under standard rearing conditions and is more susceptible to challenge with the acute bacterial pathogens Edwardsiella tarda and Salmonella typhimurium. Microarray and quantitative PCR analysis revealed that expression of genes for transcription factors central to innate immunity (including NF-ĸB and AP-1) and the pro-inflammatory cytokine Il1b, is dependent on MyD88 signaling during these bacterial infections. Nevertheless, expression of immune genes independent of MyD88 in the myd88 mutant line was sufficient to limit growth of an attenuated S. typhimurium strain. In the case of infection with the chronic bacterial pathogen Mycobacterium marinum, we show that MyD88 signaling has an important protective role during early pathogenesis. During mycobacterial infection, the myd88 mutant shows accelerated formation of granuloma-like aggregates and increased bacterial burden, with associated lower induction of genes central to innate immunity. This zebrafish myd88 mutant will be a valuable tool for further study of the role of IL1R and TLR signaling in the innate immunity processes underlying infectious diseases, inflammatory disorders and cancer.

Animal Models of Tuberculosis: Zebrafish

“…In this period, the embryo solely relies on the innate immune system ( Fig. 1) (van der Sar et al 2004b;Meeker and Trede 2008;Novoa and Figueras 2012;van der Vaart et al 2012), which provides the opportunity to study the contribution of innate immunity to disease in an isolated fashion. Furthermore, it allows for distinguishing between this arm of immunity and a combined innate and adaptive immune response in the context of infection, like in adult fish, which have a complex adaptive immune system akin to that of mammals ( Fig.…”

“…Furthermore, it allows for distinguishing between this arm of immunity and a combined innate and adaptive immune response in the context of infection, like in adult fish, which have a complex adaptive immune system akin to that of mammals ( Fig. 1) (Traver et al 2003;Meeker and Trede 2008;Renshaw and Trede 2012;van der Vaart et al 2012). The finalized whole-genome sequence of zebrafish (Howe et al 2013) reveals that 70% of human genes have at least one obvious zebrafish ortholog.…”

“…Cite this article as Cold Spring Harb Perspect Med 2015;5:a018580 www.perspectivesinmedicine.org quencing studies (Meijer et al 2005;Hegedus et al 2009;Meijer and Spaink 2011;van der Vaart et al 2012). These studies show a modest but complex host response in the early stages of infection (Meijer et al 2005;Hegedus et al 2009).…”

Inflammatory diseases modelling in zebrafish

“…The loss of myd88 [32,33] , an adaptor molecule, central in innate immune signaling [34] , induce predisposition to bacterial infections and compromised expression of immune transcription factors (nfκb, ap-1) and molecules (il-1β, mmp9), proving to be an important molecule in the development of the inflammatory process in zebrafish. NOD proteins are intracellular pattern recognition receptors involved in innate immune response and have been associated with genetic vulnerability to IBD [35] .…”

Deciphering the complexity of macrophage biology and function with the zebrafish model

“…Infection in the hindbrain ventricle of zebrafish larvae with M. marinum was shown to lead to the recruitment and the infection of CCR2 + iNos -macrophages which possess a low microbicidal activity and are thus called "permissive" [30] . One of the mechanisms by which macrophages sense pathogenic microorganisms in mammals and in zebrafish is through the recognition of pathogen molecular patterns (PAMPs) that are present in microbial components with Toll-like receptors (TLRs) [9,31,32] . However, in this context of infection, pathogenic M. marinum sensing is largely independent of myd88, a central regulator of TLRs.…”