Mecp2 regulates tnfa during zebrafish embryonic development and acute inflammation.

M Van Der Vaart,T Pietri,D Traver,R Espín-Palazón,B G Weijts,M Bagnat,O Svoboda,A R Muotri,V Sapp

doi:10.1242/dmm.026922

Abstract

ABSTRACTMutations in MECP2 cause Rett syndrome, a severe neurological disorder with autism-like features. Duplication of MECP2 also causes severe neuropathology. Both diseases display immunological abnormalities that suggest a role for MECP2 in controlling immune and inflammatory responses. Here, we used mecp2-null zebrafish to study the potential function of Mecp2 as an immunological regulator. Mecp2 deficiency resulted in an increase in neutrophil infiltration and upregulated expression of the pro- and anti-inflammatory cytokines Il1b and Il10 as a secondary response to disturbances in tissue homeostasis. By contrast, expression of the proinflammatory cytokine tumor necrosis factor alpha (Tnfa) was consistently downregulated in mecp2-null animals during development, representing the earliest developmental phenotype described for MECP2 deficiency to date. Expression of tnfa was unresponsive to inflammatory stimulation, and was partially restored by re-expression of functional mecp2. Thus, Mecp2 is required for tnfa expression during zebrafish development and inflammation. Finally, RNA sequencing of mecp2-null embryos revealed dysregulated processes predictive for Rett syndrome phenotypes.

Highlights

The human X-chromosomal gene methyl-CpG-binding protein 2 (MECP2) was identified as an epigenetic factor capable of binding to methylated DNA (Lewis et al, 1992)
All significantly downregulated genes (Fig. 7B). Notable exceptions to this general tendency for small differences in gene expression levels are bbs4 and nos1 (GO term ‘developmental growth’); sptb, smad9 and casp3b (GO term ‘myeloid cell differentiation’); and DISCUSSION The large body of literature on MECP2 and Rett syndrome (RTT) contains evidence that mutations in MECP2, as well as its overexpression caused by duplication of its genetic locus, result in abnormal functioning of the immune system (Bauer et al, 2015; Cortelazzo et al, 2014; Cronk et al, 2015; Derecki et al, 2012; Leoncini et al, 2015; Pecorelli et al, 2016)
We set out to test the potential function of zebrafish Mecp2 as an epigenetic regulator of immune and inflammatory responses during development

Summary

INTRODUCTION

The human X-chromosomal gene methyl-CpG-binding protein 2 (MECP2) was identified as an epigenetic factor capable of binding to methylated DNA (Lewis et al, 1992). This demonstrates that mecp2-null larvae mount an inflammatory response at 4 dpf and 5 dpf that is detectable at a wholeorganism level, after an early developmental period with no overt signs of systemic inflammation Together, these results show that mecp2-null zebrafish display several RTT features during their development, including growth retardation, GI tract phenotypes and systemic inflammation. We found no difference in gene expression levels of il1b and il between mecp2-null and wild-type larvae during this inflammatory response (Fig. 4E) This demonstrates that the genetic regulation of il1b and il in response to a danger signal is not disturbed by Mecp deficiency, and suggests that their upregulation during mecp2-null larval development is part of an inflammatory response to disturbances in tissue homeostasis. Notable exceptions to this general tendency for small differences in gene expression levels are bbs and nos (GO term ‘developmental growth’); sptb, smad and casp3b (GO term ‘myeloid cell differentiation’); and

DISCUSSION

Findings

MATERIALS AND METHODS