The H3K4me3/2 histone demethylase RBR-2 controls axon guidance by repressing the actin-remodeling gene wsp-1

Abstract

The dynamic regulation of histone modifications is important for modulating transcriptional programs during development. Aberrant H3K4 methylation is associated with neurological disorders, but how the levels and the recognition of this modification affect specific neuronal processes is unclear. Here, we show that RBR-2, the sole homolog of the KDM5 family of H3K4me3/2 demethylases in Caenorhabditis elegans, ensures correct axon guidance by controlling the expression of the actin regulator wsp-1. Loss of rbr-2 results in increased levels of H3K4me3 at the transcriptional start site of wsp-1, with concomitant higher wsp-1 expression responsible for defective axon guidance. In agreement, overexpression of WSP-1 mimics rbr-2 loss, and its depletion restores normal axon guidance in rbr-2 mutants. NURF-1, an H3K4me3-binding protein and member of the chromatin-remodeling complex NURF, is required for promoting aberrant wsp-1 transcription in rbr-2 mutants and its ablation restores wild-type expression of wsp-1 and axon guidance. Thus, our results establish a precise role for epigenetic regulation in neuronal development by demonstrating a functional link between RBR-2 activity, H3K4me3 levels, the NURF complex and the expression of WSP-1.

JMJD-1.2/PHF8 controls axon guidance by regulating Hedgehog-like signaling

“…The fact that rbr-2 and jmjd-1.2 share similar phenotypes when ablated, are both required during embryogenesis and bind H3K4me3 through their PHD domains, suggests that these histone demethylases might regulate axon guidance in a concerted manner. Indeed, we previously reported that rbr-2;jmjd-1.2 double mutants show similar levels of PVQ defects as the single mutants (Mariani et al, 2016), confirming that rbr-2 and jmjd-1.2 act in a common pathway regulating axon guidance. Altogether, these findings confirm that epigenetic factors are essential for the correct execution of developmental processes, providing novel insights into how neuronal development is achieved.…”

“…It is possible that altered actin dynamics counteract the effects of increased Hh signaling by regulating Hh trafficking and secretion. However, based on our previous findings that misexpression of actin regulators in PVQ neurons causes aberrant axon guidance (Mariani et al, 2016) and on our overexpression experiments in the wsp-1 mutant background, we favor a hypothesis (Fig. 5) in which JMJD-1.2 modulates the expression of Hh-related proteins in neuronal and hypodermal cells, which, after secretion, activate a signaling pathway controlling actin remodeling and axon guidance in target neurons.…”

“…rbr-2 is the sole nematode homolog of the human XLMR gene JARID1C (KDM5C), and controls axon guidance in a similar subset of neurons by reducing the expression of actin-related genes, including wsp-1 (Mariani et al, 2016). The fact that rbr-2 and jmjd-1.2 share similar phenotypes when ablated, are both required during embryogenesis and bind H3K4me3 through their PHD domains, suggests that these histone demethylases might regulate axon guidance in a concerted manner.…”

“…RNA isolation, cDNA synthesis and qPCR were performed as described previously (Mariani et al, 2016). The measures were normalized to Y45F10D.4 (Zhang et al, 2012).…”

“…The nematode Caenorhabditis elegans presents an excellent model to investigate these processes on a simpler and more tractable scale: its nervous system consists of 302 cells, whose morphology, function and connectivity have been extensively characterized (Sulston, 1983;White et al, 1986). Many chromatin regulators are conserved in C. elegans and important information regarding the role of these proteins in neuronal development has recently been obtained using this model system (Weinberg et al, 2013;Zheng et al, 2013;Mariani et al, 2016). PHF8 shares high homology with the C. elegans JMJD-1.2 protein, which retains both the JmjC and the PHD finger domains.…”