The Nab2 RNA-binding protein patterns dendritic and axonal projections through a planar cell polarity-sensitive mechanism

Abstract

RNA binding proteins support neurodevelopment by modulating numerous steps in post-transcriptional regulation, including splicing, export, translation, and turnover of mRNAs that can traffic into axons and dendrites. One such RBP is ZC3H14, which is lost in an inherited intellectual disability. The Drosophila melanogaster ZC3H14 ortholog, Nab2, localizes to neuronal nuclei and cytoplasmic ribonucleoprotein granules, and is required for olfactory memory and proper axon projection into brain mushroom bodies. Nab2 can act as a translational repressor in conjunction with the Fragile-X mental retardation protein homolog Fmr1 and shares target RNAs with the Fmr1-interacting RBP Ataxin-2. However, neuronal signaling pathways regulated by Nab2 and their potential roles outside of mushroom body axons remain undefined. Here, we present an analysis of a brain proteomic dataset that indicates that multiple planar cell polarity (PCP) proteins are affected by Nab2 loss, and couple this with genetic data that demonstrate that Nab2 has a previously unappreciated role in restricting the growth and branching of dendrites that elaborate from larval body-wall sensory neurons. Further analysis confirms that Nab2 loss sensitizes sensory dendrites to the genetic dose of PCP components, and that Nab2-PCP genetic interactions are also observed during Nab2-dependent control of axon projection in the central nervous system mushroom bodies. Collectively, these data identify the conserved Nab2 RNA binding protein as a likely component of post-transcriptional mechanisms that limit dendrite growth and branching in Drosophila sensory neurons and genetically link this role to the PCP pathway. Given that mammalian ZC3H14 localizes to dendritic spines and controls spine density in hippocampal neurons, these Nab2-PCP genetic data may highlight a conserved path through which Nab2/ZC3H14 loss affects morphogenesis of both axons and dendrites in diverse species.

The RNA binding protein Nab2 regulates splicing of the RhoGEFtriotranscript to govern axon and dendrite morphology

“…The ZC3H14 protein is evolutionarily conserved among eukaryotes and has been studied in Mus musculus ( Zc3h14 ) (Guthrie et al ., 2011; Pak et al ., 2011; Soucek et al ., 2016), Caenorhabditis elegans ( sut-2 ) (Guthrie et al ., 2009), Sacchromyces cerevisiae (Nab2) (Anderson et al ., 1993; Green et al ., 2002; Hector et al ., 2002; Marfatia et al ., 2003; Kelly et al ., 2007; Kelly et al ., 2010; Schmid et al ., 2015; Soucek et al ., 2016), Sacchromyces pombe (Nab2) (Grenier St-Sauveur et al ., 2013), and Drosophila melanogaster (Nab2) (Pak et al ., 2011; Kelly et al ., 2016; Fasken et al ., 2019; Lee et al ., 2020; Corgiat et al ., 2021; Corgiat et al ., 2022; Rounds et al ., 2022; Jalloh and Lancaster et al ., 2023). These studies have collectively uncovered molecular and neuronal functions for this conserved ZnF Pab.…”

“…Biochemical studies show that Nab2 interacts with Fmr1, the fly homolog of Fragile X Syndrome RBP, FMRP (Wan et al ., 2000), and that these two RBPs co-regulate mushroom body morphology and olfactory memory through a mechanism likely to involve translational repression of shared Nab2-Fmr1 target RNAs (Bienkowski et al ., 2017). Beyond the brain, Nab2 limits dendritic branching of class IV dorsal dendritic arborization (ddaC) sensory neurons through a mechanism involving the planar cell polarity (PCP) pathway (Corgiat et al ., 2022), suggesting that Nab2 controls RNA targets encoding regulators of the actin cytoskeleton. Our recent work studying the effect of Nab2 loss on the brain transcriptome revealed that Nab2 is required for proper splicing of ~150 mRNAs (Jalloh and Lancaster et al ., 2023).…”

The making of the Drosophila mushroom body

“…Nab2 is expressed in adult and pupal KCs (no data is available for Frontiers in Physiology frontiersin.org larval KCs). The MBs in Nab2 −/− flies display high penetrance of α lobe-missing and β lobe overextension phenotypes that can be rescued by specific expression of wild-type Nab2 in the KCs (Kelly et al, 2016;Corgiat et al, 2022). Removing one copy of Vang, Appl, or dsh significantly rescues the Nab2 homozygous mutant MB phenotypes, supporting that Nab2 regulates KC axonal development by tuning down PCP signaling (Corgiat et al, 2022).…”

“…RNA-binding protein Nab2 has been found to regulate the levels of PCP components. Comparing the proteomes of wild-type and Nab2 homozygous mutant flies revealed that PCP pathway proteins, including Vang, APPL, and several putative PCP effectors, are differentially expressed in Nab2 mutant flies (Corgiat et al, 2022). Nab2 is expressed in adult and pupal KCs (no data is available for Frontiers in Physiology frontiersin.org larval KCs).…”

“…The MBs in Nab2 −/− flies display high penetrance of α lobe-missing and β lobe overextension phenotypes that can be rescued by specific expression of wild-type Nab2 in the KCs (Kelly et al, 2016;Corgiat et al, 2022). Removing one copy of Vang, Appl, or dsh significantly rescues the Nab2 homozygous mutant MB phenotypes, supporting that Nab2 regulates KC axonal development by tuning down PCP signaling (Corgiat et al, 2022). Genetic interaction experiments have also revealed that Nab2 works cooperatively with Fragile X messenger ribonucleoprotein 1 (FMRP) and antagonistically with Ataxin-2 (Atx2) to regulate α branch growth (Bienkowski et al, 2017;Rounds et al, 2022).…”