The Drosophila ortholog of the Zc3h14 RNA binding protein acts within neurons to pattern axon projection in the developing brain

Abstract

The dNab2 polyadenosine RNA binding protein is the D. melanogaster ortholog of the vertebrate ZC3H14 protein, which is lost in a form of inherited intellectual disability (ID). Human ZC3H14 can rescue D. melanogaster dNab2 mutant phenotypes when expressed in all neurons of the developing nervous system, suggesting that dNab2/ZC3H14 performs well-conserved roles in neurons. However, the cellular and molecular requirements for dNab2/ZC3H14 in the developing nervous system have not been defined in any organism. Here we show that dNab2 is autonomously required within neurons to pattern axon projection from Kenyon neurons into the mushroom bodies, which are required for associative olfactory learning and memory in insects. Mushroom body axons lacking dNab2 project aberrantly across the brain midline and also show evidence of defective branching. Coupled with the prior finding that ZC3H14 is highly expressed in rodent hippocampal neurons, this requirement for dNab2 in mushroom body neurons suggests that dNab2/ZC3H14 has a conserved role in supporting axon projection and branching. Consistent with this idea, loss of dNab2 impairs short-term memory in a courtship conditioning assay. Taken together these results reveal a cell-autonomous requirement for the dNab2 RNA binding protein in mushroom body development and provide a window into potential neurodevelopmental functions of the human ZC3H14 protein.

The poly(A)-binding protein Nab2 functions in RNA polymerase III transcription

“…Interestingly, mutations in ZC3H14 cause a form of autosomal recessive intellectual disability in humans, and Nab2 is needed for normal neuronal function in Drosophila (Pak et al 2011). Thus, Nab2 is important for proper cellular functions, especially in neuronal cells (Kelly et al 2015). Since Nab2 is already known to have important and conserved cellular functions in 3 ′ end processing and mRNA export, it will be of great interest to assess whether its function in RNAPIII transcription is also conserved.…”

The Conserved, Disease-Associated RNA Binding Protein dNab2 Interacts with the Fragile X Protein Ortholog in Drosophila Neurons

“…Patients homozygous for nonsense mutations in ZC3H14 have reduced IQ but lack associated dysmorphic features. Loss of the ubiquitously expressed Drosophila ZC3H14 homolog, dNab2, produces defects in adult viability, motor function, and brain morphology that are fully rescued by neuronal dNab2 re-expression, and partially rescued by human ZC3H14 expression (Kelly et al, 2016; Kelly et al, 2014; Pak et al, 2011). These data reveal an important, and evidently conserved, role for human ZC3H14 and fly dNab2 in neurons.…”

“…Pan-neuron dNab2 depletion within the peripheral nervous system (PNS) and CNS replicates almost all phenotypes resulting from zygotic loss of dNab2, while dNab2 depletion from motor neurons does not (Pak et al, 2011). Moreover, pan-neuron dNab2 depletion impairs short-term memory and disrupts axon projection into the α/β lobes of the mushroom bodies (MBs) (Kelly et al, 2016), twin neuropil structures in the brain required for associative olfactory learning and memory (Heisenberg, 2003). In dNab2 mutants, β-axons misproject across the brain midline and α-axons show a high frequency of branching defects (Kelly et al, 2016).…”

“…Moreover, pan-neuron dNab2 depletion impairs short-term memory and disrupts axon projection into the α/β lobes of the mushroom bodies (MBs) (Kelly et al, 2016), twin neuropil structures in the brain required for associative olfactory learning and memory (Heisenberg, 2003). In dNab2 mutants, β-axons misproject across the brain midline and α-axons show a high frequency of branching defects (Kelly et al, 2016). Selective depletion of dNab2 in Kenyon cells, which give rise to MB α/β axons (Armstrong et al, 1998), is sufficient to phenocopy these dNab2 zygotic defects, and dNab2 re-expression in these cells is sufficient to rescue them (Kelly et al, 2016).…”

“…In dNab2 mutants, β-axons misproject across the brain midline and α-axons show a high frequency of branching defects (Kelly et al, 2016). Selective depletion of dNab2 in Kenyon cells, which give rise to MB α/β axons (Armstrong et al, 1998), is sufficient to phenocopy these dNab2 zygotic defects, and dNab2 re-expression in these cells is sufficient to rescue them (Kelly et al, 2016). However, there is little evidence of how dNab2 regulates bound RNAs and whether this regulation occurs exclusively in the nucleus, as suggested by the nuclear steady-state localization of dNab2, Nab2 and ZC3H14 (Anderson et al, 1993; Leung et al, 2009), or involves a role for dNab2 in cytoplasm.…”