Prenatal Deletion of the RNA-Binding Protein HuD Disrupts Postnatal Cortical Circuit Maturation and Behavior

Abstract

The proper functions of cortical circuits are dependent upon both appropriate neuronal subtype specification and their maturation to receive appropriate signaling. These events establish a balanced circuit that is important for learning, memory, emotion, and complex motor behaviors. Recent research points to mRNA metabolism as a key regulator of this development and maturation process. Hu antigen D (HuD), an RNA-binding protein, has been implicated in the establishment of neuronal identity and neurite outgrowth in vitro. Therefore, we investigated the role of HuD loss of function on neuron specification and dendritogenesis in vivo using a mouse model. We found that loss of HuD early in development results in a defective early dendritic overgrowth phase and pervasive deficits in neuron specification in the lower neocortical layers and defects in dendritogenesis in the CA3 region of the hippocampus. Subsequent behavioral analysis revealed a deficit in performance of a hippocampus-dependent task: the Morris water maze. Further, HuD knock-out (KO) mice exhibited lower levels of anxiety than their wild-type counterparts and were overall less active. Last, we found that HuD KO mice are more susceptible to auditory-induced seizures, often resulting in death. Our findings suggest that HuD is necessary for the establishment of neocortical and hippocampal circuitry and is critical for their function.

Positive feedback between RNA-binding protein HuD and transcription factor SATB1 promotes neurogenesis

“…HuD is expressed by embryonic day 10 during mouse brain development and is one of the earliest markers of neuronal differentiation (37). Although many literature focuses on how HuD regulates neurite extension (38,39) and neuronal maturation (40), only a limited number of studies have addressed HuD function in neural differentiation. Overexpression of HuD leads to neuronal morphology and neuronal marker expression in cultured avian neural crest cells (6) and stalled proliferation of immortalized rat neural progenitor cell line (37); down-regulation of HuD blocks neurite induction in mouse embryonic carcinoma cells (7).…”

Temporally defined neocortical translation and polysome assembly are determined by the RNA-binding protein Hu antigen R

“…Embryonic and postnatal brains were dissected in 1× PBS and postfixed in 4% (wt/vol) paraformaldehyde (pH 7.4) overnight at 4°C. Fixed brains were coronally sectioned on a Leica vibratome at 70 μm and prepared for immunohistochemistry as described (3,43). Primary antibodies and concentrations used are shown in Fig.…”

Regulation of mRNA stability by ARE-binding proteins in synaptic plasticity and memory

“…Defects in neuronal specification in the lower neocortical layers and impaired dendritogenesis in the CA3 region of the hippocampus have also been reported in HuD knockout mice (DeBoer et al, 2014). Importantly, spatial learning is impaired in the knockout mice, demonstrating the critical role of ELAV-like proteins in learning (DeBoer et al, 2014). However, transgenic mice overexpressing HuD concurrently with significant increases in GAP-43 expression also had deficits in hippocampus dependent learning and memory (Bolognani et al, 2007).…”

“…Additionally, these null mutant mice demonstrated abnormal hind limb clasping, which is often associated with cortical deficits, as well as deficits in motor coordination on a rotarod task (Akamatsu et al, 2005). Defects in neuronal specification in the lower neocortical layers and impaired dendritogenesis in the CA3 region of the hippocampus have also been reported in HuD knockout mice (DeBoer et al, 2014). Importantly, spatial learning is impaired in the knockout mice, demonstrating the critical role of ELAV-like proteins in learning (DeBoer et al, 2014).…”

“…These results suggest that the ELAVlike protein HuD is a positive regulator of synaptic plasticity, learning, and memory. The effects of HuD deletion on nervous system development and behavior have been investigated in HuD null mutant mice, with findings that HuD knockout mice have deficits in neurodevelopment and behavior (Akamatsu et al, 2005;DeBoer et al, 2014). Because the targets of HuD, including GAP-43, are involved in cell proliferation and neurite growth, HuD was predicted to be involved in neural differentiation and/or neurite development.…”