Transcription factor Sp4 regulates expression of nervous wreck 2 to control NMDAR1 levels and dendrite patterning.

Glutamatergic signaling through N-methyl-d-aspartate receptors (NMDARs) is important for neuronal development and plasticity and is often dysregulated in psychiatric disorders. Mice mutant for the transcription factor Sp4 have reduced levels of NMDAR subunit 1 (NR1) protein, but not mRNA, and exhibit behavioral and memory deficits (Zhou et al., [2010] Human Molecular Genetics 19: 3797-3805). In developing cerebellar granule neurons (CGNs), Sp4 controls dendrite patterning (Ramos et al., [2007] Proc Natl Acad Sci USA 104: 9882-9887). Sp4 target genes that regulate dendrite pruning or NR1 levels are not known. Here we report that Sp4 activates transcription of Nervous Wreck 2 (Nwk2; also known as Fchsd1) and, further, that Nwk2, an F-BAR domain-containing protein, mediates Sp4-dependent regulation of dendrite patterning and cell surface expression of NR1. Knockdown of Nwk2 in CGNs increased primary dendrite number, phenocopying Sp4 knockdown, and exogenous expression of Nwk2 in Sp4-depleted neurons rescued dendrite number. We observed that acute Sp4 depletion reduced levels of surface, but not total, NR1, and this was rescued by Nwk2 expression. Furthermore, expression of Nr1 suppressed the increase in dendrite number in Sp4- or Nwk2- depleted neurons. We previously reported that Sp4 protein levels were reduced in cerebellum of subjects with bipolar disorder (BD) (Pinacho et al., [2011] Bipolar Disorders 13: 474-485). Here we report that Nwk2 mRNA and NR1 protein levels were also reduced in postmortem cerebellum of BD subjects. Our data suggest a role for Sp4-regulated Nwk2 in NMDAR trafficking and identify a Sp4-Nwk2-NMDAR1 pathway that regulates neuronal morphogenesis during development and may be disrupted in bipolar disorder.

Transcription factor SP4 is a susceptibility gene for bipolar disorder.

The Sp4 transcription factor plays a critical role for both development and function of mouse hippocampus. Reduced expression of the mouse Sp4 gene results in a variety of behavioral abnormalities relevant to human psychiatric disorders. The human SP4 gene is therefore examined for its association with both bipolar disorder and schizophrenia in European Caucasian and Chinese populations respectively. Out of ten SNPs selected from human SP4 genomic locus, four displayed significant association with bipolar disorder in European Caucasian families (rs12668354, p = 0.022; rs12673091, p = 0.0005; rs3735440, p = 0.019; rs11974306, p = 0.018). To replicate the genetic association, the same set of SNPs was examined in a Chinese bipolar case control sample. Four SNPs displayed significant association (rs40245, p = 0.009; rs12673091, p = 0.002; rs1018954, p = 0.001; rs3735440, p = 0.029), and two of them (rs12673091, rs3735440) were shared with positive SNPs from European Caucasian families. Considering the genetic overlap between bipolar disorder and schizophrenia, we extended our studies in Chinese trios families for schizophrenia. The SNP7 (rs12673091, p = 0.012) also displayed a significant association. The SNP7 (rs12673091) was therefore significantly associated in all three samples, and shared the same susceptibility allele (A) across all three samples. On the other hand, we found a gene dosage effect for mouse Sp4 gene in the modulation of sensorimotor gating, a putative endophenotype for both schizophrenia and bipolar disorder. The deficient sensorimotor gating in Sp4 hypomorphic mice was partially reversed by the administration of dopamine D2 antagonist or mood stabilizers. Both human genetic and mouse pharmacogenetic studies support Sp4 gene as a susceptibility gene for bipolar disorder or schizophrenia. The studies on the role of Sp4 gene in hippocampal development may provide novel insights for the contribution of hippocampal abnormalities in these psychiatric disorders.

Distinct roles of HF-1b/Sp4 in ventricular and neural crest cells lineages affect cardiac conduction system development.

The heterogeneous cell types of the cardiac conduction system are responsible for coordinating and maintaining rhythmic contractions of the heart. While it has been shown that the cells of the conduction system are derived from myocytes, additional cell types, including neural crest cells, may play a role in the development and maturation of these specialized cell lineages. Previous work has shown that the expression of the hf-1b gene is required for specification of the cardiac conduction system. Using Cre-Lox technology, we conditionally mutated the hf-1b gene in the ventricular and the neural crest cell lineages. Cx40 immunohistochemistry on HF-1b tissue-restricted knockouts revealed a requirement for HF-1b in the cardiomyogenic lineage. Electrophysiological studies identified a second requirement for HF-1b in the neural crest-derived cells. Absence of HF-1b in the neural crest led to atrial and atrioventricular dysfunction resulting from deficiencies in the neurotrophin receptor trkC. Therefore, in this study, we document that a single transcription factor, HF-1b, acts through two separate cell types to direct distinct functions of the cardiac conduction system.