LEF1/β-Catenin Complex Regulates Transcription of the Cav3.1 Calcium Channel Gene (Cacna1g) in Thalamic Neurons of the Adult Brain

Abstract

␤-Catenin, together with LEF1/TCF transcription factors, activates genes involved in the proliferation and differentiation of neuronal precursor cells. In mature neurons, ␤-catenin participates in dendritogenesis and synaptic function as a component of the cadherin cell adhesion complex. However, the transcriptional activity of ␤-catenin in these cells remains elusive. In the present study, we found that in the adult mouse brain, ␤-catenin and LEF1 accumulate in the nuclei of neurons specifically in the thalamus. The particular electrophysiological properties of thalamic neurons depend on T-type calcium channels. Cav3.1 is the predominant T-type channel subunit in the thalamus, and we hypothesized that the Cacna1g gene encoding Cav3.1 is a target of the LEF1/␤-catenin complex. We demonstrated that the expression of Cacna1g is high in the thalamus and is further increased in thalamic neurons treated in vitro with LiCl or WNT3A, activators of ␤-catenin. Luciferase reporter assays confirmed that the Cacna1G promoter is activated by LEF1 and ␤-catenin, and footprinting analysis revealed four LEF1 binding sites in the proximal region of this promoter. Chromatin immunoprecipitation demonstrated that the Cacna1g proximal promoter is occupied by ␤-catenin in vivo in the thalamus, but not in the hippocampus. Moreover, WNT3A stimulation enhanced T-type current in cultured thalamic neurons. Together, our data indicate that the LEF1/␤-catenin complex regulates transcription of Cacna1g and uncover a novel function for ␤-catenin in mature neurons. We propose that ␤-catenin contributes to neuronal excitability not only by a local action at the synapse but also by activating gene expression in thalamic neurons.

Cognitive flexibility and long-term depression (LTD) are impaired following β-catenin stabilization in vivo

“…β-catenin stabilization was also restricted to adult, differentiated neurons, which are less sensitive to changes in β-catenin levels (37), and much of the available β-catenin was localized to synapses due to its association with cadherin. Finally, nuclear transport of β-catenin may also be more carefully regulated in neurons (38), and levels of Lef1 are relatively low in the hippocampus compared with other brain regions (39), reducing the sensitivity of Wnt signaling to changes in levels of cytoplasmic β-catenin (39).…”

WNT Protein-independent Constitutive Nuclear Localization of β-Catenin Protein and Its Low Degradation Rate in Thalamic Neurons

“…We and others showed that ␤-catenin is abundant in the nuclei of postmitotic thalamic neurons (23,26). The nuclear localization of ␤-catenin in mature neurons is unusual.…”

“…Moreover, nuclear ␤-catenin was able to activate gene expression, because overexpression of AXIN2, which strongly induces ␤-catenin degradation, resulted in about 2-fold reduction of mRNA for Lef1 and Cacna1g (supplemental Fig. S1), which are known ␤-catenin targets (23).…”

“…The other, highly expressed genes in the early and adult dorsal thalamus are Lef1 and Tcf7l2 (19 -23), which encode Wnt-effector transcription factors. Additionally, we recently showed that ␤-catenin accumulates specifically in the nuclei of thalamic neurons and regulates the expression of the gene encoding the Ca v 3.1 voltage-gated calcium channel (23). This channel is involved in T-type currents characteristic of the adult thalamus (24,25).…”

“…The constitutive accumulation of ␤-catenin in the nuclei of postnatal dorsal thalamic neurons (23,26) suggests the persistent activation of the Wnt pathway in this region of the adult brain. However, we report here that neither disruption of the thalamic environment nor inhibition of Wnt/DVL signal transduction affects cytosolic or nuclear levels of ␤-catenin in thalamic neurons, suggesting a mechanism downstream of the WNT receptor.…”