Arx together with FoxA2, regulates Shh floor plate expression

Abstract

Mutations in the Aristaless related homeodomain transcription factor (ARX) are associated with a diverse set of X-linked mental retardation and epilepsy syndromes in humans. Although most studies have been focused on its function in the forebrain, ARX is also expressed in other regions of the developing nervous system including the floor plate (FP) of the spinal cord where its function is incompletely understood. To investigate the role of Arx in the FP, we performed gain-of-function studies in the chick using in ovo electroporation, and loss-of-function studies in Arx-deficient mice. We have found that Arx, in conjunction with FoxA2, directly induces Sonic hedgehog (Shh) expression through binding to a Shh floor plate enhancer (SFPE2). We also observed that FoxA2 induces Arx through its transcriptional activation domain whereas Nkx2.2, induced by Shh, abolishes this induction. Our data support a feedback loop model for Arx function; through interactions with FoxA2, Arx positively regulates Shh expression in the FP, and Shh signaling in turn activates Nkx2.2, which suppresses Arx expression. Furthermore, our data are evidence that Arx plays a role as a context dependent transcriptional activator, rather than a primary inducer of Shh expression, potentially explaining how mutations in ARX are associated with diverse, and often subtle, defects.

Aristaless Related Homeobox (ARX) Interacts with β-Catenin, BCL9, and P300 to Regulate Canonical Wnt Signaling

“…One day after IUEP, the dams were sacrificed and the brains were removed. The E13.5 embryonic brains were fixed overnight in 4% paraformaldehyde and prepared for cryosectioning (15 μm) as described [7]. All sections were imaged using Zeiss Zen Pro software driving a Hamamatsu ORCA-Flash 4.0 camera attached to a Zeiss Observer Z1 inverted microscope (Carl Zeiss, Oberkochen, Germany).…”

“…Briefly, primers were designed using Agilent QuikChange Primer Design software and PCR was performed by KOD Xtreme ™ Hot Start DNA Polymerase (Novagen) using pCAG-Arx-IRES-GFP as a template [7]. The PCR products were digested with DpnI (NEB) and transformed into DH10B E .…”

“…Of considerable interest, ARX appears to play independent roles in these two progenitor populations and yet another role in the development of the ventral spinal cord [6–10]. We hypothesized that a distinct repertoire of ARX interaction partners in different cell types confer context-dependent transactivational activities to ARX [7–11]. Thus, identifying the components of the functional complexes in each progenitor population will provide mechanistic understandings as to how one transcription factor can independently regulate distinct cellular functions in different NPCs.…”

Genetics and mechanisms leading to human cortical malformations

“…Arx is expressed in several areas of the nervous system, and in the floorplate Arx together with FoxA2, directly induces Sonic hedgehog (Shh) expression through binding to an Shh floor plate enhancer (SFPE2) [137]. Nkx2.2, induced by Shh, then down-regulates Arx expression, showing hence a regulatory loop during vertebrate development.…”

Epigenomic Landscapes of hESC-Derived Neural Rosettes: Modeling Neural Tube Formation and Diseases

“…Several genetic models showed that this pathway is important for proper neural tube closure and disruption of Shh signaling leads to NTDs (Murdoch and Copp, 2010). In mice, Foxa2 mediates Shh signaling in the floor plate, a critical organizing center for neural tube patterning (Cho et al, 2014; Mansour et al, 2011). Given the poised state of putative FOXA2 enhancers and that the gene is not expressed in NRs (TPM < 1), it may be possible that this gene is activated at a later stage of NT development.…”