High-Throughput Analysis of Promoter Occupancy Reveals New Targets for Arx, a Gene Mutated in Mental Retardation and Interneuronopathies

Lim

et al. 2014

Developmental Biology

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.

Section: Resultsmentioning

confidence: 99%

Arx together with FoxA2, regulates Shh floor plate expression

Lim

et al. 2014

Developmental Biology

“…Although much has been learned about the role of Arx in inter-neuron migration and maturation at critical ages, the large number of transcriptional targets and endophenotype complexity are reminders that our understanding of the epileptogenic role of this pleiotropic transcription factor is only beginning (62, 63). The findings described here identify early disease-modifying effects of gene expression remodeling by transient stimulation with an endogenous steroid hormone and a promising avenue for exploring new treatment options for a devastating infantile epilepsy syndrome.…”

Section: Discussionmentioning

confidence: 99%

Neonatal Estradiol Stimulation Prevents Epilepsy in Arx Model of X-Linked Infantile Spasms Syndrome

2014

Infantile spasms are a catastrophic form of pediatric epilepsy with inadequate treatment. In patients, mutation of ARX, a transcription factor selectively expressed in neuronal precursors and adult inhibitory interneurons, impairs cell migration and causes a major inherited subtype of the disease X-linked infantile spasms syndrome. Using an animal model, the Arx(GCG)10+7 mouse, we determined that brief estradiol (E2) administration during early postnatal development prevented spasms in infancy and seizures in adult mutants. E2 was ineffective when delivered after puberty or 30 days after birth. Early E2 treatment altered mRNA levels of three downstream targets of Arx (Shox2, Ebf3, and Lgi1) and restored depleted interneuron populations without increasing GABAergic synaptic density. Postnatal E2 treatment may induce lasting transcriptional changes that lead to enduring disease modification and could potentially serve as a therapy for inherited interneuronopathies.

“…The perturbed local dorsoventral pattern may affect the area that will give rise, among others, to group 1 DA neurons. On the other hand, it has been recently shown by chromatin immunoprecipitation experiments that ARX directly binds to the TH promoter in transfected neuroblastoma cells (Quillé et al, 2011), suggesting that Arx may be involved in direct regulation of TH expression. The prethalamic DA phenotype we observe in the zebrafish larva may be caused by Arx action at different levels during prethalamic development.…”

Section: Discussionmentioning

confidence: 99%

Analysis of transcriptional codes for zebrafish dopaminergic neurons reveals essential functions of Arx and Isl1 in prethalamic dopaminergic neuron development

Filippi

Jainok

Driever

2012

Developmental Biology

Distinct groups of dopaminergic neurons develop at defined anatomical sites in the brain to modulate function of a large diversity of local and far-ranging circuits. However, the molecular identity as judged from transcription factor expression has not been determined for all dopaminergic groups. Here, we analyze regional expression of transcription factors in the larval zebrafish brain to determine co-expression with the Tyrosine hydroxylase marker in dopaminergic neurons. We define sets of transcription factors that clearly identify each dopaminergic group. These data confirm postulated relations to dopaminergic groups defined for mammalian systems. We focus our functional analysis on prethalamic dopaminergic neurons, which co-express the transcription factors Arx and Isl1. Morpholino-based knockdown reveals that both Arx and Isl1 are strictly required for prethalamic dopaminergic neuron development and appear to act in parallel. We further show that Arx contributes to patterning in the prethalamic region, while Isl1 is required for differentiation of prethalamic dopaminergic neurons.