RESUMO
Stochastic activation of clustered Protocadherin (Pcdh) α, ß, and γ genes generates a cell-surface identity code in individual neurons that functions in neural circuit assembly. Here, we show that Pcdhα gene choice involves the activation of an antisense promoter located in the first exon of each Pcdhα alternate gene. Transcription of an antisense long noncoding RNA (lncRNA) from this antisense promoter extends through the sense promoter, leading to DNA demethylation of the CTCF binding sites proximal to each promoter. Demethylation-dependent CTCF binding to both promoters facilitates cohesin-mediated DNA looping with a distal enhancer (HS5-1), locking in the transcriptional state of the chosen Pcdhα gene. Uncoupling DNA demethylation from antisense transcription by Tet3 overexpression in mouse olfactory neurons promotes CTCF binding to all Pcdhα promoters, resulting in proximity-biased DNA looping of the HS5-1 enhancer. Thus, antisense transcription-mediated promoter demethylation functions as a mechanism for distance-independent enhancer/promoter DNA looping to ensure stochastic Pcdhα promoter choice.
Assuntos
Caderinas/genética , Desmetilação do DNA , RNA Antissenso/metabolismo , RNA Longo não Codificante/genética , Animais , Sítios de Ligação , Fator de Ligação a CCCTC/química , Fator de Ligação a CCCTC/metabolismo , Caderinas/metabolismo , Linhagem Celular , Elementos Facilitadores Genéticos , Éxons , Feminino , Humanos , Camundongos , Camundongos Transgênicos , Família Multigênica , Neurônios/citologia , Neurônios/metabolismo , Regiões Promotoras Genéticas , RNA Polimerase II/metabolismo , RNA Antissenso/genética , Transcrição GênicaRESUMO
Expression of Protocadherin (Pcdh) genes is critical to the generation of neuron identity and wiring of the nervous system. Pcdhα genes are arranged in clusters and exhibit a range of expression profiles, from stochastic to deterministic. Because Pcdhα promoters have high sequence identity and share distal enhancers, how distinct neurons choose which gene to express remains unclear. We show that the interplay between multiple enhancers, epigenetics, and genome folding orchestrates differential readouts of the locus across neurons. The probability of Pcdhα promoter choice depends on enhancer/promoter encounters catalyzed by cohesin, whose extrusion trajectories determine the likelihood that an individual promoter can "escape" heterochromatin-mediated silencing. We propose that tunable locus-specific regulatory elements and cell type-specific cohesin activity underlie the generation of cellular diversity by Pcdh genes.
Assuntos
Caderinas , Coesinas , Inativação Gênica , Heterocromatina , Neurônios , Animais , Humanos , Camundongos , Caderinas/genética , Caderinas/metabolismo , Coesinas/metabolismo , Elementos Facilitadores Genéticos , Heterocromatina/metabolismo , Heterocromatina/genética , Camundongos Endogâmicos C57BL , Família Multigênica , Neurônios/metabolismo , Neurônios/fisiologia , Regiões Promotoras Genéticas , Masculino , FemininoRESUMO
Neural type-specific expression of clustered Protocadherin (Pcdh) proteins is essential for the establishment of connectivity patterns during brain development. In mammals, deterministic expression of the same Pcdh isoform promotes minimal overlap of tiled projections of serotonergic neuron axons throughout the brain, while stochastic expression of Pcdh genes allows for convergence of tightly packed, overlapping olfactory sensory neuron axons into targeted structures. How can the same gene locus generate opposite transcriptional programs that orchestrate distinct spatial arrangements of axonal patterns? Here, we reveal that cell type-specific Pcdh expression and axonal behavior depend on the activity of cohesin and its unloader, WAPL (wings apart-like protein homolog). While cohesin erases genomic-distance biases in Pcdh choice, WAPL functions as a rheostat of cohesin processivity that determines Pcdh isoform diversity.