RESUMEN
Tlx3 (HOX11L2) is regarded as one of the selector genes in excitatory versus inhibitory fate specification of neurons in distinct regions of the nervous system. Expression of Tlx3 in a post-mitotic immature neuron favors a glutamatergic over GABAergic fate. The factors that regulate Tlx3 have immense importance in the fate specification of glutamatergic neurons. Here, we have shown that Notch target gene, Hes-1, negatively regulates Tlx3 expression, resulting in decreased generation of glutamatergic neurons. Down-regulation of Hes-1 removed the inhibition on Tlx3 promoter, thus promoting glutamatergic differentiation. Promoter-protein interaction studies with truncated/mutated Hes-1 protein suggested that the co-repressor recruitment mediated through WRPW domain of Hes-1 has contributed to the repressive effect. Our results clearly demonstrate a new and unique role for canonical Notch signaling through Hes-1, in neurotransmitter/subtype fate specification of neurons in addition to its known functional role in proliferation/maintenance of neural progenitors.
Asunto(s)
Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Regulación de la Expresión Génica , Proteínas de Homeodominio/metabolismo , Células-Madre Neurales/citología , Secuencia de Aminoácidos , Animales , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/química , Sitios de Unión , Diferenciación Celular , Línea Celular , ADN/metabolismo , Células Madre Embrionarias/citología , Ácido Glutámico/farmacología , Proteínas de Homeodominio/química , Proteínas de Homeodominio/genética , Humanos , Ratones , Datos de Secuencia Molecular , Células-Madre Neurales/metabolismo , Neuronas/metabolismo , Regiones Promotoras Genéticas , Unión Proteica , Estructura Terciaria de Proteína , Transducción de Señal , Factor de Transcripción HES-1 , Ácido gamma-Aminobutírico/farmacologíaRESUMEN
Hes-1 and Hes-5 are downstream effectors of Notch signaling that are known to be involved in different aspects of neural stem cell proliferation and differentiation. Evidence has emerged that Hes-1 expression can be regulated by alternate signaling pathways independent of canonical Notch/CBF1 interaction. This context-dependent differential regulation of Hes-1 expression in neural progenitor gains a lot of importance as it would help in its exponential expansion without the requirement of interaction from neighboring cells during development. Here, we have clearly demonstrated the existence of a population of neural progenitors with Notch/CBF1-independent Hes-1 expression in vitro. Further analysis demonstrated the role of FGF2 in activating Hes-1 expression through the direct binding of ATF2, a JNK downstream target, on Hes-1 promoter. This raises the possibility for the existence of two distinct populations of neural progenitors - one maintained by Hes-1 expression exclusively through Notch-independent mechanism and the other mediating Hes-1 expression through both canonical Notch and FGF2-ATF2 pathway. This alternative pathway will insure a constant expression of Hes-1 even in the absence of canonical Notch intracellular domain-mediated signaling, thereby maintaining a pool of proliferating neural progenitors required during development.