RESUMEN
The basic helix-loop-helix factor Math5 (Atoh7) is critical for the determination of retinal ganglion cell (RGC) fate in mice. Recently, genome-wide association studies have identified the ATOH7 locus as a major determinant of variation in the human optic disc area, which is directly correlated with the RGC number. These studies suggest that the level of Math5 expression may determine the ultimate number of RGCs. To test this hypothesis, we systematically compared optic nerve area and RGC axon number in C57BL/6J congenic Math5+/- and +/+ mice at young adult and neonatal ages by transmission electron microscopy. Optic disc area and RGC abundance were not significantly different in adults, but heterozygotes had thinner optic nerves and 25-30% fewer RGCs at birth than wild-type littermates (P<0.05). Our results suggest that Math5 dosage is important for the genesis, but not the ultimate number, of RGCs. Our findings highlight the importance of ganglion cell culling as a compensatory mechanism for retinal homeostasis, and support a quantitative role for Math5 in RGC specification.
Asunto(s)
Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/biosíntesis , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/genética , Dosificación de Gen/fisiología , Proteínas del Tejido Nervioso/biosíntesis , Proteínas del Tejido Nervioso/genética , Neurogénesis/fisiología , Células Ganglionares de la Retina/fisiología , Animales , Ratones , Ratones de la Cepa 129 , Ratones Congénicos , Ratones Endogámicos C57BLRESUMEN
Individuals with nonsyndromic congenital retinal nonattachment (NCRNA) are totally blind from birth. The disease afflicts â¼1% of Kurdish people living in a group of neighboring villages in North Khorasan, Iran. We found that NCRNA is caused by a 6,523-bp deletion that spans a remote cis regulatory element 20 kb upstream from ATOH7 (Math5), a bHLH transcription factor gene that is required for retinal ganglion cell (RGC) and optic nerve development. In humans, the absence of RGCs stimulates massive neovascular growth of fetal blood vessels in the vitreous and early retinal detachment. The remote ATOH7 element appears to act as a secondary or 'shadow' transcriptional enhancer. It has minimal sequence similarity to the primary enhancer, which is close to the ATOH7 promoter, but drives transgene expression with an identical spatiotemporal pattern in the mouse retina. The human transgene also functions appropriately in zebrafish, reflecting deep evolutionary conservation. These dual enhancers may reinforce ATOH7 expression during early critical stages of eye development when retinal neurogenesis is initiated.
Asunto(s)
Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/genética , Elementos de Facilitación Genéticos/genética , Neurogénesis/genética , Retina/citología , Desprendimiento de Retina/genética , Eliminación de Secuencia/genética , Adolescente , Animales , Animales Modificados Genéticamente , Preescolar , Mapeo Cromosómico , Cromosomas Humanos Par 10 , Biología Computacional/métodos , Consanguinidad , Análisis Mutacional de ADN , Embrión de Mamíferos , Salud de la Familia , Femenino , Citometría de Flujo , Regulación del Desarrollo de la Expresión Génica/genética , Humanos , Irán/etnología , Proteínas Luminiscentes/genética , Imagen por Resonancia Magnética , Masculino , Ratones , Persona de Mediana Edad , Polimorfismo de Nucleótido Simple/genética , Retina/embriología , Desprendimiento de Retina/congénito , Desprendimiento de Retina/patología , Colículos Superiores/patología , Pez Cebra/crecimiento & desarrolloRESUMEN
The basic helix-loop-helix (bHLH) transcription factor Math5 (Atoh7) is required for retinal ganglion cell (RGC) and optic nerve development. Using Math5-lacZ knockout mice, we have identified an additional expression domain for Math5 outside the eye, in functionally connected structures of the central auditory system. In the adult hindbrain, the cytoplasmic Math5-lacZ reporter is expressed within the ventral cochlear nucleus (VCN), in a subpopulation of neurons that project to medial nucleus of the trapezoid body (MNTB), lateral superior olive (LSO), and lateral lemniscus (LL). These cells were identified as globular and small spherical bushy cells based on their morphology, abundance, distribution within the cochlear nucleus (CN), co-expression of Kv1.1, Kv3.1b and Kcnq4 potassium channels, and projection patterns within the auditory brainstem. Math5-lacZ is also expressed by cochlear root neurons in the auditory nerve. During embryonic development, Math5-lacZ was detected in precursor cells emerging from the caudal rhombic lip from embryonic day (E)12 onwards, consistent with the time course of CN neurogenesis. These cells co-express MafB and are post-mitotic. Math5 expression in the CN was verified by mRNA in situ hybridization, and the identity of positive neurons was confirmed morphologically using a Math5-Cre BAC transgene with an alkaline phosphatase reporter. The hindbrains of Math5 mutants appear grossly normal, with the exception of the CN. Although overall CN dimensions are unchanged, the lacZ-positive cells are significantly smaller in Math5 -/- mice compared to Math5 +/- mice, suggesting these neurons may function abnormally. The auditory brainstem response (ABR) of Math5 mutants was evaluated in a BALB/cJ congenic background. ABR thresholds of Math5 -/- mice were similar to those of wild-type and heterozygous mice, but the interpeak latencies for Peaks II-IV were significantly altered. These temporal changes are consistent with a higher-level auditory processing disorder involving the CN, potentially affecting the integration of binaural sensory information.
