RESUMEN
Recent analyses of complete genomes have revealed that alternative splicing became more prevalent and important during eukaryotic evolution. Alternative splicing augments the protein repertoire--particularly that of the human genome--and plays an important role in the development and function of differentiated cell types. However, splicing is also extremely vulnerable, and defects in the proper recognition of splicing signals can give rise to a variety of diseases. In this review, we discuss splicing correction therapies, by using the inherited disease Spinal Muscular Atrophy (SMA) as an example. This lethal early childhood disorder is caused by deletions or other severe mutations of SMN1, a gene coding for the essential survival of motoneurons protein. A second gene copy present in humans and few non-human primates, SMN2, can only partly compensate for the defect because of a single nucleotide change in exon 7 that causes this exon to be skipped in the majority of mRNAs. Thus SMN2 is a prime therapeutic target for SMA. In recent years, several strategies based on small molecule drugs, antisense oligonucleotides or in vivo expressed RNAs have been developed that allow a correction of SMN2 splicing. For some of these, a therapeutic benefit has been demonstrated in mouse models for SMA. This means that clinical trials of such splicing therapies for SMA may become possible in the near future.
Asunto(s)
Atrofia Muscular Espinal/genética , Atrofia Muscular Espinal/terapia , Empalme del ARN , Animales , Exones , Humanos , Ratones , Modelos Animales , Proteína 2 para la Supervivencia de la Neurona Motora/genéticaRESUMEN
In spinal muscular atrophy (SMA), the leading genetic cause of early childhood death, the survival motor neuron 1 gene (SMN1) is deleted or inactivated. The nearly identical SMN2 gene has a silent mutation that impairs the utilization of exon 7 and the production of functional protein. It has been hypothesized that therapies boosting SMN2 exon 7 inclusion might prevent or cure SMA. Exon 7 inclusion can be stimulated in cell culture by oligonucleotides or intracellularly expressed RNAs, but evidence for an in vivo improvement of SMA symptoms is lacking. Here, we unambiguously confirm the above hypothesis by showing that a bifunctional U7 snRNA that stimulates exon 7 inclusion, when introduced by germline transgenesis, can efficiently complement the most severe mouse SMA model. These results are significant for the development of a somatic SMA therapy, but may also provide new means to study pathophysiological aspects of this devastating disease.
Asunto(s)
Terapia Genética , Atrofia Muscular Espinal/genética , Atrofia Muscular Espinal/terapia , ARN Nuclear Pequeño/uso terapéutico , Animales , Secuencia de Bases , Exones , Humanos , Ratones , Ratones Transgénicos , Datos de Secuencia Molecular , Atrofia Muscular Espinal/metabolismo , Empalme del ARN , ARN Nuclear Pequeño/genética , Proteína 2 para la Supervivencia de la Neurona Motora/genética , Proteína 2 para la Supervivencia de la Neurona Motora/metabolismoRESUMEN
The transcription factor regulatory factor X (RFX)-3 regulates the expression of genes required for the growth and function of cilia. We show here that mouse RFX3 is expressed in developing and mature pancreatic endocrine cells during embryogenesis and in adults. RFX3 expression already is evident in early Ngn3-positive progenitors and is maintained in all major pancreatic endocrine cell lineages throughout their development. Primary cilia of hitherto unknown function present on these cells consequently are reduced in number and severely stunted in Rfx3(-/-) mice. This ciliary abnormality is associated with a developmental defect leading to a uniquely altered cellular composition of the islets of Langerhans. Just before birth, Rfx3(-/-) islets contain considerably less insulin-, glucagon-, and ghrelin-producing cells, whereas pancreatic polypeptide-positive cells are markedly increased in number. In adult mice, the defect leads to small and disorganized islets, reduced insulin production, and impaired glucose tolerance. These findings suggest that RFX3 participates in the mechanisms that govern pancreatic endocrine cell differentiation and that the presence of primary cilia on islet cells may play a key role in this process.
Asunto(s)
Proteínas de Unión al ADN/fisiología , Islotes Pancreáticos/fisiología , Factores de Transcripción/fisiología , Animales , Cilios/fisiología , Cilios/ultraestructura , Cruzamientos Genéticos , Proteínas de Unión al ADN/deficiencia , Proteínas de Unión al ADN/genética , Femenino , Ghrelina , Prueba de Tolerancia a la Glucosa , Islotes Pancreáticos/citología , Ratones , Ratones Noqueados , Hormonas Peptídicas/análisis , Embarazo , ARN Mensajero/genética , Factores de Transcripción del Factor Regulador X , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Células Madre/citología , Células Madre/fisiología , Proteína de Unión a TATA-Box/genética , Factores de Transcripción/deficiencia , Factores de Transcripción/genéticaRESUMEN
Glands were the first type of tissues in which the permissive role of gap junctions in the cell-to-cell transfer of membrane-impermeant molecules was shown. During the 40 years that have followed this seminal finding, gap junctions have been documented in all types of multicellular secretory systems, whether of the exocrine, endocrine or pheromonal nature. Also, compelling evidence now indicates that gap junction-mediated coupling, and/or the connexin proteins per se, play significant regulatory roles in various aspects of gland functions, ranging from the biosynthesis, storage and release of a variety of secretory products, to the control of the growth and differentiation of secretory cells, and to the regulation of gland morphogenesis. This review summarizes this evidence in the light of recent reports.