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RB1 gene mutation up-date, a meta-analysis based on 932 reported mutations available in a searchable database

BackgroundRetinoblastoma, a prototype of hereditary cancer, is the most common intraocular tumour in children and potential cause of blindness from therapeutic eye ablation, second tumours in germ line carriers survivors, and even death when left untreated. The molecular scanning of RB1 in search of germ line mutations lead to the publication of more than 900 mutations whose knowledge is important for genetic counselling and the characterization of phenotypic-genotypic relationships.ResultsA searchable database (RBGMdb) has been constructed with 932 published RB1 mutations. The spectrum of these mutations has been analyzed with the following results: 1) the retinoblastoma protein is frequently inactivated by deletions and nonsense mutations while missense mutations are the main inactivating event in most genetic diseases. 2) Near 40% of RB1 gene mutations are recurrent and gather in sixteen hot points, including twelve nonsense, two missense and three splicing mutations. The remainder mutations are scattered along RB1, being most frequent in exons 9, 10, 14, 17, 18, 20, and 23. 3) The analysis of RB1 mutations by country of origin of the patients identifies two groups in which the incidence of nonsense and splicing mutations show differences extremely significant, and suggest the involvement of predisposing ethnic backgrounds. 4) A significant association between late age at diagnosis and splicing mutations in bilateral retinoblastoma patients suggests the occurrence of a delayed-onset genotype. 5) Most of the reported mutations in low-penetrance families fall in three groups: a) Mutations in regulatory sequences at the promoter resulting in low expression of a normal Rb; b) Missense and in-frame deletions affecting non-essential sequence motifs which result in a partial inactivation of Rb functions; c) Splicing mutations leading to the reduction of normal mRNA splicing or to alternative splicing involving either true oncogenic or defective (weak) alleles.ConclusionThe analysis of RB1 gene mutations logged in the RBGMdb has shown relevant phenotype-genotype relationships and provided working hypothesis to ascertain mechanisms linking certain mutations to ethnicity, delayed onset of the disease and low-penetrance. Gene profiling of tumors will help to clarify the genetic background linked to ethnicity and variable expressivity or delayed onset phenotypes.

Cauliflower mosaic virus is preferentially acquired from the phloem by its aphid vectors

Cauliflower mosaic virus (CaMV) is transmitted in a non-circulative manner by aphids following the helper strategy. Helper proteins P2 and P3 act as a bridge between virions and the aphid cuticle. Electronic monitoring of aphid stylet activities (EPG technique), transmission tests and electron microscopy showed that CaMV is preferentially acquired from the phloem by its most common aphid vectors, Brevycorine brassicae and Myzus persicae. We also found that CaMV is semipersistently transmitted and that the rate of acquisition does not follow a typical bimodal curve. Instead, the virus could be acquired from non-phloem tissues at a low and fairly constant rate after one or more intracellular punctures within a few minutes, but the probability of acquisition rose significantly when aphids reached the phase of committed ingestion from the phloem. The acquisition rate of CaMV did not increase with increasing number of intracellular punctures, but the total duration of intracellular puncture was one of the variables selected by the stepwise logistic regression model used to fit the data that best explained acquisition of CaMV. Furthermore, aphids reaching the phloem faster had a higher probability of acquiring the virus. Our results support the hypothesis that multiple intracellular punctures of epidermal and mesophyll cells result in loading aphids with the CaMV-encoded aphid transmission factor (P2), and that aphids, in most cases, subsequently acquire CaMV particles during phloem sap ingestion. Consistently, immunoelectron microscopy showed that P3-virions are frequently found in the sieve element lumen, whereas P2 could not be detected.

Intracellular Salivation Is the Mechanism Involved in the Inoculation of Cauliflower Mosaic Virus by Its Major Vectors Brevicoryne brassicae and Myzus persicae

Abstract Cauliflower mosaic virus (CaMV) is transmitted to crucifers in a noncirculative manner by several aphid species. CaMV is preferentially acquired from the phloem, although acquisition also occurs after brief intracellular stylet punctures of aphid vectors in nonvascular leaf tissues. In the present work, we used the electrical penetration graph technique to study the specific aphid stylet activities and behavioral events leading to the inoculation of CaMV to turnip plants by its two major vectors, Brevicoryne brassicae (L.) and Myzus persicae (Sulzer). Aphids subjected to an 8-h acquisition access time on infected plants were transferred to test plants and removed immediately after specific behavioral events were recorded. CaMV was readily inoculated after the first intracellular puncture in nonvascular tissues by both vector species. Inoculation rate of CaMV by B. brassicae was the highest after a 3-h inoculation access period, regardless of whether aphids had reached the phloem phase during that period. Consistent interspecific differences also were found in the ability of both aphid vectors to retain CaMV. B. brassicae could retain the virus after several intracellular punctures, whereas M. persicae readily lost the virus after performing the same number of intracellular stylet punctures. We concluded that salivation by aphids during successive intracellular stylet punctures in the epidermal and mesophyll cells before reaching the phloem phase are the key behavioral events associated to the inoculation of Cauliflower mosaic virus. The likely location of the viral retention site inside the aphid mouthparts is discussed.

Diagnóstico molecular del retinoblastoma: epidemiología molecular y consejo genético

Fundamento y objetivo: El retinoblastoma, prototipo de cancer hereditario, puede causar ceguera, por enucleacion terapeutica, segundos tumores en pacientes con mutacion germinal e incluso muerte si no se trata. El diagnostico molecular de 213 pacientes a lo largo de 5 anos ha conducido a la deteccion de 106 mutaciones que se analizan desde la perspectiva de la epidemiologia molecular y consejo genetico. Pacientes y metodo: Estudio mutacional (reaccion en cadena de la polimerasa, secuenciacion y analisis de microsatelites) en pacientes con retinoblastoma procedentes de Espana, Cuba, Colombia y Serbia. Resultados: Un 45% de las mutaciones analizadas son nuevas y corresponden a mutaciones de tipo de corrimiento de pauta de lectura, cambio de aminoacido o procesado del acido ribonucleico. Todas las mutaciones sin sentido corresponden a sitios de alta mutabilidad. La tasa de deteccion de mutaciones en pacientes unilaterales esporadicos es alta (22%). En este grupo de pacientes se detecta una mayor incidencia (p = 0,018) de mutaciones de cambio de aminoacido y procesamiento. Espana y Francia muestran una incidencia mayor de mutaciones del procesado (p = 0,0003) que Alemania y el Reino Unido, paises en los que predominan las mutaciones sin sentido (p = 0,0006). Las mutaciones del procesado se asocian al fenotipo de baja penetracion y retraso en la aparicion de tumores (p = 0,018). Conclusiones: La incidencia de mutaciones germinales en pacientes unilaterales y las relaciones fenotipo/genotipo analizadas indican la necesidad del consejo genetico basado en el diagnostico molecular temprano. La mejora de las tecnicas diagnosticas, la caracterizacion funcional de mutaciones asociadas a baja penetrancia o expresividad y el estudio del transcriptoma de los tumores son objetivos necesarios para definir mejor la patogenia del retinoblastoma.