Gene conversion in human rearranged immunoglobulin genes

Over the past 20 years, many DNA sequences have been published suggesting that all or part of the V<sub>H</sub> segment of a rearranged immunoglobulin gene may be replaced in vivo. Two different mechanisms appear to be operating. One of these is very similar to primary V(D)J recombination, involving the RAG proteins acting upon recombination signal sequences, and this has recently been proven to occur. Other sequences, many of which show partial V<sub>H</sub> replacements with no addition of untemplated nucleotides at the V<sub>H</sub>–V<sub>H</sub> joint, have been proposed to occur by an unusual RAG-mediated recombination with the formation of hybrid (coding-to-signal) joints. These appear to occur in cells already undergoing somatic hypermutation in which, some authors are convinced, RAG genes are silenced. We recently proposed that the latter type of V<sub>H</sub> replacement might occur by homologous recombination initiated by the activity of AID (activation-induced cytidine deaminase), which is essential for somatic hypermutation and gene conversion. The latter has been observed in other species, but not in human Ig genes, so far. In this paper, we present a new analysis of sequences published as examples of the second type of rearrangement. This not only shows that AID recognition motifs occur in recombination regions but also that some sequences show replacement of central sections by a sequence from another gene, similar to gene conversion in the immunoglobulin genes of other species. These observations support the proposal that this type of rearrangement is likely to be AID-mediated rather than RAG-mediated and is consistent with gene conversion

Características morfofuncionais do trânsito orofaríngeo na bulimia: revisão de literatura Morphofunctional characteristics of the oropharyngeal tract in bulimia: review of literature

TEMA: deglutição e bulimia. OBJETIVO: apresentar e discutir os achados científicos descritos na literatura quanto às características orofaríngeas relacionadas à deglutição em portadores de bulimia nervosa do tipo purgativa. CONCLUSÃO: a bulimia nervosa acarreta uma série de alterações em estruturas e funções que compõem o trânsito orofaríngeo, como erosão dentária, hipersensibilidade, enfraquecimento e fratura dos dentes, problemas de oclusão, cáries, doenças periodontais, dessensibilização intra-oral, hipogeusia, úlceras, granulomas, queilite angular, hipertrofia das glândulas parótidas, tosse e odinofagia. Existe um predomínio na literatura científica de relatos sobre alterações morfológicas em detrimento das funcionais. Poucos relatos abordaram diretamente a relação entre a bulimia e deglutição, apenas mencionando superficialmente as possibilidades de desencadeamento da disfagia orofaríngea.<br>BACKGROUND: deglutition and bulimia. PURPOSE: to submit and discuss the scientific research concerning oropharyngeal characteristics related to deglutition in patients with purging type bulimia nervosa. CONCLUSIONS: bulimia nervosa entails a series of changes in structures and functions that compose the oropharyngeal tract, such as dental erosion, hypersensitivity, weakness and fracture of the teeth, occlusion problems, caries, periodontal diseases, intraoral desensitization, hypogeusia, ulceration, granulomas, angular cheilitis, enlargement of the parotid glands, coughs and odynophagia. There is a prevalence in the scientific literature of reports about morphologic alterations on the detriment of the functional ones. Few reports discussed the relationship between bulimia and deglutition, superficially mentioning the possibilities for triggering oropharyngeal dysphagia