Phenotypic variability in a mouse model for Marfan Syndrome - Identification of phenotype modifier genes

Author(s)

Gustavo Ribeiro Fernandes

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2013-02-06

Examining board members

Lygia da Veiga Pereira Carramaschi; Jose Eduardo Krieger; Regina Celia Mingroni Netto; Paulo Alberto Otto

• Advisor: Lygia da Veiga Pereira Carramaschi

Abstract

The Marfan syndrome (MFS) (OMIM # 154700) is the most common genetic disorder of the connective tissue and is inherited in a autosomal dominant fashion, it has an incidence of 1 in 5,000 individuals. Despite a great clinical variability being one of the \"trademarks\" of the syndrome, the phenotype of the MFS has complete penetrance and its clinical manifestations primarily affect the skeletal, ocular and cardiovascular systems. In order to study the pathogenic mechanisms of MFS was developed a mouse model, named mgΔneoLoxP, which reproduces the skeletal, cardiovascular and pulmonary manifestations of the syndrome. The model was established in inbred mouse strains 129/Sv and C57BL / 6, which phenotypes differ as to age of onset and severity of manifestation. It is possible that allelic differences between these inbred strains alter the phenotyic manifestation of disease, leading to the conclusion that may exist modifier genes involved in the for MFS. This study inteds to use this experimental model to identify phenotype modifier genes of MFS so a better understand the genetic architecture of the syndrome. Altogether, 82 129xB6 F2 heterozygous animals were generated so that a linkage analysis using microsatellite and SNP could be conducted. The linkage analysis using a selective genotyping procedure showed a suggestive linkage of the skeletal phenotype with regions included between positions 56 cM and 68 cM on chromosome 3, and 2 cM and 20 cM on chromosome X; and a significant linkage between positions 41cM and 49 cM on chromosome 6; also showing suggestive linkage of the cardiovascular phenotype from 66 cM to 70 cM on chromosome 4, and 44 cM to 52 cM on chromosome 13. Besides the variability between strains, 129 animals have a wide inner strain phenotypic variability, which in the case of isogenic animals should be caused by random factors or due to epigenetic modifications that may alter the expression level some genes and thus the phenotype. The comparison between animals of the 129 strain with mild and severe alterations led to the identification of 25 differentially expressed genes of which 11 showed relevant functions to the MFS, however it was only possible to measure the expression levels of two genes using real-time PCR, although those did not validate the results obtained from the expression microarray due to a large expression variation in all phenotypic classes. It was also identified 46 pathways that were more frequent in the gene lists obtained from the comparison between the two phenotypic classes of heterozygous animals against 129 wildtype animals. There is a similarity in the function of genes or pathways of interest found in pathways analysis and genes identified, either by differential expression or linkage analisys, and among them there genes already associated with the MFS, such as in the control activity of TGF-B and biogenesis of microfibers in the extracellular matrix, as also genes that were not associated with MFS but are possible phenotype modifier genes, such as genes involved in protein folding and degradation processes and of endocytosis and exocytosis processes of vesicle, which can change the amount of truncated fibrillin-1 available and thus the phenotype (AU)

• FAPESP's process: 09/09747-6 - Clinic variability in a mouse model for the Marfan Syndrome: identification of phenotype modifing genes through usage of microssatelites and microarray
• Grantee: Gustavo Ribeiro Fernandes
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)