Expression Systems to Analyze Transgenes in the Heart

Recent insights from molecular and cellular biology have contributed to a better understanding of potential causes of cardiac hypertrophy and heart failure. Especially, the use of transgenic mice has become increasingly useful in determining the molecular mechanisms of cardiac hypertrophy and heart failure. As shown in Table 15-1, there is a diverse and rapidly growing list of genes that can trigger features of hypertrophy and associated cardiomyopathy after their cardiac-specific (over)expression. The transgenic mouse models listed in this table 15-1 have been produced by pronuclear injection into fertilised oocytes. This technique results in a variable number of transgene copies that integrate into random genomic loci. The variable copy number and the random integration may independently affect the level of expression of the transgene, the pattern and the tissue specificity1-3. For example, dense chromatin at the site of integration may result in (partial) silencing of the DNA construct, the presence of regulatory sequences (e.g., enhancers) at the site of integration can result in ectopic expression patterns and the variable number of integrated copies can result in variation in expression level. The severity of these problems increases strongly when decreasing the size of the regulatory DNA fragment that is used to drive the transgene.