Spontaneous germline amplification and translocation of a transgene array

Insertional Mutagenesis Confounds the Mechanism of the Morbid Phenotype of a PLNR9C Transgenic Mouse Line

BACKGROUND

A mouse line with heterozygous transgenic expression of phospholamban carrying a substitution of cysteine for arginine 9 (TgPLN^R9C) under the control of α-myosin heavy chain (αMHC) promoter features dilated cardiomyopathy, heart failure, and premature death.

METHODS AND RESULTS

Determination of transgene chromosomal localization by conventional methods shows that in this line the transgenic array of 13 PLN^R9C expression cassettes, arranged in a head-to-tail tandem orientation, have integrated into the bidirectional promoter of the αMHC (Myh6) gene and the gene for the regulatory noncoding RNA Myheart (Mhrt), both of which are known to be involved in cardiac development and pathology. Expression of the noncoding RNA Mhrt in TgPLN^R9C mice exhibits profound deregulation, despite the presence of the second, intact allele.

CONCLUSIONS

The TgPLN^R9C mouse strain is, in the best case, a functionally ambiguous phenocopy of the human PLN^R9C heterozygote, because a similar constellation of genetically programmed events can not occur in a patient. Publications featuring "cardiac-specific overexpression" are focused on the phenotype and typically forgo the definition of the transgene integration site or transgene temporal expression profile, so caution should be exercised in attributing clinical relevance to pathologic phenomena observed in αMHC-driven transgenes.

Comparative genomics and molecular dynamics of DNA repeats in eukaryotes

Repeated elements can be widely abundant in eukaryotic genomes, composing more than 50% of the human genome, for example. It is possible to classify repeated sequences into two large families, "tandem repeats" and "dispersed repeats." Each of these two families can be itself divided into subfamilies. Dispersed repeats contain transposons, tRNA genes, and gene paralogues, whereas tandem repeats contain gene tandems, ribosomal DNA repeat arrays, and satellite DNA, itself subdivided into satellites, minisatellites, and microsatellites. Remarkably, the molecular mechanisms that create and propagate dispersed and tandem repeats are specific to each class and usually do not overlap. In the present review, we have chosen in the first section to describe the nature and distribution of dispersed and tandem repeats in eukaryotic genomes in the light of complete (or nearly complete) available genome sequences. In the second part, we focus on the molecular mechanisms responsible for the fast evolution of two specific classes of tandem repeats: minisatellites and microsatellites. Given that a growing number of human neurological disorders involve the expansion of a particular class of microsatellites, called trinucleotide repeats, a large part of the recent experimental work on microsatellites has focused on these particular repeats, and thus we also review the current knowledge in this area. Finally, we propose a unified definition for mini- and microsatellites that takes into account their biological properties and try to point out new directions that should be explored in a near future on our road to understanding the genetics of repeated sequences.