C. Bonifer et al., PREREQUISITES FOR TISSUE-SPECIFIC AND POSITION-INDEPENDENT EXPRESSIONOF A GENE LOCUS IN TRANSGENIC MICE, Journal of molecular medicine, 74(11), 1996, pp. 663-671
Citations number
51
Categorie Soggetti
Medical Laboratory Technology","Genetics & Heredity
The elucidation of general parameters influencing the transcriptional
activation of gene loci at distinct stages of development is an essent
ial prerequisite for a reproducibly successful gene transfer in both g
ene therapy protocols and biotechnology. Up to now research has focuse
d mostly on the identification and characterization of individual cis-
regulatory elements by transient transfection and in vitro assays. How
ever, the most relevant assay system to test gene constructs designed
for gene therapy protocols is the transgenic animal. In such an experi
mental system exogenous genes are usually integrated randomly in the c
hromatin. For gene constructs not fulfilling the requirements for corr
ect gene locus activation this can lead to genomic position effects on
gene expression. The consequences are highly variable expression leve
ls and a disturbance of temporal and spatial expression patterns. Henc
e it is important to examine how cis-elements function in a chromatin
context, and how they cooperate during the developmentally controlled
activation of an entire gene locus. One among a few gene loci which ar
e sufficiently characterized to enable such investigations is the chic
ken lysozyme locus. This review summarizes recent results aimed at ide
ntifying the necessary prerequisites for a reproducibly correct expres
sion of the lysozyme locus in transgenic mice and the implications of
our findings for gene transfer. The complete lysozyme locus is express
ed independent of the chromosomal position and at a high level in macr
ophages of transgenic mice. Correct transgene regulation requires the
cooperation of all cis-regulatory elements. Chromatin of the lysozyme
locus in both the active and the inactive state is highly structured.
Each cis-regulatory element on the chicken lysozyme locus is organized
in its own unique chromatin environment, with nucleosomes specificall
y placed on specific sequences. The transcriptional activation of the
lysozyme locus is accompanied by extensive rearrangements of its chrom
atin structure, which are disturbed when the transgenes are subjects t
o genomic position effects. Based on these results, we propose that a
complete locus is resistant to genomic position effects, and that a di
stinct chromatin architecture of a gene locus is required for its corr
ect activation.