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ECKART SCHOTT, MARTIN PAUL AND DETLEV GANTEN
ditional gene to develop models for the in vivo study of its expression and
regulation, as well as possible phenotypic changes induced by the transgene.
Several models have been established that use a construct containing a gene
under its endogenous promoter, leading to overproduction of a gene product in its physiological site of synthesis. However, a limiting factor in the
overproduction of a gene product under its endogenous promoter could be
the down regulation of transcriptional elements, that interact with regulatory elements in the promoter region.
A possibile approach to prevent down-regulation in a transgenic model
is to place the coding region of a gene under the control of a heterologous
promoter. Since extreme overexpression of a genewill prove lethal during
fetallife in many cases, inducible promoters are often useful. While these
promoters show little activity in the non-activated form and, therefore, do
not interfere with normal ontogenesis, expression can easily be induced at
the time, overexpression and its phenotypic consequences are to be studied.
One of the most widely used promoters for this purpose is the metallothionein promoter, which can be induced by heavy metals such as zinc sulfate
supplied in the drinking water. This promoter has been used to overexpress
rat renin and angiotensinogen genes in transgenic mice ( 1) as well as the
human growth hormonein transgenic mice, rabbits and sheep (2). Another
example for a tissue-selective promoter is the transthyretin promoter,
which has been used to overexpress ANP specifically in the liver of transgenic mice (3, 4).
Opposite effects can be obtained by we of antisense constructs, targeted
by a tissue-specific promoter sequence, resulting in tissue-specific downregulation of gene expression in transgenic animals (5). This approach provides opportunity to lower expression rate, since hybridization of the sense
mRNA with the antisense construct will occur. Therefore, production and
release ofthe encoded protein is inhibited. However, in practice, these protocols have proven to be extremely difficult.
Another application for transgenic animals is their use for the study of
gene regulation in vivo by linkage of a reporter gene to the regulatory sequence of a gene under investigation. Reporter genes encode innocuous
gene products that can easily be detected by histochemical staining or other
assays. The most frequently used reporter genes are the ß-galactosidase
(lac-Z) gene derived from E. coli, the firefly luciferase gene and the bacterial
CAT (cloramphenicol-acetyl-transferase) gene. Since these reporter genes
can be used both, in cell culture and in transgenic animals, they open a wide
range of possibilities to investigate the tissue-specific responses to regulatory stimuli on the level of transcription.
ECKART SCHOTT, MARTIN PAUL AND DETLEV GANTEN
ditional gene to develop models for the in vivo study of its expression and
regulation, as well as possible phenotypic changes induced by the transgene.
Several models have been established that use a construct containing a gene
under its endogenous promoter, leading to overproduction of a gene product in its physiological site of synthesis. However, a limiting factor in the
overproduction of a gene product under its endogenous promoter could be
the down regulation of transcriptional elements, that interact with regulatory elements in the promoter region.
A possibile approach to prevent down-regulation in a transgenic model
is to place the coding region of a gene under the control of a heterologous
promoter. Since extreme overexpression of a genewill prove lethal during
fetallife in many cases, inducible promoters are often useful. While these
promoters show little activity in the non-activated form and, therefore, do
not interfere with normal ontogenesis, expression can easily be induced at
the time, overexpression and its phenotypic consequences are to be studied.
One of the most widely used promoters for this purpose is the metallothionein promoter, which can be induced by heavy metals such as zinc sulfate
supplied in the drinking water. This promoter has been used to overexpress
rat renin and angiotensinogen genes in transgenic mice ( 1) as well as the
human growth hormonein transgenic mice, rabbits and sheep (2). Another
example for a tissue-selective promoter is the transthyretin promoter,
which has been used to overexpress ANP specifically in the liver of transgenic mice (3, 4).
Opposite effects can be obtained by we of antisense constructs, targeted
by a tissue-specific promoter sequence, resulting in tissue-specific downregulation of gene expression in transgenic animals (5). This approach provides opportunity to lower expression rate, since hybridization of the sense
mRNA with the antisense construct will occur. Therefore, production and
release ofthe encoded protein is inhibited. However, in practice, these protocols have proven to be extremely difficult.
Another application for transgenic animals is their use for the study of
gene regulation in vivo by linkage of a reporter gene to the regulatory sequence of a gene under investigation. Reporter genes encode innocuous
gene products that can easily be detected by histochemical staining or other
assays. The most frequently used reporter genes are the ß-galactosidase
(lac-Z) gene derived from E. coli, the firefly luciferase gene and the bacterial
CAT (cloramphenicol-acetyl-transferase) gene. Since these reporter genes
can be used both, in cell culture and in transgenic animals, they open a wide
range of possibilities to investigate the tissue-specific responses to regulatory stimuli on the level of transcription.