Human Molecular Genetics, Vol 5, 1523-1532, Copyright © 1996 by Oxford University Press
AA Migchielsen, ML Breuer, MS Hershfield and D Valerio
We have shown recently that adenosine deaminase (ADA)-deficient mice die
perinatally with severe liver cell degeneration. In addition to enzyme
substitution, we report the restoration of viability through introduction
of the human ADA gene. The ADA gene is subject to complex developmental and
tissue-specific regulation. To include the cis- regulatory elements
necessary for correct regulation of the human ADA gene, a large transgenic
locus constituting the human ADA gene with 10 kb of 5' and 4 kb of 3'
flanking sequences was generated by co- injection of two overlapping DNA
fragments into murine zygotes. Probably as a result of extrachromosomal
(homologous) recombination between the fragments, one of the two transgenic
lines contained a reconstituted, functional human ADA gene. As in man,
human ADA expression generally was low in these transgenic mice, but high
in the thymus, spleen and gastro-duodenal part of the gut. Apparently, all
cis- regulatory elements essential for a human expression pattern were
incorporated in the transgene and were functional in the murine background.
Similarly to man, the upper alimentary tract of the transgenic mice
revealed low human ADA activity in contrast to extremely high levels of
murine ADA. The human gene probably lacks the cis-regulatory elements that
target high level murine ADA expression to the murine upper alimentary
tract. ADA-deficient mice rescued by introduction of the human ADA
transgene appeared histologically and immunologically normal. Apparently,
human ADA can complement murine ADA in all tissues, even in the epithelium
of the upper alimentary tract where human ADA activity is as much as
70-fold lower than murine ADA activity in wild-type mice. Clearly, the
lethal phenotype of ADA- deficient mice is due to the absence of ADA.
ARTICLES
Full genetic rescue of adenosine deaminase-deficient mice through introduction of the human gene
Department of Medical Biochemistry, University of Leiden, The Netherlands.
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