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Animal Models |

From the Department of Pathology,*
University of
Washington, Seattle; and the Department of Pediatric
Oncology,
Fred Hutchinson Cancer Research
Center, Seattle, Washington
The tyrosine kinase receptor Ret is expressed in the ureteric
bud and is required for normal renal development. Constitutive loss of
Ret, its co-receptor gfr
-1, or the ligand
glial cell line-derived neurotrophic factor results in renal agenesis.
Transgenic embryos that express a constitutively active form of Ret
(RetMEN2B) under the control of the
dopamine-ß-hydroxylase (DßH) promoter develop profound neuroglial
hyperplasia of their sympathetic ganglia and adrenal medullae. Embryos
from two independent
DßH-RetMEN2B-transgenic
lines exhibit renal malformations. In contrast with
ret-/- embryos, renal maldevelopment in
DßH-RetMEN2B-transgenic
embryos results from primary changes in sympathoadrenal organs
extrinsic to the kidney. The ureteric bud invades the metanephric
mesenchyme normally, but subsequent bud branching and
nephrogenesis are retarded, resulting in severe renal
hypoplasia. Ablation of sympathoadrenal precursors restores normal
renal growth in vivo and in vitro. We
postulate that disruption of renal development results because
RetMEN2B derived from the hyperplastic nervous tissue
competes with endogenous renal Ret for gfr
-1 or other signaling
components. This hypothesis is supported by the observation that renal
malformations, which do not normally occur in a transgenic line
with low levels of
DßH-RetMEN2B
expression, arise in a gdnf+/- background.
However, renal maldevelopment was not recapitulated in kidneys
that were co-cultured with explanted transgenic ganglia in
vitro. Our observations illustrate a novel pathogenic mechanism
for renal dysgenesis that may explain how putative activating mutations
of the RET gene can produce a phenotype usually
associated with RET deficiency.
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