Distinct Molecular and Morphogenetic Properties of Mutations in the Human HNF1β Gene That Lead to Defective Kidney Development

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Abstract
The homeobox transcription factor hepatocyte nuclear factor 1β (HNF1β) is a tissue-specific regulator that plays an essential role in early vertebrate development. In humans, heterozygous mutations in the HNF1β gene are associated with young-onset diabetes as well as a variety of disorders of renal development with cysts as the most consistent feature. This report compares and classifies nine different HNF1β mutations that lead in humans to distinct renal diseases, including solitary functioning kidney, renal dysplasia, glomerulocystic kidney disease, and oligomeganephronia. Analysis of these mutants in vitro identifies mutants that either retain or lack DNA binding. Investigation of the transactivation potential in transfected cell lines reveals a strict correlation between DNA binding and transactivation. Introduction of these mutants into developing Xenopus embryos shows that these mutants interfere with pronephros development, the first kidney form in amphibian. Whereas three mutants lead in Xenopus to a reduction or agenesis of the pronephric tubules and the anterior part of the duct, six mutants generate an enlargement of the pronephric structures. The differential morphogenetic potential in the developing embryo does not strictly correlate with the properties observed in vitro or in transfected cell lines. This suggests that the functional test in the developing embryo defines features of the HNF1β protein that cannot be assessed in cell cultures. The distinct properties observed in the various HNF1β mutants may guide the classification of the phenotypes observed in patients with a mutated HNF1β gene. E-mail: gerhart.ryffel@uni-essen.de

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