Nephric lineage specification by Pax2 and Pax8.
Journal: 2002/December - Genes and Development
ISSN: 0890-9369
Abstract:
The mammalian kidney develops in three successive steps from the initial pronephros via the mesonephros to the adult metanephros. Although the nephric lineage is specified during pronephros induction, no single regulator, including the transcription factor Pax2 or Pax8, has yet been identified to control this initial phase of kidney development. In this paper, we demonstrate that mouse embryos lacking both Pax2 and Pax8 are unable to form the pronephros or any later nephric structures. In these double-mutant embryos, the intermediate mesoderm does not undergo the mesenchymal-epithelial transitions required for nephric duct formation, fails to initiate the kidney-specific expression of Lim1 and c-Ret, and is lost by apoptosis 1 d after failed pronephric induction. Conversely, retroviral misexpression of Pax2 was sufficient to induce ectopic nephric structures in the intermediate mesoderm and genital ridge of chick embryos. Together, these data identify Pax2 and Pax8 as critical regulators that specify the nephric lineage.
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Genes Dev 16(22): 2958-2970

Nephric lineage specification by Pax2 and Pax8

Research Institute of Molecular Pathology, Vienna Biocenter, A-1030 Vienna, Austria
Corresponding author.
Received 2002 Jun 28; Accepted 2002 Sep 20.

Abstract

The mammalian kidney develops in three successive steps from the initial pronephros via the mesonephros to the adult metanephros. Although the nephric lineage is specified during pronephros induction, no single regulator, including the transcription factor Pax2 or Pax8, has yet been identified to control this initial phase of kidney development. In this paper, we demonstrate that mouse embryos lacking both Pax2 and Pax8 are unable to form the pronephros or any later nephric structures. In these double-mutant embryos, the intermediate mesoderm does not undergo the mesenchymal-epithelial transitions required for nephric duct formation, fails to initiate the kidney-specific expression of Lim1 and c-Ret, and is lost by apoptosis 1 d after failed pronephric induction. Conversely, retroviral misexpression of Pax2 was sufficient to induce ectopic nephric structures in the intermediate mesoderm and genital ridge of chick embryos. Together, these data identify Pax2 and Pax8 as critical regulators that specify the nephric lineage.

Keywords: Pax2, Pax8, genetic redundancy, kidney development, mesenchymal-epithelial transition, lineage specification
Abstract

Kidney development in mammals and birds proceeds in three successive steps that are all characterized by the mesenchymal-to-epithelial transformation of intermediate mesoderm cells. The development of the first kidney, the transient pronephros, is initiated by signals from the somite and surface ectoderm that induce cells in the intermediate mesoderm to undergo the transition to epithelial cells forming the nephric duct (Obara-Ishihara et al. 1999; Mauch et al. 2000). The caudal migration of the nephric duct subsequently induces the adjacent nephrogenic mesoderm to aggregate and form the tubules of the mesonephros, the second embryonic kidney. On further extension, the nephric duct reaches the metanephrogenic mesenchyme at the level of the developing hindlimb, where the ureteric bud evaginates from the nephric duct and invades the surrounding mesenchyme. Both the ureter and mesenchyme subsequently undergo reciprocal inductive interactions to form the nephrons and collecting ducts of the metanephros, the third and adult kidney. Ultimately, the development of the metanephros therefore depends on the proper formation of the nephric duct during pronephros induction (for review, see Saxén 1987; Vainio and Müller 1997).

Targeted mutagenesis in the mouse has identified a multitude of genes that are important for normal kidney development (for review, see Kuure et al. 2000; Davies and Brändli 2002). The majority of these genes are essential for proper morphogenesis of the metanephros with the most severe phenotypes being caused by the inactivation of the transcription factor genes Lim1 (Shawlot and Behringer 1995), WT1 (Kreidberg et al. 1993), and Pax2 (Torres et al. 1995; Favor et al. 1996). Lim1 mutant embryos fail to develop a metanephros and gonads (Shawlot and Behringer 1995), although a nephric duct is initially formed, but then degenerates in the posterior part of the mesonephros (Tsang et al. 2000). The Wilms' tumor suppressor gene WT1 is also necessary for metanephros and gonad development, as the metanephric mesenchyme is unresponsive to inductive signals and undergoes apoptosis in the absence of WT1 function (Kreidberg et al. 1993). The mesonephros, however, still develops in WT1-deficient embryos, although its most caudal tubules fail to form (Sainio et al. 1997). Interestingly, the Pax2 gene is still expressed in the mesonephros of both Lim1 and WT1 mutant embryos (Donovan et al. 1999; Tsang et al. 2000), suggesting that Pax2 acts upstream of these two transcription factors in kidney development. Pax2 is the first known kidney-specific gene to be expressed in the pronephros of the mouse embryo (Bouchard et al. 2000). Despite this early expression, the mesonephric duct is still formed in Pax2-deficient embryos, but then fails to extend to the metanephrogenic mesenchyme because of its rapid degeneration (Torres et al. 1995). As a consequence, the metanephros and genital tracts never develop in Pax2 mutant mice (Torres et al. 1995; Favor et al. 1996). Importantly, however, none of the known gene mutations—including Pax2—interferes with the earliest phase of kidney development, that is, the initial formation of the pro- and mesonephros.

Pax8, another member of the Pax2/5/8 family, is also expressed during pro-, meso-, and metanephros development (Plachov et al. 1990; Pfeffer et al. 1998). Surprisingly, kidney organogenesis is normal in Pax8 mutant mice that die postnatally of a defect in thyroid gland development (Mansouri et al. 1998). By gene replacement in the mouse, we have shown recently that the proteins of the Pax2/5/8 family can substitute for each other in development because of their equivalent biochemical function (Bouchard et al. 2000). By analyzing Pax2,Pax8 double-mutant embryos, we now demonstrate that these two transcription factors have redundant functions in kidney development. Pax2 and Pax8 together are required for the formation of the pro- and mesonephros, as the intermediate mesoderm of Pax2Pax8 embryos was unable to undergo the initial mesenchymal-epithelial transitions and to express the early kidney-specific genes c-ret and Lim1. In complementary experiments, the retroviral misexpression of Pax2 was sufficient to induce ectopic nephric structures in the intermediate mesoderm and genital ridge of chick embryos. Together, these data demonstrate that Pax2 and Pax8 are both necessary and sufficient for specifying the nephric lineage.

Acknowledgments

We thank A. Mansouri and Z. Kozmik for Pax8 DNA clones; C. Theuβl for blastocyst injection; G. Schaffner for DNA sequencing; and C. Hartmann for critical reading of the manuscript. This research was supported by Boehringer Ingelheim and by the Austrian Science Foundation (grant P13601-GEN).

The publication costs of this article were defrayed in part by payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 USC section 1734 solely to indicate this fact.

Acknowledgments

Footnotes

E-MAIL ta.ca.eivinu.pmi.tn@regnilssub; FAX 43-1-798-9370.

Article and publication are at http://www.genesdev.org/cgi/doi/10.1101/gad.240102.

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