Vertebrate kidney development is a complex process involving the extensive morphogenesis of epithelial tubules. The homeobox gene Lim1 is dynamically expressed during mouse kidney development but its function at each step has been unclear. Kobayashi et al. now show that Lim1 has essential roles throughout tubular morphogenesis (see p. ). Lim1-null mice lack kidneys because nephric duct formation, an early stage of kidney development, fails. To investigate Lim1's function at later stages, the researchers analysed Lim1-null mutants rescued with BAC transgenes, and also tissue-specific Lim1 knockouts and chimaeras. Their findings reveal that Lim1 is involved in ureteric bud formation and nephron patterning. As Lim1, Pax2 and Pax8 are all expressed in the tubule-forming tissues of the three successive kidneys of amniote embryos, the researchers suggest that these transcription factors may form a genetic cassette for tubulogenesis during kidney development.
