title: LMX1B is essential for the maintenance of differentiated podocytes in adult kidneys.
abstract: Mutations of the LMX1B gene cause nail-patella syndrome, a rare autosomal-dominant disorder affecting the development of the limbs, eyes, brain, and kidneys. The characterization of conventional Lmx1b knockout mice has shown that LMX1B regulates the development of podocyte foot processes and slit diaphragms, but studies using podocyte-specific Lmx1b knockout mice have yielded conflicting results regarding the importance of LMX1B for maintaining podocyte structures. In order to address this question, we generated inducible podocyte-specific Lmx1b knockout mice. One week of Lmx1b inactivation in adult mice resulted in proteinuria with only minimal foot process effacement. Notably, expression levels of slit diaphragm and basement membrane proteins remained stable at this time point, and basement membrane charge properties also did not change, suggesting that alternative mechanisms mediate the development of proteinuria in these mice. Cell biological and biophysical experiments with primary podocytes isolated after 1 week of Lmx1b inactivation indicated dysregulation of actin cytoskeleton organization, and time-resolved DNA microarray analysis identified the genes encoding actin cytoskeleton-associated proteins, including Abra and Arl4c, as putative LMX1B targets. Chromatin immunoprecipitation experiments in conditionally immortalized human podocytes and gel shift assays showed that LMX1B recognizes AT-rich binding sites (FLAT elements) in the promoter regions of ABRA and ARL4C, and knockdown experiments in zebrafish support a model in which LMX1B and ABRA act in a common pathway during pronephros development. Our report establishes the importance of LMX1B in fully differentiated podocytes and argues that LMX1B is essential for the maintenance of an appropriately structured actin cytoskeleton in podocytes.
authors.affiliation: Institutes for Molecular and Cellular Anatomy.
authors.forename: Tillmann
authors.initials: T
authors.lastname: Burghardt
authors.forename: Jürgen
authors.initials: J
authors.lastname: Kastner
authors.forename: Hani
authors.initials: H
authors.lastname: Suleiman
authors.forename: Eric
authors.initials: E
authors.lastname: Rivera-Milla
authors.forename: Natalya
authors.initials: N
authors.lastname: Stepanova
authors.forename: Claudio
authors.initials: C
authors.lastname: Lottaz
authors.forename: Marion
authors.initials: M
authors.lastname: Kubitza
authors.forename: Carsten A
authors.initials: CA
authors.lastname: Böger
authors.forename: Sarah
authors.initials: S
authors.lastname: Schmidt
authors.forename: Mathias
authors.initials: M
authors.lastname: Gorski
authors.forename: Uwe
authors.initials: U
authors.lastname: de Vries
authors.forename: Helga
authors.initials: H
authors.lastname: Schmidt
authors.forename: Irmgard
authors.initials: I
authors.lastname: Hertting
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Kopp
authors.forename: Anne
authors.initials: A
authors.lastname: Rascle
authors.forename: Markus
authors.initials: M
authors.lastname: Moser
authors.forename: Iris M
authors.initials: IM
authors.lastname: Heid
authors.forename: Richard
authors.initials: R
authors.lastname: Warth
authors.forename: Rainer
authors.initials: R
authors.lastname: Spang
authors.forename: Joachim
authors.initials: J
authors.lastname: Wegener
authors.forename: Claudia T
authors.initials: CT
authors.lastname: Mierke
authors.forename: Christoph
authors.initials: C
authors.lastname: Englert
authors.forename: Ralph
authors.initials: R
authors.lastname: Witzgall
mesh_terms: D000199:Actins / Q000502:physiology; D000375:Aging; D000818:Animals; D017209:Apoptosis; D002454:Cell Differentiation; D024141:Collagen Type IV / Q000235:genetics; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics; D060850:LIM-Homeodomain Proteins / Q000235:genetics / Q000502:physiology*; D008565:Membrane Proteins / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D009261:Nail-Patella Syndrome / Q000209:etiology; D020411:Oligonucleotide Array Sequence Analysis; D050199:Podocytes / Q000737:chemistry / Q000166:cytology* / Q000648:ultrastructure; D011507:Proteinuria / Q000209:etiology; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D015027:Zebrafish
chemical_list: D000199:Actins; D024141:Collagen Type IV; D047908:Intracellular Signaling Peptides and Proteins; C112149:LIM homeobox transcription factor 1 beta; D060850:LIM-Homeodomain Proteins; D008565:Membrane Proteins; C407223:NPHS2 protein; D014157:Transcription Factors